Category Archives: practice

non-prompted, a sandbox of sorts. use it for whatever you’d like

Black Holes 5: Inklings & Obsessions

by Shane L. Larson

There are many exotic phenomena in astrophysics — some pervade the public consciousness, and others do not. Most folks have heard of the “Big Bang” and probably about “dark matter.” Fewer people have heard of the “Cosmic Microwave Background” or “neutron stars.” Perhaps even fewer have heard of “cosmic strings” or “radio jets.” But of all the strange and wonderful things astronomers and physicists have contemplated, the most universally known and recognized are probably “black holes.” Just about everyone has heard of black holes, and just about everyone has some cool science factoid they know about black holes and keep in their pocket — they pull the factoid out anytime the subject of black holes come up because the factoids typically MELT YOUR BRAIN.

On the left, an optical image from the Digitized Sky Survey shows Cygnus X-1, outlined in a red box. Cygnus X-1 is located near large active regions of star formation in the Milky Way, as seen in this image that spans some 700 light years across. An artist’s illustration on the right depicts what astronomers think is happening within the Cygnus X-1 system. Cygnus X-1 is a so-called stellar-mass black hole, a class of black holes that comes from the collapse of a massive star. New studies with data from Chandra and several other telescopes have determined the black hole’s spin, mass, and distance with unprecedented accuracy.

I find black hole factoids to be a curious mix of some things that are true, some things that are speculative but possibly true, and some things are are outright fiction. Where do all of the exotic facts about black holes come from, how do we all learn them, and why are some right and some wrong? Wondering about this led me to contemplate when I first heard about black holes.

Black holes have long been a passion of mine — my mom will tell you I was always kind of obsessed with them. But when did I first hear about and learn about them? I certainly can’t answer that question definitively, but I do know some things about my early exposure, so I can try to understand what strange and awesome ideas first attracted my attention.

The earliest encounter of which I am certain is during the 1979/1980 timeframe. This was the time that many people saw Disney’s epic space opera The Black Hole, replete with adorable robots, killer robots, really awful bad dialog, and archetypical mad scientists. It has often been derided for its scientific inaccuracies (most notably by Neil deGrasse Tyson [link]). I definitely saw The Black Hole. Multiple times. And I still watch it sometimes. Neil’s right, there is a lot of inaccurate science about black holes in The Black Hole, but there is a lot that I think was okay too (more on that later). There are definitely modern movies that get the science more uniformly correct (Interstellar), but I don’t mind The Black Hole — certainly not as much as Neil. The point here is this is a known anchor point in my love affair with black holes.

So what could a movie like The Black Hole teach me about real black holes? If you ask almost anyone, they know the correct fundamental thing: a black hole is an object whose gravity is so strong, not even light can escape — even The Black Hole got that right. Since nothing can travel faster than light, nothing can escape. If you fall into a black hole, your fate is sealed. It is this idea of being trapped forever, without recourse or hope of rescue, that lies at the heart of our fascination with black holes. They are strange; indubitably. But to be inescapable suggests a kind of absolute and infinite supremacy. 

Me in elementary school. I’m not sure what I’m doing, but I’m pretty sure I’m not getting into trouble! [Image: Pat Larson]

In 1979/1980 I was in fifth grade, and I was gobbling this stuff up left and right. I was a well known fixture in both my school library (Hygiene Elementary School, in Colorado), and in the Longmont Public Library, where my mom had gotten special dispensation for me to have an “adult” library card so I could prowl through all the science books in the grown-up section. My parents also exposed me to a steady diet of books at home, and while they were all nominally “family books,” some of them made it to the bookcase by my bed and never went through anyone else’s hands. In 1980 one such book was Roy Gallant’s lavishly illustrated Our Universe, published by the National Geographic Society.  I was certainly enraptured with outer space by then, steadily fed by the ongoing exploits of Viking and Voyager as they played out on the pages of National Geographic. But this book — this book. Blew. My. Mind.

It is a book filled with great pictures from an exquisite generation of space probes, and from the best telescopes the world knew in the pre-Hubble era. But the art and scientific illustrations are what sucked me in. Paintings of the surface of Venus. Speculations of what weird alien lifeforms evolution could have created. Stupendous cutaways of planetary interiors and atmospheres. All of it was linked together with Gallant’s trademark lucid storytelling.  This ode to the Universe captured my mind and imagination and never let go. That first copy my parents gave me was read cover-to-cover, and carried for miles and years everywhere I went, pulled out of my backpack in moments of wonder and curious indulgence.

Examples of the art and technical imagery in Roy Gallant’s “Our Universe.”

Near the end of the book, Gallant talks about black holes in just 4 short paragraphs, but accompanies the text with a lavish, full-page artist’s idealization of a black hole in space, tugging on a nearby star, bending the shape of spacetime, and absorbing a beam of light that was inexorably caught in its pull.

He asks in the caption of the picture, “Can you imagine a star so massive that its gravitation eventually crushes it out of existence, leaving only a black hole in the sky?” This is classic Gallant, imploring the reader to immerse themselves in the mystery, throw caution to the wind, and employ their imagination — take what little knowledge you have and simply speculate. That is where good ideas come from, and it is the basis for all science.

The artist’s representation of a black hole in “Our Universe.” [Image: Helmut K. Wimmer]

In many ways, the reason you and I are having this little blog conversation is precisely because astronomers know that black holes exist in Nature and are the central players in many astrophysical phenomena. But reading Gallant’s text it is clear that when he wrote Our Universe, the existence of black holes was still a subject of much debate among scientists. Today there are many ways that we have measured the properties of black holes and confirmed their existence, not the least of which are the many that have been detected via gravitational waves. But still, pictures of black holes remain elusive. The best we have so far is the Event Horizon Telescope picture, a silhouette of a black hole against the backdrop of stuff around it.

The picture in Gallant’s book is an attempt to show a black hole as a three dimensional object in real space, but how do you do that?  It was a noble attempt, and it is certainly not what a black hole looks like, but it served its purpose — it got my attention, it fueled my imagination, and it made me ask questions then go see if the answers were known. To this day I keep copies of Our Universe nearby — one in my office and one in my study at home. It is never far from my mind nor my fingertips, and I often pull it down and lose myself in the epic stories it tells.

The other thing I know happened to me in the fall of 1980 was my first exposure to Carl Sagan’s Cosmos. Starting in late September, every Sunday night, I sat rapt on my parents’ living room floor in front of the television, whisked away to worlds and places in the Cosmos I had only previously imagined, transported by the magic of film, the lilting and elegant soundtrack of classical music, and Sagan’s poetic and sonorous narrative. One of the most widely known episodes is Episode 9, “The Lives of the Stars” which famously begins with Sagan declaring, “If you wish to make an apple pie from scratch, you must first invent the Universe.”

Sagan uses his famous declaration about pies to introduce the concept of the chemical elements — the atoms from which all the beautiful and complex structures of Nature are built. Beyond the simplest elements — hydrogen and helium — very little was created when the Cosmos was born. Almost everything on the periodic table is created by stars during their lifetime, and a great deal of it (the heaviest elements) during the catastrophic death throes we call supernovae and gamma ray bursts. In telling us about the death of stars, Sagan uttered the magic words I had heard before — black hole. In his trademark penchant for poetic description, he called it “a star in which light itself has been imprisoned.”

Sagan’s Cosmos was the first place I was introduced to the ideas of black holes in the context of general relativity, beginning with masses curving space and affecting the motion of other masses, and also a discussion of the principles of black holes as tunnels [Images from Ep 9: “The Lives of the Stars”]

He had led us to the existence of the super-strong gravity of black holes through an imagined tea party with Alice and her friends in Wonderland, but then he hung on it all the modern picture of curved spacetime. It was, as far as I know, my first exposure to Einstein’s brilliant realization, and it has ever since dominated my destiny. Today, I have a doctorate in theoretical physics, earned for studying the magical mysteries of that self-same curved spacetime.

Me and J. Craig Wheeler. He’s one of the reasons you’re reading this blog right now!

For many of us, our interest in black holes might be piqued by these kinds of exposures, and then we go back to our lives as dental hygienists or soybean farmers or city managers. But this was all still swirling in my mind when I entered college, and in the true traditions of higher education, my exposures took those latent passions and exploded them into what would become my life. I was an undergrad at Oregon State University and at that time there was a stupendous class on campus called “Rocks & Stars,” run by the indomitable Julius Dasch. This was one of the most popular classes on campus, and had a regular stream of guest speakers who visited and talked to us about cool stuff.  I have strong memories of one visit from J. Craig Wheeler, a supernova expert from the University of Texas at Austin.

Supernovae are one of the pathways for making black holes in the Universe, and Wheeler gave us a spectacular talk that culminated with him reading to us from a science fiction book he wrote, called “The Krone Experiment.” I won’t give it away (go read it!) but what I remember from the talk was Wheeler talking us through what would happen if you were standing on a sidewalk and a micro-black hole came booming up out of the ground next to you. What would you see and experience? It’s the sort of question that just captures your brain and won’t let go. To be honest, it was the perfect question to ask a young scientist in the throes of deciding to commit their career to studying these enigmatic objects.

I think every one of these stories illustrates a key fact in my mind: it didn’t matter what I heard about black holes in my youth, only that I did hear about black holes. Exposure did what it should: it filled my head with all kinds of possibilities, all of them totally brain-melting, and made me pay attention and ask questions later.

This last point is the most important point here: we want people to ask questions. Either because they are confused, or because they are idly curious, or because they want to learn more. To that end, having mind bending movies like The Black Hole is stupendously important, and I don’t care if they get the science perfectly right! I have colleagues who often grouse about bad science in movies, complaining vociferously that the producers should have taken a basic science class, or gotten a good science advisor. They proclaim, “Is it really that hard to get the science right? The right science is just as cool!” 

But people aren’t watching The Black Hole to learn science (I certainly wasn’t) — they are being entertained, itching a part of their brain that wants to be asked “is that even possible or real?” And that serves its purpose, because eventually every one of them ends up in an audience somewhere at a public lecture and raises their hand and asks someone like me “is what happened in the movie real?”  THAT is where we get the science right. The movie’s job was to put a question in someone’s mind, to make them care enough to know what the right answer might be, and then in some other part of their lives have some discussions about science, what is known, what is not known, and what the other mysteries of the Cosmos might be.

————————–

This post is the last in a series about black holes.

Black Holes 01: Imaging the Shadow of Darkness

Black Holes 02: What are black holes made of?

Black Holes 03: Making black holes from ordinary stuff

Black Holes 04: Singularities, Tunnels, and Other Spacetime Weirdness

Black Holes 05: Inklings & Obsessions (this post)

Black Holes 1: Imaging the Shadow of Darkness

by Shane L. Larson

Of all the phenomena in the Cosmos, black holes evoke a special sense of wonder in most people.  What is it that captures the imagination when you hear the words “black hole?  There are countless mysterious and exotic astronomical phenomena that pique the interest of astronomers, but few of them have the evocative power over people’s imaginations that black holes do. 

There is no known portrait of the Reverend John Michell.

What are we talking about? By definition, a black hole is an object whose gravity is so strong, not even light can escape. The first person to imagine such an object was the Reverend John Michell in 1783. At the time, it was an interesting supposition since the speed of light was known to be “fast,” so such an object’s gravity had to be “strong,” but there was nothing inherently special about the speed of light itself. The same idea was later promoted quite widely by Pierre-Simon Laplace (he had a much better press machine behind him than the Reverend Michell). But the exoticness of black holes was not fully realized until the early 1900s, when two things happened.

There is an ultimate speed limit in the Universe!

First, in 1905, Einstein published special relativity and the scientific community rapidly tested many of the ideas and found them to be consistent with the behaviour of everything in Nature. The central tenet of special relativity, which is of paramount importance to our discussion here, is that there is an ultimate speed limit in the Cosmos, somehow built into the foundations of the structure of the Universe: you cannot travel faster than the speed of light. People often ask me, “what’s so special about the speed of light?” There is nothing special about light, there is something special about the speed. It happens that light was the first thing we ever discovered that can travel at the ultimate speed limit, so we call it “the speed of light.” The proper statement is really, “nothing can travel faster than the ultimate speed limit!

Second, in 1915 Einstein published general relativity, which showed how to think about gravity in a way that was consistent with special relativity. Less than a month later, Karl Schwarzschild found the first astrophysical solution to the equations of general relativity, what we today call a Schwarzschild black hole. This is a perfectly spherical black hole, an object whose gravity is so strong you have to exceed the ultimate speed limit to get away from it. Extraordinarily, but perhaps not surprisingly, the size of Schwarzschild’s black hole is exactly the size predicted by Michell in 1783.

At this point, we can begin to understand why black holes are so exotic and alluring. It’s not just that they have intense gravity. It’s that they are inescapable. If you have the sad misfortune to fall in one, you will never be able to get back out (we’ll talk about “tunnels” through black holes in a later post). That very idea of being trapped forever, incontrovertibly prevented from leaving by the laws of Nature — that’s mind boggling, and clashes with our normal sense of free-will. It very definitely has a “Nature is more dangerous than we suppose” air about it that we often only reserve for documentaries about sharks, the wild savannas of Africa, and just about all the wildlife in Australia. 🙂

It is the inescapable Nature of black holes that makes them interesting to think about, but it is also what makes them hard to study in astronomy. All things being equal, black holes are just about the hardest cosmic phenomena to observe because, for the most part, we study the Universe using light. By definition black holes emit no light! Recently, our burgeoning ability in gravitational wave astronomy (here are all the posts at writescience tagged “gravitational waves”) gives us a way to probe black holes directly, allowing us to understand them as single, big objects — how massive they are, how fast they might be spinning, what processes might form them. But trying to understand what is happening up close to the black hole, where the gravity is at its most intense and unusual things can happen, that’s hard. We would really like to know what happens if you are as close as possible to the black hole without being trapped, down near the surface of last escape, a place called the “event horizon.” Probing this region is the goal of one of the most ambitious projects in astronomy, called the Event Horizon Telescope.

With telescopes, we always observe light emitting objects, and watch what happens to them in the vicinity of black holes.  We use these observations as a way to understand the properties of black holes and what they are capable of doing to the Universe around them. Most of the time when you hear about black hole discoveries, this is what has happened — something did something weird near a black hole, and told us the story with light! For instance, at the centers of most large galaxies astronomers find massive black holes, millions or billions of times more massive than our Sun. The one in our own galaxy is called Sgr A* (pronounced “Sagittarius A-star”). Since the 1990s, astronomers have been watching stars down in the center of the galaxy, and have now watched them long enough to see them move across the sky and make closed round paths — orbits! Something you may remember from your early exposure to astronomy is that whatever is at the middle of an orbit is the source of gravity that makes and object go around in its orbit… and at the centers of these stellar orbits we don’t see anything. The size of the stellar orbits, and the speed they move, tells us that whatever is there has four MILLION times the mass of our Sun. There is no known dark phenomena in Nature that can be that tiny, that massive, and create that much gravity other than a black hole.

Two decades of observations have shown the orbits around the 4 million solar mass black hole at the center of the Milky Way. [NCSA/UCLA/Keck]

About 53 million lightyears away, in the direction of the constellation Virgo, there is a massive galaxy known as Messier 87, which can be easily seen with backyard telescopes. It has always been an object of intense interest, even before we knew there were other galaxies besides the Milky Way. In particular, in 1918, Heber Curtis, observing with the 36-inch Crossley Telescope at Lick Observatory noticed “a curious straight ray… apparently connected with the nucleus by a thin line of matter” (read a copy of Curtis’ original paper here). Today we call such structures “jets” and know they are powered by matter interacting with black holes. In the century since Curtis’ first observation, many observations of the M87 jet have been made and used to understand the properties of the black hole that drives it.

The black hole in the center of M87 powers an enormous, energetic jet of material spewing out from the galactic core. (L) We think we were one of the first amateurs to image this jet in 2001 [Image: S. Larson/M. Murray/A. Block] . (R) HST image of the jet, for comparison. [Image: STScI/Hubble/NASA] 🙂 [Click to embigen!]

The Event Horizon Telescope takes this observing strategy to the next level. The goal is to look as close as possible to the event horizon, and see what can be seen, down near the root of the jet. Can matter glowing brightly before falling into the event horizon be seen? Can light from stars and matter behind the black hole be bent by the black holes intense gravity and provide a lensed silhouette of the black hole? To even think about doing a project like this, you have to know two things: (1) how big on the sky does a black hole appear, and (2) what is the tiniest object in the distance that a telescope can see?

The apparent size of an object in the sky depends on how intrinsically big it is, and how far away it is.  For black hole sizes, we can use the size predicted by Schwarzschild to get a sense for their diameter.  If you want to tinker and get out your calculator, the diameter of a Schwarzschild black hole is given by the formula

where dbh is the diameter of the black hole, Mbh is the mass of the black hole, G is Newton’s gravitational constant, and c is the speed of light. If you put in the mass of any black hole in kilograms, then this formula tells you the diameter of the black hole in meters.  A black hole the mass of the Earth has a diameter of just over 1.5 centimeters. A black hole the mass of Neptune has a diameter just a bit bigger than a human head.  A black hole with the mass of the Sun has a diameter of almost 1500 meters (just under a mile). As the mass of the black hole gets larger, the diameter gets larger.  So consider the two black holes we’ve discussed above: Sgr A* and M87.

A black hole with the mass of the Earth is about the size of a marble. A black hole with the mass of Neptune is about the size of your head! [Image: S. Larson]

Sgr A* is 4 million times the mass of the Sun, and has a diameter of 23.6 million kilometers — more than 60 times the size of the Moon’s orbit! The black hole in M87 is even larger. Massing in at 3.5 billion times the mass of the Sun, it has a diameter of 20.7 billion kilometers, or about 3.5 times the size of Pluto’s orbit! If you plopped the M87 black hole down on the Solar System, every planet and world NASA has ever explored would be inside the black hole; of all things human, only Voyager 1 would escape, sitting just outside the event horizon.

So, what does it take to observe the Cosmos on the scales of even big black holes? Telescopes can make out things that appear very small in the sky, but how small? How big something appears depends on how far away it is. Imagine you have a friend holding a beach ball and a dime, standing at the far end of a field. In all likelihood, you can see the beach ball, but not the dime. The beach ball appears tiny, but from far away a larger object is easier to see than a smaller object. A telescope’s ability to distinguish the size of objects in this was is called its resolving power, and depends on the color of light you are using (technically, the wavelength) and the effective diameter of your telescope — the bigger the telescope, the better resolving power it has.

How large an object looks to you depends on its size and its distance. Here, you see when Michelle is very far away you can still make up the larger ball, but the smaller coin is harder to see! [Image: S. Larson]

The idea of the Event Horizon Telescope is to look for big black holes because they will have a discernible size even if they are far away. The targets of interest are the black hole at the center of our own galaxy (Sgr A*) and the black hole at the center of a M87. Both of these black holes have a size on the sky of a little more than a billionth of a degree. How big is that? Well, Sgr A* covers the same size on the sky as a quarter that is about 2/3 of the way between the Earth and the Moon. The M87 black hole covers the same size on the sky as a quarter that is about 1.5 times the distance of the Moon. Those are really small, but you and I live in the future — our telescopes are up to the task.

To make the measurement, the Event Horizon Telescope team uses radio telescopes spread across the Earth, all observing simultaneously as if they were a single giant telescope the size of the planet. This kind of astronomy is called VLBI — Very Long Baseline Interferometry. The resulting picture of M87, the first released by the Event Horizon Telescope, is shown below — a brilliant ring of light, surrounding the shadow of a massive black hole, the first of its kind.

The first picture of the black hole at the heart of M87, formed by light being bent around the inner most regions of space outside the event horizon. The teams measurements show the black hole is heavier than previous measurements, totaling almost 6.5 billion times the mass of our Sun. [Image: Event Horizon Telescope Collaboration]

This is the first time we’ve been able to accurately reconstruct a picture using light from all the small areas around a black hole, effectively imaging for us the shape and size of the event horizon. It is a tremendous leap forward and provides us a new and important way to probe black holes and their properties. As with all enigmatic things we see happen in the Cosmos, the more ways we have of measuring them, the easier it is for us to figure out what is going on!

And this is just the beginning!

————————–

This post is the first in a series about black holes.  The complete series of posts is:

Black Holes 01: Imaging the Shadow of Darkness (this post)

Black Holes 02: What are black holes made of?

Black Holes 03: Making black holes from ordinary stuff

Black Holes o4: Singularities, Tunnels, and Other Spacetime Weirdness

Black Holes 05: Inklings & Obsessions

————————–

For a great video describing the intricate details of the light interacting with the black hole to make images, check out this excellent video from the team over at Veritasium:

Memento Mori 1: Slip the Surly Bonds of Earth

by Shane L. Larson

From January 27 to February 1 every year is a time of remembrances at NASA: it is the week where we observe the anniversaries of the deaths of three flight crews, all of whom perished in the pursuit of human spaceflight. We remember and celebrate the the fallen crews of Apollo 1, Challenger, and Columbia.

From just an altitude of 30 km, the view of the Earth is different — a planet against the void of space. Once the domain of astronauts, views like this can be obtained with balloons and simple digital technology. [Image: S. Larson & HARBOR Program at Weber State University]

Humans often think of themselves as invincible, as the apex species on planet Earth, but it seems clear that we are more fragile than we like to think. If you take our frail bodies and carry them just 50 miles over our heads, we cannot possibly survive on our own. But we are a curious and clever species, and not prone to accepting the notion that there is something we cannot do. Over the long course of our history, we have harnessed technology to allow us to take our bodies to places they were not designed to go, and to survive. It’s easy to discount our earliest endeavours as mundane: constructing shelters, building fires, and making clothing that permits winter wandering. Such skills ultimately transmuted from simple survival into dreams of mimicking the abilities of other lifeforms. Could we dive deep beneath the waves, or take to the air and fly?

Humans are good at walking the long road to making their bodies do things never intended for. (L) Early diving suits, used to explore the sunken Lusitania in 1935. (R) Samuel Langley’s Aerodrome was an early attempt to construct a powered heavier than air flying machine, prepping for launch test in 1903. [Images: Wikimedia Commons]

By the 1800s, aeronauts had successfully developed ballooning, and by the early 1900s the development of mechanical wings and controls launched the era of human flight that has evolved into the aviation industry we have today. But in the middle of the 20th century other dreams were simmering to the surface, largely in the minds of fiction authors. What would it be like to travel beyond the bonds of Earth? Could we make a remarkable voyage from the Earth to the Moon?

Historians and cultural specialists often frame the conversations about the dawn of the Space Age around the Cold War, the opposition of East versus West in the aftermath of World War II. The Soviet Union and the United States were engaged in a war of ideologies, marked by strutting and preening. Technical achievements trumpeted how each ideology supported progress more, and reaching the Moon was the ultimate prize.  But while the national agenda may have been set that way, and resources committed to the endeavour, that is not what won people’s hearts and minds. Consider all the scientists and engineers who designed and built the great machines, the astronauts who flew in them, and the millions who watched from the sidelines: I’m willing to speculate that only a handful of them were motivated by politics. Far more of them, I think, felt the rapture of the all encompassing dream of reaching out from our small island home, the Earth.

Carl Sagan once noted that knowing the Cosmos is a humbling and character-building experience. Our conceits let us dare leave the Earth, even in the face of a Universe infinitely harsh and relentlessly brutal and unforgiving in ways that are hard for us to imagine. Our successes are soaring, exultant moments that we point to in later days, reminding ourselves of what we are capable of. But the failures, the disasters, are that much more crushing, reminders of how hard our goal is to attain, reminders of how painfully incapable and inexperienced we are in the quest to crawl out of our cradle.

The loss of the NASA flight crews were singularly painful moments — it is impossible to imagine the loss felt by their families, or by their colleagues and friends at NASA who had worked alongside them to make their journey possible. But for the rest of us, who watched the tragedy unfold on smaller than life television screens and brittle leaves of newspapers, those moments are burned in our memories, surrounded by the other parts of our lives we were engaged in that day.

The loss of Apollo 1 occurred just twelve days after the first Super Bowl, where the Green Bay Packers beat the Kansas City Chiefs, 35-10 in the Los Angeles Coliseum. The Vietnam War was still raging and arguably occupied a huge part of the American psyche, dominating the news every day.

The Apollo 1 crew. Left to right: Gus Grissom, Ed White, and Roger Chaffee. [Image: NASA]

On 27 January 1967 (25 days prior to launch) Gus Grissom, Ed White, and Roger Chaffee — the first three person crew in the history of the Space Age — mounted the gantry at launch pad 34 and at 1pm Eastern Standard Time entered the Apollo 1 capsule for their “plugs out test.” Plugs out was a regular ground test NASA ran to assure themselves the spacecraft could operate on its own without being plugged into power and equipment here on planet Earth. After five-and-a-half hours of tests, the crew was still in their capsule, sealed inside and trouble-shooting problems (notably a problem with the communications link). At 6:31:04.7 pm fire broke out on the capsule and a garbled alarm to that effect was called out by one of the astronauts. The fire was fueled by the pure oxygen atmosphere in the capsule, and just 15 seconds passed before the hull of the capsule ruptured at 6:31:19 pm. It took pad crews more than five minutes to get inside the capsule to the crew, who had perished.

It was a horrific tragedy. Later analysis and investigation showed exactly how it happened and what prevented the crew from escaping and rescue crews from getting to them more readily. It was caused, as Apollo 8 Commander Frank Borman later remarked, “by a failure of imagination.” NASA was not unaware of the dangers associated with spaceflight, nor were the astronauts. But up to that point, they had failed to imagine that a regular test on the ground could lead to the death of a crew.

There was an investigation, and Congressional hearings. There are plenty of machinations about why such investigations happen, but I think they happen for a very particular reason — to allow us to understand where we (those left behind) failed those we lost. We often reflect, particularly in the heat of our pain, on whether or not the loss of human life is an acceptable risk in our quest to go where Nature never intended. Gus Grissom himself had weighed in on such risk the year before he perished:

If we die we want people to accept it. We are in a risky business, and we hope that if anything happens to us, it will not delay the program. The conquest of space is worth the risk of life. Our God-given curiosity will force us to go there ourselves because in the final analysis, only man can fully evaluate the moon in terms understandable to other men.

Eventually, the Apollo program restarted, leading to six successful landings on the Moon between 1969 and 1972. The Space Age waxed on, and there were other close calls — nail biting moments when it seemed we might lose another crew — but NASA, with a flotilla of capable engineers and scientists, weathered them all and brought the crews home.

The Challenger crew on walkout. Front to back: Dick Scobee, Judy Resnick, Ron McNair, Mike Smith, Christa McAuliffe, Ellison Onizuka, and Gregory Jarvis.

That changed on 28 January 1986, with flight STS-51L and the space shuttle Challenger. It was the 25th mission of the space shuttle program, and Challenger’s tenth flight. The mission had garnered far more attention from the public than many of the previous flights because of the unique nature of its crew — it was the first flight to include a crew member for the “Teacher in Space” program, Christa McAuliffe. Her inclusion on the crew had electrified students, teachers, and schools across the country, and on the morning of the launch millions of people were glued to their television screens. I was among them, huddled around a large TV screen in our school library with a group of friends.

Launch of Challenger on STS 51L. [Image: NASA]

After three previous scrubbed attempts, and a delay of two hours that day, Challenger launched at 11:38am EST on 28 January 1986. Just 73 seconds into the flight, a small leak in the right solid-rocket burned through a support strut and into the main external fuel tank, leading to a catastrophic failure, and loss of the entire crew: Dick Scobee, Mike Smith, Ron McNair, Judy Resnick, Ellison Onizuka, Christa McAuliffe, and Gregory Jarvis.

It was a devastating moment indelibly etched in the minds of everyone who had been watching. As with Apollo 1 before it, the brought the American spaceflight program to a standstill for 975 days. A six month investigation following the disaster identified a failed O-ring in the solid-rocket as the source of the failure, enabled by poor risk analysis and abetted by colder than normal temperatures that did not delay the launch on the day of the accident (though it should have).

The Challenger crew portrait. L to R: Ellison Onizuka, Mike Smith, Christa McAuliffe, Dick Scobee, Greagory Jarvis, Ron McNair, and Judy Resnick. [Image: NASA]

The loss of Challenger was particularly overwhelming because it was the largest crew ever to perish on a mission — 7 people, most of them civilians or civilian astronauts, not test pilots or military pilots. For all of us with day jobs as teachers, or 7-11 managers, or grocery clerks, or dental hygienists — it put a very real face on the fact that if we ordinary people ever travel to space regularly, there will be undeniable catastrophes that occur. Such realizations dramatically dampen the spirit and enthusiasm for daring greatly.

But the space shuttles did return to the skies, once again, just more than two-and-a-half years later, when the Discovery soared aloft with a 5 person crew for a four day flight. Space shuttle missions continued on apace again, the flights once again fading in the news cycle and noted only by those who were paying attention or soaring alongside in their mind’s eye.

After the Challenger disaster and return to flight the shuttle program had many successes, including visiting Mir, laying the groundwork for the International Space Station. [Image: NASA]

After the loss of Challenger a new orbiter, Endeavour, was commissioned and joined the other shuttles, Columbia, Discovery, and Atlantis. There were 88 more shuttle flights through the start of 2003, beginning with STS-26 by Discovery. There were spectacular successes all along the way, including the launch of space probes like Galileo and Ulysses. The space shuttles deployed the first two of NASA’s “Great Observatories,” the Compton Gamma Ray Observatory and the Hubble Space Telescope. The shuttle began visiting the Russian Space Station, Mir, and assembly began on the International Space Station. Other satellites were launched, and the Hubble Space Telescope was serviced and repaired. In a way, the space shuttles accomplished in that era what NASA had always promised — spaceflight had become common, an everyday experience. Seeing news of the shuttle launching on the backpage of the newspaper was kind of like seeing a story about the latest fleet of city buses or the bio of a new city manager. Spaceflight faded into the background cacophony of modern life.

The Columbia crew portrait. L to R: David Brown, Rick Husband, Laurel Clark, Kalpana Chawla, Michael Anderson, Willie McCool, and Ilan Ramon. [Image: NASA]

But in early 2003, the space shuttle Columbia launched on a 16 day mission, STS-107. The 15-day mission carried out a wealth of experiments. The carbo-bay held the Spacehab module, which provided additional habitable space for the experiments of crew, beyond the space available on the orbiter itself. Prominent experiments included video monitoring and characterization of atmospheric dust, as well as monitoring the web-building habits of orb weaver spiders in microgravity. At the end of the mission, on 1 February 2003, Columbia had reentered the Earth’s atmosphere heading for a landing in Florida. Undetected damage Columbia had sustained on the forward edge of the left wing during launch would be its undoing. During reentry, the damage allowed hot atmospheric gases to enter the airframe, burning through the wing and leading to a catastrophic breakup of the orbiter, killing all seven crew aboard: Rick Husband, William McCool, Michael Anderson, David Brown, Laurel Clark, Kalpana Chawla, and Ilan Ramon.

This has always been my favorite picture of the Columbia crew, the way I’ll always remember them. L to R, Front — Kalpana Chawla, Rick Husband, Laurel Clark, Ilan Ramon. L to R, Back — David Brown, William McCool, Michael Anderson. [Image: NASA]

After the Columbia tragedy, the burden of returning to the skies once again fell to Discovery. Once again, return to the skies we did. On 26 July 2005, Discovery launched on STS-114, carrying a 7 person crew on a 13 day mission to the International Space Station. After the Columbia tragedy, there were 22 shuttle flights, but on 8 July 2011, Atlantis made the last space shuttle launch in history. When its wheels rolled to a stop in the cool morning hours of 21 July 2011 at the Cape, the era of space shuttles came to an end. The shuttles have retired, and like their capsule forebears, have retired to museums and science centers around the country where you can visit them, stare at them, and relive the adventurous journeys they made.

The space shuttle orbiters, now decomissioned, can be visited at various museums around the country. Discovery, responsible for two Return to Flight missions, after the Challenger and Columbia losses, can be visited at the Udvar-Hazy branch of the Smithsonian Air and Space Museum. [Image: S. Larson]

It should be noted that spaceflight is inherently dangerous; fatalities were not confined to the American space program — our nominal competitors in the Space Race, the Soviet Union, also suffered great losses. In 1967, cosmonaut Vladimir Komarov died on Soyuz 1, when the parachute failed to properly deploy on return to Earth; it was the first in-flight fatality of a spacefarer. In 1971, cosmonauts Georgy Dobrovolsky, Viktor Patsayev, and Vladislav Volkov were the first crew to spend time aboard a space station, living for 23 days aboard Salyut 1. They died returning to Earth after an accidental decompression of their capsule; they are the only crew to have died in space.

Today, the human spaceflight program is quieter than it once was. The United States currently does not have a launch system for sending crews to space, though American astronauts travel to the International Space Station aboard Russian rockets. That does not seem to dampen the enthusiasm for nor the mystique of astronauts!

Hero culture is a thing, and it isn’t always a good thing. Joseph Campbell, in his excellent book “The Power of Myth” says that “I always feel uncomfortable when people speak about ordinary mortals because I’ve never met an ordinary man, woman or child.” In general, I think there is deep truth in that. But astronauts are something different: almost universally, they encapsulate what can be good about hero culture. We watch and look up to astronauts the way many of us look up to our parents or our grandparents — as a source of inspiration, a source of motivation, as proof that we can and will be more than we think. Every day, we all do something in the world that matters, but we forget that, crushed under the press of noise from the news, or burdened by the weight of difficulties with our co-workers, our families, our social lives, or making enough money to survive. In some corner of our minds, we aspire to be more. We clamp down on that bright spark of aspiration, perhaps embarrassed by it, and seldom let it shine. Instead we only uncover it when we’re alone at night, gazing at it and daydreaming in the moments before sleep. Our heroes, whomever they are, are a spark we revel in, when we are willing to let it leak out.

For me, space has ever-infused my thoughts and dreams. Every time I see an astronaut spacewalking with the jeweled curve of the Earth reflected in their visor, or watch the long loping hops of the Apollo astronauts on the Moon, or look at the photographs of our lost crews, I still somehow imagine my face among them. Which is weird, because I long ago gave up the quest to be an astronaut, replacing it with other dreams of space in the forms of black holes, surging gravitational forces, and galaxies billions of lightyears away. Despite abandoning the quest, apparently I didn’t abandon the dream. This week every year always shows me that. Revisiting the fallen NASA crews every  year makes me remember what it is about human spaceflight that moves us so.

Kalpana Chawla.

And so, as this week concludes and passes us by once again, I encourage you to dust off your mental photo-album of your heroes and refresh your soul with them once again. For those who are still with us, embrace their vision and mission anew, and go out refreshed in your fight to make the world a better place. And for those who have left us, say farewell once again, to whomever they are. They are the ones that remind all of us that in our brighter moments, we strive to be something better, that we are more than the tribulations in our every day lives may suggest we are. Remember those brighter moments, and stretch for them every day. Kalpana Chawla reminds us, “The path from dreams to success does exist. May you have the vision to find it, the courage to get on to it, and the perseverance to follow it.”

And so, to the fallen crews whose gossamer memories drift in the back of my mind, I say farewell once again. Gus Grissom. Ed White. Roger Chaffee. Vladimir Komarov. Georgy Dobrovolsky. Viktor Patsayev. Vladislav Volkov. Christa McAuliffe. Gregory Jarvis. Judy Resnick. Dick Scobee. Ron McNair. Mike Smith. Ellison Onizuka. Kalpana Chawla. Rick Husband. Laurel Clark. Ilan Ramon. Michael Anderson. David Brown. William McCool.

From the stars we came, and to the stars we shall return, now and for all eternity. Ad Astra Per Aspera.

=========================

This post is the first post in a series that explores the ephemeral nature of human life in our quest to understand our place in the Cosmos. The posts in the series are:

The Cosmos in a Heartbeat 3: The End is Just the Beginning

by Shane L. Larson

The fence we walked between the years
Did bounce us serene.
It was a place half in the sky where
In the green of leaf and promising of peach
We'd reach our hands to touch and almost touch the sky,
If we could reach and touch, we said, 
'Twould teach us, not to ,never to, be dead.
We ached and almost touched that stuff;
Our reach was never quite enough.
If only we had taller been,

Ray Bradbury.

So opens Ray Bradbury’s epic poem, “If Only Taller We Had Been…” He had composed it for a panel discussion on 12 November 1971, just before Mariner 9 arrived at Mars, becoming the first spacecraft to ever orbit another planet (here’s a video of Bradbury reading the poem). Bradbury’s poem is an ode of optimism to the future — smiling gently at our ancestors and their grasping reach which didn’t quite reach us on the first try. It is a grand hope for our posterity that they achieve all that we dare to dream. The future is a murky place, fraught with unknown difficulties and challenges, but illuminated by desire and ambition.

Despite the long years that remain between today and tomorrow, you can image what our future selves might do in our quest to understand the Cosmos. The Universe will not change much between now and then, but our understanding of the Universe will change, and change dramatically.  The specific details we cannot know, but we know where the limits of our knowledge are, and we know what the capabilities of our current science experiments are. Scientists already are planning for the future, imagining, designing, and developing the Great Machines of tomorrow.  Let’s spin the clocks forward 30 years and take a glimpse of what we expect.

How my best friend imagines my future personal telescope might be like. [Image: J. Harmon]

In 2048 it is impossible to know what sorts of telescopes amateurs will have. But if history is a teacher, amateurs will have access to bigger telescopes and better technology for capturing light from the sky, whether it be cameras or spectroscopes, or automated robotic mounts, or telescopes that see in light our eyes cannot see. A few amateurs already have such capabilities, and the future will surely make such technology more accessible.

Professional astronomers are also looking ahead toward their next generation of telescopes. On the ground, the next generation of telescopes will be about thirty meters in diameter, three times larger than the current generation and six times larger than the venerable Hale Telescope at Mount Palomar. Thirty years from now, Hubble will be long gone, but its successor, the James Webb Space Telescope (JWST), will have been lofted in its place. Right now, JWST is expected to launch in 2021. It should cast its gaze on the Unvierse for a decade or more, depending on how long its fuel reserves last. As with Hubble, it will see farther and see more than any telescope in history, though we don’t yet know what new things it will teach us. It is a marvel of engineering, designed to fold up and fit inside a rocket for launch, it will unfold like a flower when it arrives in space — 18 hexagonal segments that together comprises a gigantic 6.5 meter diameter mirror that looks out on the Cosmos, all of it sitting in the shade of a multi-layered sun-shield the size of a tennis court. If JWST has a tenure as long and as lustrous as the Hubble Space Telescope’s, then the discoveries in store for us will be extraordinary and transformative for astronomy.

The James Webb Space Telescope (JWST) will be more than two and half times the diameter of Hubble, it’s mirror comprised of large hexagonal segments. [Image by Paul Kalas]

Space affords many opportunities to expand our view of the Cosmos, and this is certainly the case in gravitatioanl wave astronomy. In the early 2030s, the European Space Agency and NASA are planning to launch a gravitational wave observatory called LISA — the Laser Interferometer Space Antenna. It will operate continuously for a decade or more, well into the 2040s, probing new and exotic phenomena, many of which can only be understood or detected at all with gravitational waves. 

LISA will be a triangular constellation of spacecraft separated by 2.5 million kilometers, following the Earth around in its orbit. [Image: S. Barke]

Like its ground-based cousin, LIGO, LISA is a laser interferometer. It shines lasers back and forth between mirrors, timing how long it takes the laser to make the flight. Small changes in that flight-time, changing in regular undulating patterns, are the hallmark of gravitational waves. So what’s so different about LISA?  LISA is about a million times larger than LIGO, which is why it has to be in space. The reason it is so much larger is that the size of a laser interferometer determines the sources of gravitational waves it can detect.  Whereas LIGO can detect small stellar skeletons in the last moments of their lives, as they whirl around each other hundreds or thousands of times a second before colliding, LISA is sensitive those same stellar skeletons when they are much farther apart, earlier in their lives when they speed around their orbits only once every thousand seconds or so. Whereas LIGO can detect black holes that have a few to a few tens times the mass of the Sun, LISA can detect black holes that are millions of times the mass of the Sun (“massive” black holes, like the one at the center of the Milky Way).  Astronomers say that LISA observes a different part of the gravitational wave spectrum. Just as we have different kinds of “light” telescopes (optical telescopes, radio telescopes, x-ray telescopes), we have different kinds of gravitational-wave “telescopes” (LISA, LIGO, and others).

So what will LISA teach us about the Cosmos? Consider the Milky Way. Like many galaxies, the Milky Way is ancient — 10 billion years old. Comprised of 400 billion stars, many stars in the Milky Way have lived their lives and passed on into the stellar graveyard over the long course of its history. Something you may remember from your astronomy learnings is that many of the stars in the galaxy are not single stars, but binary stars — two stars orbiting around each other the way the Moon orbits the Earth or the planets orbit the Sun. That means when both stars die, their skeletons sometimes stay together, orbiting each other over and over and over and over again. The stellar graveyard is full of not just skeletons, but binary skeletons, and in particular binary white dwarf skeletons.

White dwarfs are the size of the Earth, but the mass of the Sun. When they are separated by roughly half the Earth-Moon separation, they emit gravitational waves LISA can detect. [Image: NASA/Chandra X-Ray Center]

A white dwarf is a particular kind of stellar skeleton, created when an ordinary star reaches the end of its life. Most stars — and our Sun is among them — are not heavy enough to explode upon their deaths. Instead they swell up into a red giant, then compress themselves down into a skeletal remnant of their former selves, about the size of the Earth. These white dwarfs are hot and crystalline, mostly comprised of carbon, and will over the remaining history of the Universe slowly cool and fade. Most stars in the Milky Way are ordinary, average stars like the Sun. That means that most of the stellar skeletons in the Milky Way are white dwarfs, created over the ten billion history of the galaxy. All told, there are some ten to fifty million white dwarf binaries, and all of them are going to be emitting gravitational waves that LISA can see. 

A simulation of the stellar graveyard of the Milky Way. [Data by K. Breivik and S. Larson]

Part of preparing for astronomy in the future is imagining what you might observe and discover. We simulate the entire life history of the Milky Way on the computer and ask what does the stellar graveyard look like. Where are the white dwarfs, where did they come from, and what do they tell us about the life and history of stars in the Milky Way? When faced with a view of our home galaxy like this, and you imagine all the vast cacophony of gravitational waves from the stellar graveyard? We often describe this as the “lunch-room problem” or the “party problem.” Imagine you are hanging out in the cafeteria or a crowded restaurant at lunchtime. Everyone there is talking, and what you hear is a dull rumble of noise coming from every direction in the room. You can tell it is people talking and laughing, but by and large all of the sound is mixed together and most of the conversations are indistinguishable from one another. Astronomers call this “confusion noise.” Of course you can hear some conversations. You can hear people that are close to you, and you can hear loud people, even if they are far away. You can always hear these close or loud people, no matter what the background noise is. Astronomers call signals that stand out above the confusion “resolved sources.”

Your ears, and mostly your brain (based on what your ears are telling it), are fully capable of separating resolved sources from confusion noise — you do it every time you go out to eat!  Our job as future gravitational wave astronomers will be to teach computers how to carefully pour over the LISA data and learn to separate resolved white dwarf binaries that are close or loud. Out of the tens of millions of confused skeletons in the stellar graveyard, tens of of thousands will be resolved and studied by LISA. Encoded in that collection of stars are the tales of how stars like the Sun have lived out their lives, and a deeper understanding of how the birth and death of stars has surged and waned over the long history of the galaxy.

Dead stars aren’t the only thing that LISA will observe; it will also be sensitive to black hole binaries — massive black hole binaries. One of the great astronomical discoveries astronomers have made in the last few decades is that big galaxies harbor massive black holes at their centers, black holes of millions or billions of solar masses. As our telescopes have gotten larger and able to see deeper into the Cosmos, we have also started cataloging galaxies in all their shapes and forms, and discovered that sometimes they collide. So what happens when two galaxies, each harboring a massive black hole, collide? 

There are many known examples of colliding galaxies, but this is a personal favorite — the Rose and Hummingbird (Arp 273). The smaller galaxy is throught to have already passed through the larger galaxy once. [Image: Hubble/STScI]

Their stars swarm and merge like a cloud of angry bees, eventually coalescing due to their mutual gravitational attraction and form a new galaxy. Their big black holes slowly sink to the center, where they find one another and begin a slow, spiraling orbit that grows ever shorter as time goes on. When the orbits take only 10,000 seconds or less, they become observable by LISA.

Today, we know galaxies merge, but we know little about the processes that help massive black holes grow. Do they accrete gas? Do they grow by absorbing stars over and over again? Or do they only grow by merging with other black holes? LISA’s observations of massive black holes, together with where in the Cosmos they are found, will begin to provide answers to those questions.  We don’t know those answers today, because we’ve seen that galaxies collide but have yet to see massive black holes merge. In lieu of LISA data, which is still more than a decade in the future, we simulate different ways to grow galaxies and black holes on super-computers, and simulate what LISA would observe.

One massive simulation, spanning the entire age of the Universe, is called the Illustris Simulation. The movie below is a visualization of the Illustris simulation from the Big Bang to the present day. The simulation accounts for gas and dark matter int he Universe, and tracks the formation of stars, galaxies, and black holes across Cosmic time. We use the simulation as a model for the actual Universe, and “observe it” with a simulation of LISA. What do we learn from this? That the sky is going to be alive with massive black hole binaries, visible to LISA in every direction and all the way to the edge of the Observable Universe. In the movie below, we show all the mergers that would be detectable by LISA if it were flying at the right times (data simulation be Michael Katz and S. Larson).

You can imagine, and rightfully so, that all the massive black holes just add to the confused cacophony of gravitational waves created by the millions of white dwarfs in the galaxy. The Cosmos is full with the gravitational chorus, and our job as astronomers is to pick out all the melodies, and harmonies, and individual instruments and voices that make it up.

The miracle of the modern age is that we are suddenly aware that the Universe is sending us messages with a multitude of signals — light, particles, and gravitational waves. It’s an intricate, interlaced story that we are just now learning to interpret. Modern, instrument based astronomy began with the invention of the telescope some 400 years ago. Particle astronomy is only 100 years old, and gravitational wave astronomy has only been successful in the last five years. Our ability to probe the Universe carefully and precisely has existed for only the bareest fraction of Cosmic time — a heartbeat in the life of the Cosmos. We’ve used our ingenuity, our curiosity, and our creativity to spin that short experience into a complex and increasingly sophisticated understanding of the nature of the Universe, and our place within it.

=========================

This post is the last of three based on a talk I have given many times over the last few years, updating it each time to reflect the latest coolest things. The complete set posts of the series are:

The Cosmos in a Heartbeat 1: A Love Affair with the Cosmos

The Cosmos in a Heartbeat 2: Coming of Age

The Cosmos in a Heartbeat 3: The End is Just the Beginning (this post)

This post was enabled by a new version of the talk done as a Kavli Fulldome Lecture at the Adler Planetarium in Chicago. The talk was captured in full 360, and you can watch it on YouTube here. If you have GoogleCardboard, click on the Cardboard Icon when the movie starts playing; if you watch it on your phone, moving your phone around will let you look at the entire dome!

I would like to thank all my colleagues at Adler who worked so hard to translate what was in my brain into a story told in the immersive cradle of the Grangier Sky Theater. The talk was given on 9 Nov and 10 Nov 2018.

Beyond the Earth

by Shane L. Larson

I suspect that most of you reading this are just like me — you’re an ordinary citizen of Earth, and have never been to space. Never-the-less, we know a lot of facts about space, the most important of which is it is an inhospitable environment that would kill every one of us cold dead if we didn’t have the technology to protect ourselves. Do you ever wonder how we know that? Sure, the world’s space agencies have sent astronauts to space, but how did they know what to expect when they got there? The answer to that question hides one of the most magnificent truths of the Cosmos we have learned: that the Cosmos is knowable and through pure happenstance we as a species have discovered that secret. We can use the simple tools of our senses, together with a few brain cells, to unveil the machinery of Nature.

Collier’s, February 1953.

I started thinking about this because of this magazine cover. In February 1953, the launch of Sputnik and the beginning of the Space Age were still 4 years and 8 months away. The launch of Yuri Gagarin, the first human to fly into space, was still 8 years and 2 months in the future. But the cover of Collier’s magazine boldly showed an image of that future, and the future was bundled up in a spacesuit.

The need for spacesuits was, perhaps, not surprising to the public, since they had been featured as necessary in all the science fiction of the Twentieth Century, beginning with early works like H. G Wells’s “The First Men in the Moon”, Garrett P. Serviss’s “Edison’s Conquest of Mars”, and later films like George Pal’s classic “Destination Moon”. The need for spacesuits is obvious, because space is a vacuum.

But think about this for a moment with me. This was in a time before any human, before any human machine, had ever been to “outer space.” Based on your everyday experiences, you could reasonably expect the environment of space to be exactly the same as here on the surface of the planet — why wouldn’t it be filled with air and wind?

That seems weird to say out loud, but it shows how good our society is at assimilating scientific fact — objective truth — and incorporating it into our understanding of the world. But it begs a lovely question: having never been to space, how did we figure out it was empty and devoid of air? How could we possibly know what to expect and how to prepare for our voyages there? The human species has developed a remarkable ability to observe the world around us, to discern the few simple rules that govern how it behaves and evolves, and use that knowledge to move into the future.

The story begins not with a contemplation of space, but with a contemplation of Earth, and in particular its atmosphere. We are used to characterizing the world around us because it is made of things we can touch, pick up, and see — rocks, leaves, hunks of metal, water, snow, jack rabbits, and so on. But what about things we can’t see? Glass, for instance, is transparent, but not completely so — you can usually tell if there is a pane of it in front of your face, and if you break it you can certainly see its edges and pick up pieces.

Glass is nearly invisible — you can see right through it. But it is substantial enough that you can see edges, can see that it is there. You can pick it up, do experiments on it, and figure out what it is all about. Note also: there is air in this picture, but you can’t tell! [Image: S. Larson]

The air, however, is a trickier thing to talk about. You and I, we’ve grown up from a very young age being told that the air exists, and what it is, and what it is made of, and how it behaves. Looking back through the ages, there was a time when none of that was known, when no one had ever seriously contemplated the question “what is the air and what is it made of?”

Humans are a curious lot, and we all begin our lives as explorers and investigators. Most children discover early on that air exists while playing in the water.  If you take a glass and turn it upside down before submerging it in a tub of water you make a curious discovery — water does not rush into the glass and fill it up. Why not? There must be something in the way! What is it? It is air. Of course it is.

(L) A common game is to trap air in an upside down glass or cup. If you look closely here, the upper line is the interface between the water and the outside of the glass; the lower line is the interface between the trapped air and the water, under the surface of the water! The water cannot go into the glass because the air is in the way. (R) This is the opposite experiment: if you put water in the cup, invert it, and lift up, you can pull water up above the surface! [Images: S. Larson]

It is a simple observation, it is a simple conclusion, but the implication is profound — you can investigate and discover something that is invisible, something you can’t control, something you can’t hold in your hands. You can do the experiment over and over and over again, and you’ll get the same result. You can use a different cup, and a different pond or lake or sink, and you’ll get the same result. You can send a letter to your friend who lives on the other side of the world and describe what you have done, and they’ll get the same result. This is the fundamental basis for how we think about the world around us — we make observations, we consider them and expand them to the best of our ability, and we figure out how the world works. Our musings culminate in a set of rules that we call “the Laws of Nature,” and we all agree that these rules govern experiments everywhere. We use those rules to try and understand how the rest of the world works. We use those rules to harness our interface with Nature, and improve the human condition. This practice of discovering the Laws of Nature and using them has a name — “SCIENCE.”

The simple child’s game described above allowed us to “discover” something invisible — the air. What else can we find out about this “air” stuff? Just knowing that something exists can get you far, but not very far. At some point you need to know more. Other objects you encounter have measurable properties. A rock or a bag of Skittles has a size, has a color, behaves a certain way when you squeeze it, and has a weight. So one might ask all those same questions about the air.  So what do you think? Does air weigh anything?

At first glance, it seems a silly question because you don’t notice it weighs much. Never-the-less, it is a legitimate question, and one that is worthy of investigation. The first record of an experiment to measure the weight of air is in a letter Galileo wrote to Giovanni Battista Baliani in 1613 describing an ingenious method that you can utilize at home.

Make a simple balance by hanging a stick around its center by a string. On each end of the stick, hang an aluminum can so that the entire apparatus is balanced. If your significant other complains about this, either (a) convince them it is a piece of art, or (b) tell them you are recreating a frontier science experiment from the 1600s.

If you heat a can up, air is expelled from the can. Placing a candle under one can and heating it up will cause that end of the balanced experiment to rise. Why? Because it got lighter — the expelled air had mass of its own. By pushing air out of the can, the combined weight of the can and air decreased, and the balance became unequally weighted — the heavy side (with air) tipped down.

A home hacked version of the experiment Galileo described to Baliani in 1613. (Top) Two “empty” containers [they have air in them] are balanced on a beam. (Bottom) When one of the containers is heated, air is expulsed and the total weight decreases, causing that end to rise. [Images: S. Larson]

You will often see versions of this experiment described with balloons instead of cans; the weight of air can be understood in this way, but the physics is more subtle. Using a rigid container makes it more straight-forward. If you want to prove to yourself that air is expelled from a heated container, take a bottle on its own and put a balloon over the neck. When you heat the bottle, the balloon will inflate as a result of air being pushed out.

Evangelista Torricelli [Wikimedia Commons]

The discovery that air had weight was the beginning of serious examinations of the atmosphere. One of the earliest important innovations came from Evangelista Torricelli, who worked with Galileo in 1641, for the last three months before Galileo died. In 1643, he invented the first mercury barometer, showing that air had pressure.  When air pressure is high compared to when the barometer is set up, the barometer rises; when air pressure is low compared to when the barometer is set up, the barometer sinks.

The figure below shows how Torricelli’s barometer works. Begin with an empty glass test tube, filled with air. Fill the tube up completely with mercury, and cap it (pictures of Torricelli doing this often show him holding his thumb over the end, the way you might do on a garden hose!). Invert the test tube in a small bowl of mercury, and remove your thumb with the top of the tube beneath the surface. The level of mercury in the tube will fall causing the level in the bowl to rise, but will eventually stop.

Basics of a Torricelli Barometer. (A) Start with a tube filled with air. (B) Fill the tube completely with mercury. (C) Invert the tube in a bowl of mercury. (D) The mercury settles out and leaves a vacuum behind; air pressure pushes on the bowl holding the remaining mercury in the tube. [Image: S. Larson]

Why does it stop? The pressure of the air (green arrows) is strong enough to keep mercury inside the tube!  What is left behind in the tube when the mercury level sinks? Absolutely nothing. This is called a Torricellian vacuum, and was the first time a vacuum had been made in the laboratory. In fact, it was the first time that a vacuum had ever been demonstrated to even exist, pointing the way to the possibility that vacuums exist in Nature.

There are a variety of neat ways you can build your own barometer at home to see changes in pressure, using Torricelli’s method, straws and glassware, and water.  However my favorite barometer is simply a sealed bag of chips. Food products like chips are sealed at the factory, and have a certain amount of air trapped inside the bag with them. If the external pressure of the air changes, then the air inside the bag either can’t resist being pushed inward (crushing the bag when air pressure is high), or it can’t resist pushing outward (blowing the bag up like a balloon when the air pressure is low).

Torricelli could have also made his discovery on a road trip with a bag of potato chips. Here’s a bag I drove up I-80 to the Sherman Summit, 8640 feet above sea level, in Wyoming. [Images: S. Larson]

Torricelli’s invention was quietly explained to colleagues and other scientists in Europe at that time. In 1647 it was brought to the attention of Blaise Pascal, who deduced it must be the weight of the air pressing down on the bowl of mercury, preventing the weight of the mercury in the tube from falling further. If the air had some measurable and finite weight, then it must not stretch infinitely far above our heads, Pascal reasoned. There must be a top to the atmosphere. And if there was a top to the atmosphere, the weight of the air above you must decrease as you go higher — say climbing a tower, or walking up a tall hill or mountain. In 1648, Pascal convinced his brother-in-law to carry a barometer up the 1460 meters up the slopes of Puy-de-Dôme in France, and showed that it was so.

For the next three centuries, experiments with vacuum in laboratories continued. The Earth’s atmosphere was measured and tested on the highest mountains we could scale. We could understand the trends and behaviour of the ocean of air in which we swim, and thus predict what we would encounter when we crossed into space. In all that time, we never reached space itself, but we knew what we would eventually find there. On 4 October 1957, Sputnik rose on a tongue of flame, borne aloft by a rocket based on a missile into an orbit that ranged from 215 to almost 940 kilometers above the Earth. An orbit, which as expected, was beyond the rarified edges of what you and I regard as the atmosphere, truly in the vacuum of space. It was as we had expected from long contemplation and experiment here on Earth — the laws of Nature are immutable, and they apply everywhere in the Cosmos, even hundreds of kilometers above our head.

This is the nature of science. It is not a philosophy, it is a method of exploration, a method of understanding the Cosmos of which we are a part and using that understanding to improve our lives. It is not perfect, but it is self-correcting and extensible, able to assimilate new data and information to update our knowledge of the Universe, as we did when we discovered the existence of the vacuum. It is deadly accurate when it makes predictions based on overwhelming evidence. It is, so far as we know, the best method for discovering new knowledge and solving problems.

Songs from the Stellar Graveyard (GW170817)

by Shane L. Larson

Bernie Capax meets Death in Brief Lives, by Neil Gaiman.

In Neil Gaiman’s transcendent literary comics series The Sandman,  the Endless are echoes of the patterns of force and existence that define the Universe. Among them is Death, who at the end of our lives, collects us and escorts us from this Universe. As she says to Bernie Capax, who had walked the world for some 15,000 years, “You lived what anybody gets… you got a lifetime.”  (issue 43, contained in the collection “Brief Lives“).

If there is any truth in astronomy that we have learned over the last few centuries, it is that the Universe itself evolves. The stars are born, they live their long lives, and ultimately they perish and decay away. Death waits for them too. The galaxy is littered with the remains of stars that once were. From our vantage point here on Earth, we peer out into the Cosmos and glean what we can with the meager view we have in our telescopes. We have mapped billions of stars, and millions of galaxies. But in the stellar graveyard, we have only seen a handful of objects — we know precious little about the skeletons of the stars, because they simply don’t emit much light.

On 17 August 2017, at 7:41:04 am CDT, a faint whisper from the stellar graveyard washed across the shores of Earth. It showed up first in the LIGO-Virgo gravitational wave network, which was deep in our second observing run (what we call “O2”). At that particular moment, we were all wound up and celebrating because just three days before, we had made our first joint detection with LIGO and Virgo together (a pair of black holes called GW170814). When signals register in our network, the automated software (we call them “pipelines“) generates initial numbers about what the source might be, and that morning we knew we had something special. Our group lead at Northwestern was spinning us all up to start doing computer simulations, and in an early email to us she said what we all knew: this is life changing.

On the first day, we were sending emails that had the inkling already of how important this discovery was.

Why? Because the mass of the objects in the new signal were smaller than anything we had seen in gravitational waves before — all together less than about 3 times the mass of the Sun. Our predisposition from all our years of experience in astronomy said that could mean only one thing: the LIGO-Virgo network had just detected the first binary neutron star merger in history. Today, we call this event GW170817.

Spectrograms show how the frequency of the signal (vertical axis) changes in time (horizontal axis) in each of the three detectors. The long swoop up and to the right is called a chirp. [Image: LIGO-Virgo]

But the story gets better. 1.7 seconds after the gravitational wave signature, the Fermi Gamma-ray Burst Monitor (GBM), in orbit high over the Earth, registered an event — a short gamma-ray burst, now called GRB170817A. This was hugely significant, because we have often speculated about what causes gamma-ray bursts. For short gamma-ray bursts we’ve long thought it must be colliding neutron stars.

The discovery of GRB170817A by Fermi-GBM. [Image: NASA/Fermi]

What are these neutron stars? They are the dead skeletons of stars, one possible outcome of a colossal stellar explosion known as a supernova. They are extreme objects. They have about one and a half times the mass of the Sun packed inside a sphere about 20 kilometers across (about the size of a city). That means they are extraordinarily dense — a tablespoon of neutron star matter would weigh 10 billion tonnesabout 30 times the mass of all the humans on planet Earth. Gravity on the surface is outrageously strong — about 190 billion times the strength of gravity on the surface of the Earth; if you had the misfortune of falling off a 1 millimeter high cliff, you would be travelling almost 220,000 kilometers per hour when you hit bottom (136,000 mph).

A neutron star (diameter 20 km) scaled to the Chicago skyline. [Image: LIGO-Virgo/Daniel Schwen/Northwestern]

One thing we know about the lives of the stars is that many of them live together with a partner, orbiting one another in a fashion similar to the Earth orbiting the Sun. Like human life partners, one star inevitably reaches the end of its life first, and expires in a supernova. Some such stars become neutron stars. Eventually, the second star in the pair also dies, and if it supernovas, then one end state is two neutron stars, left in an orbital dance with the skeleton of their partner. One might think that is the end of the story for such stars, but there is still one final chapter in this tale from the stellar graveyard. The orbit of the two neutron stars can and will shrink over time through emission of gravitational waves. Of course, we’ve detected gravitational waves before (GW150914, GW151226, GW170104, GW170814), but this time it’s different. Why? We’re talking about neutron stars instead of black holes, which means there can be light, and indeed there was.

The collision of the neutron stars smashes all the matter together, and under such energetic circumstances, matter generates light. The gamma-ray burst was only the beginning. The collision sheds matter into a volume around the merging pair. This matter, suddenly free of the strong nuclear forces involved in the dense matter of the neutron star, recombines and makes heavy elements (physicists call this “r-process nucleosynthesis“). This recombination also creates light, and is called a kilonova. Following the gamma-ray burst there is also a long term afterglow, from the energetic jet of the gamma-ray burst blasting through the surrounding interstellar medium.

Different phases of emission of electromagnetic radiation from the binary neutron star merger. (L) The initial gamma ray burst. (C) The kilonova from nucleosynthesis. (R) Long term afterglow from energized material around the event. [Images: NASA-GSFC SVS]

The LIGO error ellipses plotted on a skymap of the Hydra-Virgo region. The galaxy NGC 4993 is visible in amateur telescopes. [Image: S. Larson]

Together, the LIGO and Virgo detectors can determine where on the sky a source comes from, though not perfectly. They can point to a region called the gravitational-wave error ellipse. For Gw170817, the ellipse on the sky was narrowed down to just about 30 square degrees — an area about the size and shape of a small banana held out at arms length. The error ellipse spans the boundary between the constellations Hydra and Virgo, with a little tail that stretches into Corvus. This was a difficult position in the sky because at the time of the discovery in mid-August, it sets very shortly after sunset. Never-the-less, telescopes around the world began an intensive imaging search, and just 10.9 hours after the detection of GW170817 and GRB170817A, an optical signal was discovered by the Swope telescope in Chile — a pinpoint of light on the outer fringes of the galaxy NGC 4993 that was not there before. Over the course of the next 10 days, the kilonova faded away; in the end more than 70 observatories worldwide imaged and measured the kilonova.  It has been a historic discovery and observing campaign. This is the beginning of multi-messenger astronomy with gravitational waves.

An image of the kilonova associated with GW170817; the fuzzy blog is NGC 4993. [Image: TOROS Collaboration, M. Diaz]

So what can you do with gravity and light together? As it turns out, an awesome amount of science! Today there is a virtual raft of papers being published (the first wave of many, I expect) outlining what we have learned so far. There are too many to explain them all here, but let me just outline a few that stand out to me.

Probably the most important outcome is the confirmation of the connection between short gamma-ray bursts and binary neutron star mergers. Gamma-ray bursts have been a mystery for more than 40 years. First discovered in the 1960s by the military using satellites meant to monitor nuclear weapon tests, the discovery that they were of cosmic origin was revealed to the scientific community in the 1970s. Since then many ideas and models to explain their origin and intense energy have been explored, but none have been confirmed because the engines — the astrophysical systems that drive them — are far too tiny to resolve in telescopes. The LIGO-Virgo detection of gravitational waves confirms that neutron star binaries are the progenitor of short gamma-ray bursts.

The result that I’m most excited about is we used GW170817 to measure the expansion of the Universe. The expansion of the Universe was first noted by Hubble in 1929, by measuring the distances to other galaxies. This was being done just 5 years after the discovery that there were other galaxies! Fast forward 88 years to 2017 — we’ve measured the expansion of the Universe independently using the distance to a galaxy with gravitational waves and light from telescopic observations together. This measurement comes just two years after the discovery of gravitational waves!  It gives me no small amount of pleasure to echo that historic discovery so close to the beginning of this new era of astronomy. 🙂

Top shows Hubble’s original 1929 diagram (from PNAS, 168, 73[1929]); bottom shows the location on this diagram of the GW170817 measurements, at the + mark. [Image: W. Farr/LIGO-Virgo]

We try and write public accessible versions of our papers in the LIGO-Virgo Collaboration. If you’d like to explore some of the science we’ve been doing, try out some of our science summaries.

There are of course many things we still don’t know about the discovery. Foremost among them is this: what is the thing that formed after the merger of the two neutron stars? Some of us in the astrophysics community think it might be some kind of exotic super-neutron-star, larger than any neutron star ever detected. Some of us in the astrophysics community think it  might be some kind of exotic light-black-hole, smaller than any black hole ever detected. Whatever it is, it lies within a very fuzzy range of masses that we call the mass gap — a range of masses where we have never seen any stellar remnant. What is the lightest black hole Nature can create in the Universe?  What is the heaviest neutron star Nature allows? These are questions we would very much like to know the answer to. At least for the moment, it seems we may not learn the answer from GW170817, but with future detections of binary neutron star mergers we may.

The masses of known stellar remnants discovered by both electromagnetic and gravitational wave observations. Between the black holes and the neutron stars is the “mass gap.” [Image: LIGO-Virgo/Frank Elavsky/Northwestern]

So here we are. We are all simultaneously exhilarated, relieved, joyous, and eager for more discoveries to be made. We’re very tired from late nights analyzing data, arguing about results, writing papers, and furiously preparing ways to tell our story to the world.

We could all use a nap. And a pizza.

Because this is only the beginning, the culmination of decades of hard work, difficult hardships, and anticipation. And the best is yet to come. I’m so happy that I’ve seen these days. Being tired doesn’t bother me, all the struggles getting to this point don’t bother me either, because I got to watch it unfold. As Death said, we get what anyone gets; we get a lifetime. These are the moments, the discoveries, that are filling that lifetime up.  Onward to the next one.

———————-

This post is the latest in a long series that I’ve written about all the LIGO detections up to now.  You can read those previous posts here:

The Harmonies of Spacetime – GW150914

My Brain is Melting – GW150914 (part 2)

The Cosmic Classroom on Boxing Day (GW151226)

New Astronomy at the New Year (GW170104)

Focusing our Gravitational Wave Attention (GW170814)

———————-

I have many LIGO and Virgo colleagues who also blog about these kinds of things. You may enjoy some of their posts too!

 

Focusing Our Gravitational Attention (GW170814)

by Shane L. Larson

Nature guards her secrets jealously, and wresting them from her grasp is an arduous, and frustrating task. One of the great difficulties of the modern world is that knowledge is so easy to pull up, with the flick of a finger across a screen, that we forget how hard it was to obtain that knowledge in the first place. Every bit of knowledge that you and I take for granted was earned, at great cost, by a long line of humans who came before us.

Knowledge is hard to come by, a fact that we often forget in an age where virtually any and all information is readily available on demand with a handheld device. [Image: S. Larson]

For just more than two  years now, we have lived in a new astronomical era, where astronomers have the ability to sense minute deviations in the shape of spacetime and use them to discover the secrets of the Cosmos. We call this science gravitational wave astronomy.

This new branch of observational astronomy burst on the scene with much fanfare in early 2016 when it was announced that the two LIGO gravitational wave observatories had detected a pair of black holes merging far across the Cosmos. We knew roughly where it was in the sky, but only roughly in the same sense that “Kansas is roughly in North America.” The physics of how an instrument like LIGO works means detection is easier than pointingpointing to a gravitational wave source on the sky is hard, because Nature guards her secrets jealously.

We call gravitational wave detectors “observatories“, but they are very different from traditional telescopic facilities that you and I are familiar with. Telescopes work more or less like your eyes — they point in a given direction, and are sensitive to a narrow space in front of them (what astronomers call the “field of view“).

A daytime picture of the Moon, taken by holding my phone up to the eyepiece of my backyard telescope. The field of view is not much bigger than the Moon, which is very small on the sky. [Image: Shane L. Larson]

By contrast, gravitational wave detectors are largely omnidirectional — they can sense gravitational waves from every direction on the sky, though some directions are easier than others.  They are much more like your ears in this way. If you close your eyes, you can hear sounds in front of you, above you, to the sides, or behind you. You can usually point at a source of a sound, but that is because your brain is using both of your ears together to triangulate the position of the source of sound. Here’s an experiment: close your eyes and plug one of your ears. Have one of your friends stand somewhere in the room and sing “The Gambler” (here’s a version I particularly like, by First Aid Kit) and see if you can point to them. It’s not so easy to point with only one ear.

We use this same method of triangulation in gravitational wave astronomy — multiple detectors can point better than single detectors alone. The more detectors, the better a source of gravitational waves can be found on the sky.

The Virgo gravitational wave observatory, outside of Pisa, Italy, looking roughly northward toward the Monte Pisano Hills. [Image: Virgo Collaboration]

For the past two decades, at the same time LIGO was being built, our colleagues in Europe were constructing another gravitational wave observatory outside of Pisa, called Virgo. On 1 August 2017, the Advanced Virgo detector joined the two Advanced LIGO detectors in the search for gravitational waves.

There was much celebration in the LIGO-Virgo Collaboration that day, because gravitational wave detectors are not easy to build. Getting to the moment where all three advanced detectors were online together was a tremendous accomplishment, and one that held much promise. With three detectors, we should be able to pinpoint gravitational wave sources on the sky better than ever before. The holy grail of events would be to make a detection, and narrow the skyview to an area so small that one could reasonably point a telescope there and possibly see a simultaneous signal in light.

Doing directed astronomy with gravitational wave detectors requires a network of many facilities. As time goes on, more are being built around the world.

We held our breath, and dared not hope. That’s the nature of astronomy — it’s a spectator sport. All we can do is turn on our instruments, and sit here on Earth and wait for the Universe to do something awesome.

As it turns out, we didn’t have to wait long for something awesome. On 14 August 2017, all three detectors registered the gravitational wave signature from a pair of merging black holes.  At about 5:30am CDT in the United States (10:30:43 UTC), a signal came sailing through the Earth, ringing off each of the three gravitational wave detectors that were diligently collecting data, hour after hour, minute after minute, waiting for the Cosmos to do something. Nature did not let us down. The signal was a strong series of spacetime ripples, with the same pattern, showing up in each of the three detectors. We call the event GW170814 (here is a LIGO-Virgo factsheet on the event), and it brings the total number of events in the gravitational wave catalog to 4.

The GW170814 signal, as gravitational wave astronomers like to represent it. The top row shows the spectrograms, showing how the frequency (analogous to the pitch of a sound) evolves in time, chirping as you go from left to right. The lower row shows the waveform traces in time from left to right, growing stronger as the black holes approach and merge, then tapering away. [Image: LIGO-Virgo Collaboration, from our paper]

Below, I show a table I keep of events, and it is getting harder to manage! I like to take it out and stare at it sometimes because you can see a story beginning to emerge, and for a scientist there is nothing more exciting. A story is exactly what we’ve been trying to learn from Nature, but you can seldom figure it out from just one astronomical event. It is only the long, slow accumulation of happenings in the Cosmos that lets us begin to see the tantalizing patterns of what is going on. Lots of black holes. We’re beginning to get a sense for some trends in their masses. We’re beginning to figure out how many there might be, and how common they are in the Universe. Scientists, as a general rule, are a cautious lot. It will still be a while before there are definitive statements on Wikipedia or in astronomy textbooks. But buy your favorite gravitational wave astronomer a bag of jelly donuts (I also like Dr. Pepper), and they’ll talk your ear off about what we’re beginning to figure out.

My updated gravitational wave catalogue. [Image by Shane L. Larson]

But the real story of GW170814, is Virgo. Virgo came roaring on the scene, and transformed our ability to point on the sky. The sky location graphic below shows all of the gravitational wave events seen to date (including one interesting signal, called LVT151012 that wasn’t quite strong enough for us to make out perfectly in the data, but looks an awful lot like a black hole pair).  In every previous detection, the source was known to lie in some great banana shaped region of the sky that we call an error ellipse. With the addition of Virgo to the network, and the arrival of GW170814, we see the dramatic and awesome difference it makes, collapsing the giant banana of an error ellipse into a much smaller bubble on the sky. This bubble lies near the southern end of the constellation Eridanus (if you’d like to look at a starmap, it came from an area around RA = 3h 11m, DEC = -44d 47m). At the moment of the event, the source was directly overhead southern Chile.

The sky location of all gravitational wave events to date. [Image: LIGO/Virgo/NASA/Leo Singer (Milky Way image: Axel Mellinger)]

There were no detected signals with light associated with the event, but these were after all, black holes. By definition, black holes emit no light; if there is going to be something for traditional telescopes to see, there is going to have to be some kind of matter involved. And so, we wait for the next one. We can tell we’re on the cusp of a tremendous new era of astronomy. We still haven’t found the holy grail, an event seen with both gravitational waves and light, but we continue to look. With our growing network of detectors, and scientists around the globe, we will eventually make that discovery too.

Until then, my heartfelt congratulations to my colleagues and friends who I work with on LIGO and Virgo — here’s to many more long years of searching the Cosmos. Viva Virgo!

——————

You can read about the previous LIGO detections in my previous posts here:

The Harmonies of Spacetime – GW150914

My Brain is Melting – GW150914 (part 2)

The Cosmic Classroom on Boxing Day (GW151226)

New Astronomy at the New Year (GW170104)