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.

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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.

The Cosmos in a Heartbeat 2: Coming of Age

by Shane L. Larson

Astronomy from your backyard is dominated by naked eye stargazing, and optical telescopes that gather exactly the same kind of light you see with your eyes. There are a few amateurs who ply the skies with radio telescopes, or build cosmic ray detectors in their kitchens, but for the most part it is traditional telescopes. When I first started my studies in astophysics, this was still largely true of professional astronomy, though there were a few advanced experiments that were building the technology needed to survey the Cosmos using astroparticles, and a robust effort to design what would become the world’s first successful gravitational wave detectors.

One of the things that is true of all telescopes, no matter how they are designed to see the Cosmos, you can always build a better instrument that can observe more. In the context of astronomy, “more” means detecting cosmic phenomena that are difficult to perceive, or probing deeper into the distant Universe.

My two current telescopes (both homebuilt). The one on the left is called Equinox (12.5″ f/4.8 Dobsonian Reflector) and the one on the right is called Cosmos Mariner (22″ f/5 Dobsonian Reflector).

For optical telescopes, bigger is better. The larger the mirror, the easier it is for the telescope to capture a few tiny bundles of precious light that arrive on Earth and gather them all together in one place (your eye, or a camera) so there are enough to be bright enough to see. When I first started in backyard astronomy, I had an 8-inch telescope, which is about 30 times larger than the pupil of my eye, and so can gather almost 850 times more light than my eye. That first telescope of mine has been passed down to my daughter as part of her growing interest in backyard astronomy. It has changed its look, but its heart is still the telescope that I spent many hundreds of hours out under the night sky with. I’ve built a new, bigger telescope to replace my old one. Shown above is my telescope called Cosmos Mariner, and has a 22-inch mirror in it. That mirror is about 80 times larger than my pupil, and can gather more than 6000 times the light my eye can!  Mariner can probe deep into the Cosmos, and I use it as often as I can to soak in the wonder of the night sky.

The Hubble Space Telescope. Arguably the most capable and successful telescope ever built by humankind. [Image: NASA]

Professional astronomers have also been building bigger and better telescopes. Shown above is the Hubble Space Telescope, which launched in 1990, and is arguably the most successful scientific instrument in history. It’s mirror is 2.4 meters in diameter, but it peers at the Universe from a vantage point high above the atmosphere of Earth. In its three decades of observing, it has seen farther and seen more than any telescope in history. All told, some 10 to 15 thousand papers have been written about what Hubble has seen in the Cosmos. When we build a machine like Hubble, we always have grand plans for it. One of the tasks we had in mind was to use Hubble’s size and vantage point high above the Earth to take a picture of the Cosmos unlike any other before it. We picked a non-descript region of the sky in the constellation Eridanus, and over the course of a decade, asked Hubble to go back and look at that point over and over and over again, until it had stared at that one spot for a total of 23 days. You take all those individual pictures, and you stack them together to make a single new picture.

The Hubble Extreme Deep Field (XDF). [Image: NASA/ESA]

What you find is that in a region of the sky where you thought there was nothing, there is very definitely something. We call this picture the Hubble Extreme Deep Field. This image covers an area on the sky roughly the size of the eye of needle, held at arms length. Within it, virtually every fleck of light and color you see, is another galaxy. All told there are some 5000 individual galaxies in this image, implying that across the entire sky there are several hundred billion galaxies. This is what we mean when we say the Cosmos is vast beyond our wildest imaginations.

The Hubble Extreme Deep Field is a flat, two-dimensional image not unlike other pictures you are used to looking at. But one of the things we can do in modern astronomy is measure the distances to galaxies, so we can make a movie of what it would be like if you could dive into this image, making the impossible journey from Earth to the most distant galaxy in the image. If we launch ourself on that voyage, the first thing we notice is that over most of the journey, we are travelling through nothing at all.

The Universe, on the grandest scales, is mostly empty of any ordinary matter like you and me or stars or galaxies.  As we plunge deeper, we do encounter groups of galaxies — they tend to cluster and grow together, making a vast cosmic web that fills the entire Cosmos. Many of the galaxies we pass look familiar, like we expect galaxies to look. But as we travel farther and farther into the Deep Field, we are looking back farther and farther in time, until we reach the most distant galaxies in the image. These are the youngest galaxies we’ve ever seen, born barely 450 million years after the birth of the Universe. Astronomy is a special kind of time machine — looking back across the Cosmos is looking back in time. We can see how galaxies were long ago, in an effort to understand how our own galaxy might have been long ago as well.

The surface facilities of IceCube at South Pole. [Image: IceCube Collaboration]

Our colleagues in neutrino astronomy have been building their own new generation of observatories as well. Today, the pre-eminent neutrino observatory in the world is located at South Pole Station, and is called IceCube. IceCube is a series of 86 deep cores drilled 1.4 to 2.4 kilometers down into the Antarctic ice. Long strings with camera modules are lowered into the bores on cables, and the ice refreezes around them; all told there are more than 5000 cameras (“Digital Optical Modules”) in the array.  Observing with IceCube is in principle the same as KamiokaNDE — neutrinos pass through the Antarctic ice, and sometimes interact with the atoms of the ice to produce a burst of light that is picked up by the cameras on the strings. 

The IceCube array is encased in the ice underneath the surface station. [L] The long ice cores contain strings with cameras, and when an event passes through the array the light is detected by some of them. [R] The most energetic neutrino event yet detected, on 22 September 2017. [Images: IceCube Collaboration]

In September 2017, IceCube picked up the most energetic neutrino ever observed. It blasted through the array at  20:54:30 UTC (around 2:54pm Central Standard Time), and was detected by a long sequence of camera modules that stretched from one side of the array to the other. Looking at the shape of the data in the array, and in particular which side of the array lit up first in the detection, allowed astronomers to point backward from IceCube to the point on the sky where the neutrino came from.

An artists impression of a blazar, a type of active galactic nucleus with a supermassive black hole at the center, and an energetic jet pointing at the observer (us, on Earth). This is the type of object the IceCube neutrino event was traced back to. [Image: DESY Collaboration]

Using this pointing information, astronomers searched that region of the sky and discovered a blazar called TXS 0506+056. A blazar is a kind of galaxy that has an active galactic nucleus (AGN). AGN are supermassive black holes that have a swirling maelstrom of gas and material around them that slowly feed the black hole. When gas gets close to the black hole, the gravitational attraction propels it onto high speed orbits around the black hole. All of the gas swirling around together interacts strongly with the rest of the gas and as a result gets very hot; hot gas glows brightly, especially in ultra-violet and x-rays, both very energetic forms of light. The bright light can be seen in telescopes from Earth indicating the presence of a supermassive black hole. As the gas swirls ever inward, some of it eventually falls into the black hole, vanishing forever. Some of it, however, is spining so fast it cannot fall onto the black hole, and gets squirted out into an energetic jet, propelled away from the nucleus of the galaxy at enormous speeds. This is characteristic of AGN; a blazar is simply an AGN where the view from Earth is staring directly down the jet.

All the material being ejected down the jet is moving at very high speeds, and still collides with other material making its own way out through the jet. This energetic environment is not unlike our own particle accelerators here on Earth, and at some point along the jet a collision between particles created the neutrino we detected with IceCube.

This is once again multi-messenger astronomy — observing the same astrophysical object, using both astro-particles and telescopes. What is different in this case is the discovery was led by neutrino astronomers, who guided telescopes toward the right place in the sky.

The twin 10-meter Keck Telescopes on Mauna Kea. [Image: Wikimedia Commons]

Now, most of us know what astronomers know: black holes are AWESOME. Active Galactic Nuclei are not the only big black holes in the Cosmos. There is, in fact, a massive black hole much closer to home, in the center of our own Milky Way. Astronomers on the ground have been building bigger and bigger telescopes, and today among the largest telescopes in the world are the twin 10-meter Keck Telescopes on Mauna Kea, in Hawaii. We’ve been using the Keck Telescopes, togther with others around the world, to peer at the exact center of the Milky Way for the past two and a half decades. The telescopes have been able to detect a small cluster of stars we call the “S-Cluster.” We’ve been watching them long enough now that we have not only seen the stars move on their orbits, but we’ve seen some of them complete their orbits.

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]

If you remember back to your early classes in physics or astronomy, you may remember that someone like me once told you that if we can measure orbits, the Universal Law of Gravitation (published by Newton in 1687) can be used to discover the size of the mass that is driving the orbit. For the S-Cluster of stars, the size and timing of the orbits says there is a 4 million solar mass black hole at the center of the galaxy. How do we know it is a black hole? It is emitting no light, and it is so small it competely fits inside the orbits of the stars!

Among this cluster is a star we call SO-2. It is the star closest to the black hole. Every 16 years, its highly elongated orbit dips down to its closest point (what astronomers call the “periapsis”), and zips around the black hole in a quick slingshot. In just the course of a few months, this 15 solar mass star completely changes the direction it is moving through space. THAT is the power of a massive black hole! In May 2018, we watched SO-2 make the second periapsis pass we’ve seen since observations began (the last was in 2002), giving us the most precise measurements to date of the properties of the black hole. By all accounts, the black hole at the center of the Milky Way has all the properties and behaviours predicted by general relativity.

This story serves to introduce us to one of the emerging wonders of modern astronomy — that we are beginning to understand that we can use gravity itself to probe the Cosmos. In the case of SO-2 we are using the influence of gravity to tell us something about the black hole, an object which by definition emits no light. But a century ago, when general relativity was newly minted and first being pondered by Einstein, he had another notion: perhaps we could observe gravity itself — don’t use telescopes at all, but instead build a machine of some sort that plumbs the Universe with some other sense, a sense that we humans do not posses at all.

This illustrates the basic premise of gravitational wave detection using laser interferometers. [TOP] Imagine a ring of small masses. If a gravitational wave is coming straight out of the screen at you, it distorts and warps the ring, first making it long and skinny, then a bit later making it short and wide, and then back again. [BOTTOM] The idea of detection with an instrument like LIGO or LISA is to use mirrors for three of the masses on the rings. As the distance is warped between the masses, the time it takes a laser to travel between them changes. [Images: Shane L. Larson]

Einstein’s idea was simple. What you and I call “gravity” fills space and can change with time, and so the information about how it is changing must be able to be transmitted from one place in the Cosmos to another at the speed of light or less. That propagating message is what we today call a “gravitational wave.”  It is one thing to deduce that such gravitational signals must exist, and quite another to decide what that means and how to build an instrument to detect them. It took until 1957 for physicists to even come to agreement on what gravitational waves do to the world around us. After much arguing and debating and confusion and aggravation, it was realized that they warp spacetime — they change the proper distance between any two masses in a repeating pattern of stretching the distance out and compressing the distance down.

The effect is extremely tiny, so tiny as to be unnoticeable in everyday life, and so tiny as to be discouragingly small if you want to build an experiment to look for the effect. But physicists are a diligent and resilient bunch, and a few of them began to think about exactly how to build such an experiment. Fast forward to today, and six decades of thinking have culminated in one of the most exquisite astronomical observatories ever built: the Laser Interferometer Gravitational-wave Observatory — LIGO. In 2015, LIGO was the first gravitational-wave observatory that was able to successfully detect gravitational-waves, in that case from two merging stellar-mass black holes. Many more discoveries followed, all of them of black holes, until August of 2017.

Left to Right: LIGO-Hanford (Hanford, Washington), LIGO-Livingston (Livingston, Louisiana), and Virgo (Pisa, Italy).

In late August, people across North America were gearing up for a total solar eclipse that was going to race across the continent from Oregon to South Carolina on August 21. But just four days before, in the early morning hours in North America (7:41am Central Daylight Time), the Universe blasted us with gravitational waves. This particular event was unlike any previous gravitational wave event we had seen. It was accompanied by an almost simultaneous burst of gamma rays, detected by NASA’s Fermi Gamma Ray Telescope, in orbit high above the Earth. The two LIGO facilities, together with our European colleagues using their Virgo detector outside of Pisa, measured the masses of the event telling us we had just observed the merger of two neutron stars — a kind of dead stellar skeleton that can be left over when stars explode at the end of their lives. LIGO and Virgo were able to pinpoint the location of the event to a small region on the sky. By the end of the day, as the Sun set on professional telescopes around the world, the search was on and the fading light of the event was discovered in a small galaxy known by the name NGC 4993. The light gathered by observatories around the world over the next many months (and continues today) showed that this event was an explosive phenomena known as a kilonova. In less than 24 hours, this single event transformed modern astronomy — literally, in the blink of an eye.

The initial detection resolved a great mystery that had confounded astronomers since the 1970s — short gamma ray bursts (like the one detected by Fermi) were the signature of merging neutron stars (detected in gravitational waves). The continuing observations of the kilonova resolved another great mystery — kilonova are the expanding, cooling shattered remains of merging neutron stars. From that cooling and expanding morass of nuclear material that was once the neutron stars, the stuff of us is made in large quantities — the heavy elements on the periodic table, built from the death of dead stars!  All of these ideas are ones that astronomers have speculated about, imagined, and calculated for many years up to now, but the observation, the multi-messenger detection of gravitational waves and light has, for the first time, shown us that some of our thinking is along the right tracks.

It is remarkable to witness this evolution in our thinking about the Cosmos. When I started in astronomy (both in my backyard and in my professional endeavours), our thinking was dominated by telescopes because those were the instruments we had and the tools we had been successful at building and using. We were just starting to try to expand our toolbox, to develop a new repertoire of machines to unravel the story of the Universe and our place within in. Now, at the middle of my life and career, those idle daydreams, those grand ponderings of what might be possible, have come to fruition. 

Now we turn our eyes to the future, and ask “what next?”

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This post is the second 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 (this post)

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

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.

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

by Shane L. Larson

The night sky over the Pando Forest in central Utah. Pando is an 80,000 year old aspen grove — it has seen almost 30 million nights like this one, far more than any single human will ever live through. [Image: Shane L. Larson]

The Cosmos is vast in ways that are difficult for humans to wrap their brains around. That doesn’t stop us from talking about it, of course, but it is vast, none-the-less. What do I mean by “vast?”

The Universe is 13.8 BILLION years old, 100 million times older than the oldest human. When you and I go out at night there are almost 10,000 individual stars we can see with the naked eye, but the Milky Way has some 400 BILLION individual stars, and there are some 500 BILLION individual galaxies in all the Cosmos. If you and I could somehow take a road trip, from one side of the Milky Way to the other, travelling at the fastest speed possible (the speed of light) it would take us 100,000 years to go from one side to the other —1000 times longer than any human has ever lived. And the entire Cosmos itself is far vaster.

These sorts of factoids are fun to know and think about. They melt your brain, and they can impress your friends and family at a dinner party. But what is always remarkable to me is even though you and I occupy only one small part of the Cosmos in space and time, we have still managed to piece together a story about the history of the Universe — its overall size and content, when it was born, how it has lived its long life to date, and what its ultimate future might be.  As a species, we have only been cognizant of the science we call astronomy for a few centuries, though we have been looking outward into the Cosmos for far longer. But in those few centuries, in just a handful of human lifetimes, we have managed to piece the story together. Even though a human only lives through the merest flash of a moment in Cosmic time, less than a single heartbeat in the life of the Cosmos.  This is a story about how we learn what we learn about the Universe around us and our place within it.

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

I am a professional astronomer, but like most of us, my love-affair with the Cosmos began when I was young. I would spend long hours out in the backyard, laying on the ground trying to learn my constellations with an old beat-up paper star wheel. We didn’t have a telescope (they were expensive), but my mom is an avid birder and she had an old spotting scope. She used to let me take it out in the backyard and put it on an old card table, and I discovered there was far more to the Cosmos than my naked eye could see. I looked at the Moon and discovered craters, and mountains and sinuous canyons. I looked at the brightest points of light I could see, and found out they were Mars, and Jupiter, and Saturn — other worlds, tantalizingly close, but so very far away. There were other things to discover as well.

My Mom’s spotting scope (she still has it!). This is the first telescope I ever looked at the sky with.

In the corner of the sky we call Andromeda, there is a smudge of light that looks like a wisp of cloud. It is the most distant object you can see with your naked eye, and we call it the Andromeda Galaxy. It is 2.1 million light years away, which means if you step outside tonight and look at the Andromeda Galaxy, the light that falls in your eye and makes its impression on your mind is ancient light. It left the Andromeda Galaxy 2 million years ago, at a time when the most advanced hominids on Earth were Australopithecus, and the world was dominated by mega-fauna like sabre-toothed cats (smilodons) and mastodons. This is one of the fundamental truths in astronomy: looking out is looking back in time, and the farther we can look, the more about the long history of the Cosmos we can discern. As astronomers we are always on an epic quest to build better tools to help us probe farther out into the Cosmos. 

My first astronomical telescope, an 8-inch reflector I built called Albireo, based on Richard Berry’s excellent book “Build your own telescope” .[Image: Shane L. Larson]

Let’s look back to the time when I decided to become a professional astronomer, sometime during my early years in college. Thirty years ago, in 1988, I was already improving my backyard astronomy. I’d left my mom’s spotting scope at home, and after not too long had built my own telescope. It was bigger than my mom’s spotting scope, and could see much more of the Universe. At the same time, the largest telescope used by professional astronomers was the 5-meter (200-inch) Hale Telescope on Mount Palomar. At that time, it was the largest telescope in the world, a title it had held for 40 years since it was built in 1948. Astronomers are still using it today.

The 5-meter Hale Telescope on Mount Palomar was the largest telescope in the world for 40+ years. This image was taken in the dome on a night in 2009 when one of our observing runs was clouded out. Astronomers still use this telescope today. [Image: Shane L. Larson]

So what do astronomers do with these great machines? On any given night, whether you are looking through a backyard telescope, or looking through a telescope like the Hale, the sky looks much like it did the night before. The stars are still where you remember them, living out their lives slowly, changing little. We find new and interesting things, of course, but what we are often most interested in are the unexpected events — energetic and dramatic events that appear in the sky and then are gone. Astronomers call such things “transients.” Consider a “supernova.” One of the things we have learned over the past century is that stars, like people, are born, they live long lives, and they ultimately perish. When the most massive stars reach the ends of their lives, they die in a titanic explosion that, for a few brief days or weeks, sheds enough light to be visible in the night sky. The last time an explosion like this was seen in the Milky Way was in 1604, before the first telescope was ever used to study the sky!  Four hundred years ago, we didn’t know what supernovae were, but the events were momentous enough to note down.

An astrolabe from the Adler Planetarium collection, showing the Supernova of 1604. [Image: Adler Planetarium, notations from Pedro Raposo]

You can find written notations of the 1604 supernova in paper star atlases of the day, but one of my favorites is shown in the astrolabe above, which is part of the Adler Planetarium’s historical collection. An astrolabe is a mechanical device used to visually measure the positions of stars in the sky by eye. They are elaborate and intricate machines, but also stunning and artistic in their elegance and form.You’ll see on the upper right ring of this astrolabe that Supernova 1604 is marked, preserved forever in the solid copper record of the day. You’ll notice there are other transients on this astrolabe, including the previous supernova observed in the Milky Way (Supernova 1572), as well as the great comet of 1618.  My colleague Pedro Raposo, an astronomy historian at the Adler Planetarium, points out that depicting supernova and comets on an astrolabe is an indicator of how our understanding of the Universe was evolving. At that time, we didn’t know what supernovae and comets were. Their nature was widely debated, with many believing they were atmospheric phenomena. The fact that they were recorded on a mechanical starmap is an indicator that we were slowly coming to the understanding that these events were in the deep, cosmic sky. Our views about the Cosmos were changing.

Supernova 1987a, imaged by the Hubble Space Telescope in 1995, eight years after the explosion. [Image: STScI/NASA/ESA]

Now spool ahead to the 1980s. In 1988 we understood much more about supernovae than we did when that astrolabe was built, but we had never been given the opportunity to study one up close. In the entire 400 year history of telescopic astronomy, there has not been a supernova here in our own galaxy, close enough for us to see all the fine details and study how stars reach the end of their lives. But on 23 February 1987, there was a supernova not too far away, in a small galaxy next door to the Milky Way, called the Large Magellanic Cloud. We called it Supernova 1987A, and it was visible to the eye for several months. Astronomers could see it in their telescopes, and still today the most powerful telescopes can detect the faint echoes of light coming from the explosion.

But SN1987A was special for another reason. When a star dies in a supernova, it not only sheds light, it also releases a cosmic rain of particles called neutrinos. When this supernova exploded, 10⁵⁷ neutrinos were released (that’s 100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 neutrinos!), bursting out in every direction in the Universe. Neutrinos are notoriously hard to detect because they tend to go blasting right through matter as if it isn’t even there. When the neutrino burst from SN 1987A reached Earth, 30 trillion of them went through me and you and every other person on planet Earth, and we didn’t even know it! But astronomers had been thinking about this for a long time, and had constructed a special observatory — a neutrino telescope.

The Kamioka Observatory “KamiokaNDE” experiment, one of the neutrino observatories that captured a few of the neutrinos from SN1987a. [Image: ICRR/University of Tokyo]

A neutrino telescope is not like an ordinary telescope, because neutrinos are very difficult to capture. Instead neutrino telescopes watch for neutrinos interacting with other things. In 1987, the worlds largest neutrino telescopes were enormous tanks of very pure water underground. Sometimes when a neutrino goes through these tanks, their interaction with the atoms in the water generates bursts of light that can be detected with very sensitive cameras lining the inside walls of the tank. In the hours right before telescopes detected the light from the supernova, 25 neutrinos were seen in detectors around the world. Only 25 neutrinos from all the 10⁵⁷ that were released in the supernova, but it was enough to convince astronomers they had seen neutrinos from the supernova. This was the first time in history that astronomers had detected an astrophysical event with light AND particles; this was the beginning of what we now call “multi-messenger astronomy.” It was a watershed moment in our quest to probe the Cosmos — we had, for the first time, used two machines to probe the Cosmos using different pieces of information together to make one story. It was the beginning of a new way of thinking and learning about the Universe, and it is a story that is still going on today.

This was the frontier of astronomy 30 years ago. In our next post, we’ll fast-forward to today and ponder how we plumb the deep sky with all our modern technology and combine it with the meager knowledge that we’ve gained over the past few decades.

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This post is the first 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 (this post)

The Cosmos in a Heartbeat 2: Coming of Age

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

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.

I also put this post up today to celebrate the occasion of Carl Sagan’s birthday. I, like many around me, was inspired at the right moment by exposure to Sagan’s “Cosmos: A Personal Voyage”. Friday (9 Nov 2018) would have been Carl’s 84th birthday. He left us more than 20  years ago now, but I still hear his voice when I think about and ponder the deep mysteries of the Cosmos around us. Happy birthday, Carl.