Category Archives: practice

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

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.

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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.

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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)

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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!

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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)

 

A Majestic End for a Faithful Friend

by Shane L. Larson

We live in an age where digital technology can make anything seem real. Movies have become immersive experiences where any landscape, real or imagined is possible. Physics defying stunts are rendered on screens as tall as buildings and with sound louder than thunder. Creatures long extinct or completely imagined spring to life, and actors long since passed from the world magically return to the screen, appearing as they did in their youth. Anything seems possible, and the boundaries of reality are blurred, to say the least.

Anything can be given realism with modern technology, whether they be long dead creatures, imagined aircraft, or an architectural plan for a new building. [all images from Wikimedia Commons]

We are so used to this, that when confronted by real pictures of the real world, we often forget what we are looking at. Fantastic and awe-inspiring pictures slip past us and don’t always capture our attention. Photographers capture massive migrations of animals across the land and sea, forlorn sights of abandoned corners of our cities, and the vibrant colors of rainbows and autumn leaves. When we see those pictures, at just the right moment, we experience a visceral moment of joy and set our phone screens and computer desktops to the image, to remind us of that moment of wonder. But more often than not, we don’t remember that real pictures of the real world can evoke emotional responses in us. Some small part of our brain remembers, of course, else we wouldn’t takes selfies in front of restaurants where we enjoy fantastic dinners, or pictures of sunsets against the skyline of our backyards.

On many days, as the woes of the world sidle past me on my computer screen, I am reminded of something that I became aware of in my youth: the true masters of real pictures of the real world are the folks at NASA. They have long been part of the storytelling narrative, reminding us that we are part of a far larger Universe, showing us that with concerted effort and imagination and perseverance, we can overcome tremendous obstacles, solve incredibly difficult problems, and discover that the world around us is filled with unimagined and awe-inspiring grandeur. The Cosmos is alive and breathing around you, reminding you that you are part of something greater that the usual bibble-babble washing out of your device screen.

NASA’s digital artists are masters of putting us at the center of the action, even if it is impossibly far away. L to R: Curiosity skycraning onto Mars; Juno arriving at Jupiter; Cassini arriving at Saturn. [Images by NASA]

In the last few years, our friends at NASA have upped their game. Not only have they regaled us with real pictures of the real world, but they’ve picked up the story-telling torch, and as masterfully as any filmmaker in the world catapulted us into the drama of exploring the Cosmos. You may remember this when they told us about the Seven Minutes of Terror as we lowered the Curiosity rover onto Mars using a robotic, rocket-powered skycrane. Last year, they told us the tale of returning to the unknown regions around Jupiter with a hearty spacecraft called Juno, diving into the radiation belts where anything could happen. But recently, they turned their attention to a far-away world called Saturn, and a steadfast spacecraft we sent there called Cassini….

Saturn has been known to humans since antiquity, one of the bright moving lights in the sky known as the planētes asteres, the “wandering stars.” Like the other naked eye planets, Saturn moved slowly among the stars, tracing out a path along the band of constellations known as the Zodiac, cementing itself in the folklore and mythology of sky-gazers who watched it closely. In the 17th century, the era of Saturnian exploration began when the first telescopes were pointed skyward. The first fuzzy, warbling views of the world showed it was not like the stars at all. Telescopes improved rapidly, as did the views they showed of this far away planet, until at last we discovered the truth — Saturn was magnificently bejeweled by a brilliant, encircling ring. Since that time, Saturn has reigned supreme among all the planets for the awe it evokes at its splendor and beauty. More than any other planet, it looks like it is supposed to look. Today, millions of telescopes around the world are set-up in backyards and on sidewalks on clear nights, giving ordinary people like me and you views of one of the Cosmos’ great spectacles — you can have your own Saturn Moment.

View of Saturn you will have through a modern backyard telescope, taken with an iPhone [Image courtesy of Andrew Symes]

Like most things in space, Saturn is unfathomably far away. At a distance of 1.3 billion kilometers from Earth, it would take you about 1400 years to drive to Saturn’s orbit in your car, or about 150 years to fly there at the speed of a passenger jet. We are, by and large, restricted to staring at it from afar, gleaning what we can from the meager light gathered in our telescopes. The arrival of the Space Age put a new possibility on the table: travelling across the void. Suddenly, we had the chance to see Saturn up close.

While there are effervescent dreams to send humans, Saturn is still too distant to imagine easily crossing the void ourselves, so our attention has been focused on sending quasi-intelligent emissaries in our stead: robotic explorers whose sole purpose is to gather as much information and take as many pictures as possible, and transmit all of that information back to Earth.

Our robotic emissaries, Pioneer 11 (left) and Voyagers 1 and 2 (right). These are the only spacecraft to have ever visited the gas giant worlds of the Solar System. [Images by NASA]

In the 60 years since the start of the Space Age, only 4 spacecraft have ever visited Saturn. The first was a resolute robotic explorer called Pioneer 11.  In 1979, it flew by Saturn skimming through just 20,000 kilometers above the cloud tops, returning the first up close pictures of Saturn, but only a few. It was followed by Voyager 1 in 1980, and Voyager 2 in 1981. The Voyagers returned wide planetary views of Saturn that became iconic to an entire generation of humans, and showed us an ensemble of moons that are each unique and tantalizing, demanding their own careful program of exploration. All of these missions flew past Saturn, returning quick passing views before sailing onward. Today, Pioneer 11 and Voyagers 1 and 2 are on an unknown voyage, destined to drift in the great cosmic dark between the stars for a billion years.

Closeup views of Saturn by Pioneer (left) and Voyager (right). Their time with Saturn was short because they were doing flybys (try taking a picture of your friend on the sidewalk as you drive by at 50 miles per hour…). [Images by NASA]

The most recent of the quartet of august explorers is a two tonne spacecraft called Cassini. It spent seven years crossing the void to Saturn, and has spent the last 13 years circling Saturn, probing the ringworld and its remarkable moons. Twenty years ago, it was cocooned up inside its rocket, and hurled into space. No human has seen it since.

This image is one of the last pictures taken of Cassini in 1997, before launch; the whole spacecraft, together with a few of the people who gave it life. Not soon after, the rocket fairing was lowered into place and closed, cocooning Cassini inside. That was the last any human ever saw of it. [Image by NASA]

For more than a decade, we have been treated to remarkable images, ranging from the strange divided faces of Iaepetus, to the mangled surface of small, tumbling Hyperion. We saw stunning views of the blue-white ice of Enceladus, and ephemeral views of Saturn and its rings, backlit by the distant Sun.

The images returned by Cassini have been stunning, and are far too numerous to do justice to here. A few favorites include: Hyperiod (top left), Enceladus (top center), Iapetus (top right), and Saturn backlit by the Sun (lower). [Images by NASA]

But never among these has there been an image of Cassini itself. Unlike its siblings, the Mars rovers, Cassini cannot take a selfie. But our artists have continued to insert Cassini into imagined views of the Saturnian system, seen as if we were sailing along side it, snapping pictures for the family photo album. Cassini cruising over Titan; Cassini plummeting through the ice plumes of Enceladus; Cassini looking back toward a distant blue star that is Earth.

Artist imaginings of Cassini during its decades long exploration of Saturn. [Images by NASA]

Now, after a two decade journey, we are nearing the end. Cassini’s tasks are nearly over. Unlike Pioneer 11 and Voyager 1 and 2, Cassini is bound to Saturn forever; it will not embark on a lonely voyage to the stars, and in fact, it can’t: there simply isn’t enough fuel in its rockets. Instead, the humans who lovingly crafted it and meticulously planned its journey have planned a magnificent send-off. We call it The Grand Finale. The end of the journey is stunning, worthy of an adventurer as bold and brave as Cassini. But we won’t be able to see it, so once again we turn to our artists to illuminate the images in our minds eye.

Some images from Cassini’s Grand Finale. (L) Saturn’s polar regions, up close as Cassini loops over the top of the planet for another ring pass. (C) One of the highest resolution images of the rings ever taken. (R) The small moon Daphnis, carving out a corridor in the rings. [Images by NASA’s Cassini Imaging Team]

In a series of slowly descending orbits, Cassini will voyage closer to Saturn than any spacecraft before. Looping high over the planet, it will plunge down through the rings for the first time, then loop back around and do it again. Over and over again, it will pass through the rings and skim the top of Saturn’s atmosphere. In all, the Grand Finale consists of just more than 22 orbits. On each orbit it dutifully records what it finds, and relays that information back to us here on Earth. Already we have received stupendous views of the rings, of the cloudtops from closer than we’ve ever seen, and the nearby moons framed by a sky simultaneously more majestic and more alien than any we could imagine in a Hollywood studio.

But at the very end, when there is no where else to go, Cassini will finally succumb to the inexorable gravitational pull of Saturn, and be drawn down into the atmosphere. Travelling more than 75,000 miles per hour, it will burn up in a colossal fireball. One of a thousand meteors that might hit Saturn on any day, but this one from a nearby world. We won’t see Cassini. As it falls, it will be linked to Earth only by the tenuous thread of its radio link, faithfully relaying the last of its observations as it sinks forever into the ocean of Saturn’s atmosphere.  At some point, we don’t know when, Cassini will be gone. With no one to see it, Cassini will disintegrate into nothing. Out of our sight, the last of our dreams and aspirations for Cassini will come to an ultimate end.

Will will mourn. But always we will return to the vast photo album we have assembled over its 20 year life. Like a long time friend departing for the other side of the veil of death, we can’t help but be simultaneously overwhelmed by sadness together with admiration for everything that this little robot has accomplished, against all odds. Cassini has forever transformed our understanding of Saturn. Saturn is a real place, as much a part of the story of our solar system and our home as anything we have ever seen.

Once again our artists capture what we cannot see, rendered in NASA’s End of Mission video, using the tools of entertainment to tell us the story of our long departed emissary in it last moments over Saturn. More than any other art or video I’ve seen, they’ve succeeded in evoking how truly huge and majestic Saturn is, and how tiny Cassini is by comparison. All that we know, all that we’ve discovered, we owe to a tiny robot immeasurably dwarfed by the planet it has so faithfully explored.

You owe it to yourself to go watch this video; reflect on all that Cassini is and was, and know that we are capable of doing tremendous things.

Ad astra per aspera. Fare thee well, Cassini.

Total Eclipse: On the Far Side of Totality

by Shane L. Larson

How do you describe the indescribable?

I’ve been a skywatcher for more than half of the years of my life. I’ve literally spent thousands of hours with my telescope, watching the sky, making sketches to remind me of what I saw, keeping notes about appearances, and making lists of favorites to look at again. I’ve seen the rings of Saturn, and the Great Red Spot. I’ve observed supernovae, seen comets stretch across the sky, and watched the aurora borealis storm overhead. I’ve seen a transit of Venus, a once in a lifetime event.

But nothing prepared me for what I saw on Monday, standing on a hillside in Casper, Wyoming. For a brief two minutes, the Moon covered the Sun in the total solar eclipse of 21 August 2017.

Our morning started early, arriving at 5:30am. We weren’t tired now; that was later, after the eclipse was over and the adrenaline wore off! [Image by S. Larson]

My family and I, together with eight of our long time friends, set up on the grounds of Casper College, together with a vast number of our amateur astronomy colleagues who had been in Casper for the  2017 Astrocon Convention. The eclipse was due to start at 11:42am MDT, so we arrived on site early to set up: 5:30am!

By 6:00am the horizon began to glow with the scarlet tones of sunrise, and at 6:19 the Sun rose slowly over the distant horizon. We couldn’t see it, but we knew the Moon was right there too, steadfastly churning along its orbit, its shadow streaming through space, like a needle waiting to poke the Earth.

Sunrise and the appearance of the Sun. This was the moment when we knew in our cores that we were going to witness the total solar eclipse, without fail. [Images by S. Larson]

We had a row of tripods — some set up to image, some with binoculars, some with telescopes, all with solar filters. Every one of us had eclipse glasses that we constantly watched the Sun with, waiting for the first moment when the Moon would slowly begin to move between us and the Sun.

Eclipse glasses. This is pretty much how we looked all morning once the Sun came up. [Images by S. Larson]

We knew we were in for a wait, as the eclipse wasn’t due to start until 10:22am, and totality wouldn’t start until 11:42:42am!  So we paced back and forth restlessly. We took selfies with each other. We joked around. We checked the traffic, wondering if the slug of red between Denver and Cheyenne would make it to the path of totality on time. We played games. We make cookie art to track the eclipse.  You know — normal nerd herd stuff.

Just passing the time, tracking the eclipse by making art with cookies. [Images by S. Palen (L) and K. Larson (R)]

The folks down the row from us had an old Astroscan telescope, outfitted with a DIY homebuilt funnel projection screen (here are instructions from NASA) that was ideal for letting everyone see what was going on, and for taking pictures of what the Sun looked like during the partial phase of the eclipse. There was an excellent group of sunspots arcing across the middle of the Sun, and another small group down near the limb.

Our observing neighbors had an Astroscan fitted with an observing funnel (top left). The Sun had some great sunspot groups that day (top right). The screen made it easy to see the progression of the partial eclipse (lower 4 photos). [Images by S. Larson]

We also watched the progression with pinhole projections, looking at the shadows of anything with tiny holes in it. Every one showed a dazzling array of small crescent Suns, slowly being eaten by the Moon.

“Pinhole projection” is an easy way to enjoy the progress of the partial eclipse. We used a cheese grater and a Ritz cracker (Left), and also watched the dappled light in the shadows of the trees (Center and Right). [Images by S. Larson]

And then, we knew the moment was coming. We were all watching. The light got really flat and dim all around. It started getting darker, quickly. At the last moment before the Sun was completely covered, the left side burst out in a brilliant flare we call “the diamond ring.” Simultaneously, I remember the right side illuminated with a sharp edged circle, rimming the edge of the Moon. And then the Sun was gone. The total solar eclipse had begun.

We were on that hillside with maybe a thousand other people, and it erupted with cheering, screaming, whistling, and shouts of joy and astonishment. There are a million photos on the web of these precious few moments of darkness, suffused with the effervescent, gossamer glow of the Sun’s corona. They are fantastic pictures, but none of them capture everything I remember now in my mind’s eye.

The shapes are right, with two streaming horns pointing up and to the right and one down and to the left. Many of them show the bright red spot of a solar prominence peeking out from behind the limb of the Moon. A few that have been processed show the amazing interlaced structure in the corona.  My lifelong observing buddy (Mike Murray) and I agreed that the word we would have used to describe the view is translucent.

The best representation of the color I remember is the translucent blue of this plastic, in the middle of this cup (above the dark blue in the bottom). [Image by S. Larson]

But even more what I remember was it did not look white to me. It looked kind of pale blue. I’ve observed a lot of objects in the sky, and the diaphanous light of the corona reminded me all the world of the color in some planetary nebulae or bright, hot stars. I’ve been struggling to find something this same color, or a better way to describe the color. That night at dinner with my wife and daughter, I stumbled on a drinking cup whose translucent plastic comes close to being right.

But in the end, all of these attempts to describe the event fall far short of what I remember. There is nothing quite so profound as standing in the shadow of the eclipse, and it’s over before you even know it. The memory, while powerful, feels slippery — I want to cement it somehow, because it would be horrible to forget what I felt in those few moments. I immediately wrote down my notes (images of them are included at the bottom of this post), but they are pale by comparison to what is in my head. I recently met a psychologist named Kate Russo who studies and writes books about people who watch and chase solar eclipses. She names this feeling we all have about our solar eclipse experiences: ineffable.

I had resolved not to make a considerable effort to set up equipment and try to photograph the event. It was my first total solar eclipse, and I didn’t want to be distracted by the equipment and miss it. I did throw my phone up and snap a couple of pictures, but no more. It is small and grainy, but it looks like an eclipsed Sun. Knowing how fast it went, and how much more I wanted to just LOOK at it, I’m not sure I’ll ever go the route of taking pictures.

Totality. The best photo my iPhone could take? I dunno — the best photo I could take for the time I was willing to spend looking at the screen and not the eclipse! [Image by S. Larson]

In the day since the eclipse, I’ve seen many fantastic pictures of the eclipse from friends. Every single one, no matter how technically awesome it was shot, is spectacular. Why? Because they capture that ineffable moment that every person was trying to capture for their mental review later. Each one is a tiny memento, small and bright, captured on silicon and in digital pixels, that reminds the photographer what it was like to stand, just for a moment, in the shadow of the Moon.

During that same day, I’ve been looking at all those pictures, scrolling through what I had on my phone, talking with my wife and daughter, and talking with friends on social media. Always trying to cement the experience in my head. But quite by chance, I did something that I am thankful for. I set up my video camera (a little Sony Handycam) pointed at the Sun for about a half hour around totality. I didn’t know what it would capture on video, but what I wanted it for was audio.

I couldn’t have asked for any better record and memory of the event than that audio record. I’ve listened to it many times now, and each time I’m transported back to that moment on a hillside in Casper, surrounded by friends and a thousand other of my fellow humans, gazing up at the sky in stupified awe. Nothing shocks my memory with better clarity than this audio. A good friend of mine who is a psychologist in Colorado told me listening to this audio fired off mirror neurons in her brain. Mirror neurons are neural responses in your brain that respond from observing something going on as if you were there doing it yourself.

So I close this meager recounting of my experience with the audio of me and my friends, immersed in the moment. I hope you glean from it some of the joy and awe and ineffable wonder that we all felt standing there for those two minutes, and reminds you of similar moments you may have experienced and shared.

Mirabilis sole!

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I’m a fastidious note-taker. Here are images of my notes I took in the hours immediately after the event.

Notes Page 1. When big things happen, I often have my friends who are with me sign my observing log, so I remember they were there. [Image S. Larson]

Notes page 2. [Image by S. Larson]

Notes page 3. [Image by S. Larson]

Notes page 4. [Image by S. Larson]


Here is the previous post I wrote leading up to this solar eclipse: Total Solar Eclipse: Anticipation (20 Aug 2017)

Here is a previous post I wrote about the astronomy behind a total solar eclipse: Stand in the Shadow of the Moon (25 Aug 2014)

New Astronomy at the New Year (GW170104)

by Shane L. Larson

Newton’s portrait.

January 4 holds a special place in the hearts of scientists — it is Isaac Newton’s birthday (*). Newton stood at the crossroads that led to modern science, and astronomy in particular. He was the first person to build a workable reflecting telescope, a design that now bears his name and for the past 4 centuries has been the dominant type of telescope used by amateurs and professionals alike. Newtonian telescopes have revealed much about the Cosmos to our wondering minds. Newton was also responsible for the first formulation of a physical law that describes the working of gravity, called the Universal Law of Gravitation. Today we use the Universal Law to launch satellites, send astronauts into orbit, convert the force of your feet on the bathroom scale into your “weight“, and a thousand other applications.  There is much to celebrate every January 4.

(L) Aerial view of LIGO-Hanford Observatory [top] and in Google Maps [Bottom]. (R) Aerial view of LIGO-Livingston Observatory [top] and in Google Maps [Bottom].

But on January 4, 2017 the Cosmos celebrated with us, singing in the faint whispers of gravity itself. On January 4, the signal of two black holes catastrophically merging to form a new bigger black hole washed quietly across the shores of Earth, carried on undulating vibrations of space and time. You were very likely unaware of this cosmic event — it happened at 4:11:58.6 am in Chicago. It was a Wednesday morning, and I imagine most people were blissfully asleep. But two of the grandest pieces of experimental apparatus ever built by humans were paying attention – the twin LIGO detectors in the United States.  For only the third time in history, a gravitational wave signal from the deep Cosmos was detected here on Earth.

The signal was the signature of two black holes (a “black hole binary,” in the lingo of the astrophysicists) merging to form a new, bigger black hole. The black holes, by definition, emit no light themselves. However, astronomers know that black holes can often be surrounded by swaths of interstellar gas. The intense gravity and motion of the black holes can stir the gas into a violent froth that can emit light. At the time of the event, the LIGO team sent out alerts to astronomers around the world, who turned their telescopes skyward looking for a tell-tale signature of light bursting from the energized gas. Our best estimate of the location of the event was canvased by 30 groups, in many different kinds of light ranging from radio waves, to optical light, to gamma rays. No tell-tale emissions of light were seen. The only way we were aware of this event is from the LIGO detectors themselves.

An artist’s impression of two black holes insprialling, near merger. [Image by Aurore Simonnet, SSU E/PO]

The Gravitational Wave Signal. We call the event GW170104, named for the date it was detected. The signal from the black holes registered first in the LIGO detector outside Hanford, Washington, and 3 milliseconds later registered at the LIGO detector outside Livingston, Louisiana. All told, it only lasted about 0.3 seconds. The signal exhibited the characteristic chirp shape expected of compact binaries that spiral together and merge — a long sequences of wave peaks that slowly grow in strength and get closer and closer together as the black holes spiral together.

Comparison of the chirp waveforms from the first 3 detected gravitational wave events. LVT151012 was a very quiet event that was not strong enough for LIGO scientists to be confident it was a pair of black holes. [Image: LIGO Collaboration]

During the early inspiral phase of GW170104, where the black holes are independent and distinct, the heavier black hole of the pair was 31 times the mass of the Sun, and the smaller black hole was 19 times the mass of the Sun. Ultimately, they reached a minimum stable distance (in astrophysics lingo: the “innermost stable circular orbit“) and plunged together to form a new bigger black hole. When that plunge happened, the gravitational wave signal peaked in strength, and then rang down and faded to nothing as the black hole pulled itself into the stable shape of single, isolated black hole. For GW170104, this final black hole was 49 times the mass of the Sun.

All of this happened 3 billion lightyears away, twice as far as the most distant LIGO detection to date. Perhaps these numbers impress you (they should) — they tell the story  of events that happened billions of years ago and in a place in the Cosmos that neither you, nor I, nor our descendants will ever visit. We add them today to a very short list of astronomical knowledge: the Gravitational Wave Event Catalogue, the complete list of gravitational wave signals ever detected by human beings. There are only three.

The current Gravitational Wave Catalogue, of all known events [click to make larger].

Take a close look at the list. There are interesting similarities and interesting differences between the three events. They are all black hole binaries. They are all at least a billion light years away from Earth. Some of the black holes are heavier than 20 times the mass of the Sun, and some are lighter than 20 times the mass of the Sun. Astronomers use those comparisons to understand what the Universe does to make black holes and how often.

This is the most important thing about GW170104 — it is a small but significant expansion to this very new, and currently, very limited body of knowledge we have about the Cosmos. These three events are completely changing the way we think about black holes in the Cosmos, forcing us to rethink long held prejudices we have about their masses and origins. We shouldn’t feel bad about that — evolving our knowledge is the purpose of science. LIGO is helping us do exactly what we wanted it to do: it is helping us learn.

What do we know? There are many things we are trying to learn from the meager data contained in these three signals. The new signal from GW170104 in particular has tantalizing evidence for the spin of the black holes, and some neat assessments of how close these astrophysical black holes are to what is predicted by general relativity. But I think the most important thing about the event from the perspective of astronomy is this: the black holes are, once again, heavy. GW170104 is the second most massive stellar mass binary black hole ever observed (GW150904 was the heaviest).

The masses of known black holes. The purple entries are observed by x-ray telescopes, and represent what we knew about the size of black holes before LIGO started making detections. [Image: LIGO Collaboration]

With the first two events we had one pair of heavy black holes (GW150914), and one pair of lighter black holes (GW151226). There is a great mystery hiding there: where do the heavy black holes come from, and how many are there in the Cosmos? Perhaps they are just a fluke, a random creation of Nature that is possibly unique in the Cosmos. But the detection of GW170104 suggests that this is not the case; we’ve once again detected heavy black holes. The race is on to decide how the Cosmos makes them. The answers to those questions are encoded in the properties of the black holes themselves. How many are there? Are they spinning or not? Are they spinning the same direction as one another? How do their masses compare to one another? GW170104 is another piece of the puzzle, and future detections will help solidify what we know.

How can you help? If you’d like to help the LIGO project out, let me direct your attention to one of our Citizen Science projects: GravitySpy. Your brain is capable of doing remarkable things that are difficult to teach a computer. One of those things is recognizing patterns in images. The LIGO detectors are among the most sensitive scientific instruments ever built; they are making measurements at the limit of our capabilities, and there are all kinds of random signals that show up in one detector or the other — we call them glitches.  It is very hard to teach a computer to tell the difference between glitches and interesting astrophysical events, so we have citizens just like you look at glitches and identify them, then we use that information to train the computer. So far citizens like you have helped LIGO classify more than two million glitches, and they put more on the pile every day.

If you’d like to help out too, head over to http://gravityspy.org/ and try it out; you can do it in your web-browser, or on your phone while you’re sitting on the train to work. We have citizens from kids to retirees helping us out. If gravitational waves aren’t your thing, there are more than 50 other projects in science, arts, history and more at http://zooniverse.org/ you can try out!

A representation of the GW170104 signal, from the scientific paper. These are the kinds of images citizens can classify easily, whereas computers sometimes have trouble. [Image: LIGO Collaboration]

PS: For all of you super-nerds out there, let me point something out if you haven’t already noticed. Suppose you were to parse the name of the signal in the following way: 1701 04. Look familiar? The 4th incarnation of 1701; for the cognoscenti, this event shares the designation of the Enterprise-D. 🙂  Until next time, my friends. Live long, and prosper.

(*) When Newton was born, England had not yet switched to the new Gregorian Calendar, which we use today. They were still using the older Julian Calendar, by which Newton was born on December 25; when converted Newton’s birthday falls on January 4 on the Gregorian Calendar.

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

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Many of my colleagues in the LIGO Virgo Collaboration have also written excellent blog posts about the GW170104 event, and the work we do to make gravitational wave astronomy a reality. You should visit their blogs!

Taking a leap (second)

by Shane L. Larson

61 seconds is all it takes
For the 9 to 5 man to be more than one minute late

outfield_playdeepSo goes the song “61 Seconds” on the 1985 debut album Play Deep, from the British rock band The Outfield.  Thirteen times since the release of Play Deep (12 Nov 1985), we humans have added “leap seconds” to our timekeeping, endeavouring as much as possible to keep our continuous record of time aligned with some Cosmic measure of time. In those moments, we had 61 seconds in the “minute.”  On the last day of 2016, we will once again add a second to our accounting of time — at 6:59:59 pm EST (that’s 23:59:59 UTC, for all you time nerds out there), a special leap second will be added. For that one moment, we will all live through 6:59:60 pm EDT (23:59:60 UTC) before the time rolls over to 7:00:00 EDT (00:00:00 UTC). An extra second of revelry on New Year’s Eve, 2016.

A statue of Abu Rayhan al-Biruni in Tehran, Iran. al-Biruni invented the modern second that forms the fundamental basis of our timekeeping. [Image by David Stanley]

A statue of Abu Rayhan al-Biruni in Tehran, Iran. al-Biruni invented the modern second that forms the fundamental basis of our timekeeping. [Image by David Stanley]

The fundamental reason for the leap second is this: all of our timekeeping is based on repeatable events. Currently, one second (according to us humans) passes for every 9,192,631,770 radiative oscillations of a cesium-133 atom.  Originally, however, the second was defined by Persian scholar al-Biruni as 1/86,400 of a solar day, where a solar day is the time it takes the Sun to return to the same meridian on the sky (typically the line from due north to due south).  Our innate sense of time, the basis for our calendars and watches and smartphones, is this one that al-Biruni used.  But here’s the rub — the solar day is not constant, because the spin of the Earth changes over time.

There are a variety of reasons for why the spin of the Earth is slowly evolving. One is the sloshing of the Earth’s oceans due to the rising and falling of the ocean tides. This is caused by the gravitational influence of the Moon on the Earth. What we observe as rising and falling tides are actually bulges of water created by the Moon. As the solid part of the Earth rotates, it turns under and through these bulges, which resist the spin of the Earth in the same way water resists you trying to push your hand through it.  The net result is some of the Earth’s spin is taken away. Other geophysical processes are at work too, including the rebound of the crust since the recession of the ice sheets from the last glacial maximum, the redistribution of water with seasons and long term climate change, crustal displacement from large earthquakes, and so on. The effects are all small, some work together to slow down the Earth, and some work to speed up the Earth. But the net result is this: the actual spin of the Earth is about 0.8 milliseconds (8 ten-thousands of a second) longer than the 86,400 second long days we define with our clocks.

So over time, the spin of the Earth falls behind our clocks, which run ahead a little more every single day. By adding a “leap second”, we are pausing, waiting for the Earth’s spin to catch up.  All things being equal, you and I may not notice. Some computers may flip out (they have in the past when we’ve added leap seconds), but largely I expect most of us will continue sipping our beverages as the Sun goes down, waiting for for 2016 to slip into the past and 2017 to arrive. The leap second will pass by, and we might not even stop to notice.

My copy of "642 Things to Write About," a writing prompt book by the community of the San Francisco Writer's Grotto.

My copy of “642 Things to Write About,” a writing prompt book by the community of the San Francisco Writers’ Grotto.

But yesterday I was thumbing through a book of mine, and it made me stop to think about that leap second a little harder. The San Francisco Writers’ Grotto has published a fantastic book of writing prompts designed to provide a bit of creative fodder for you to practice the craft of writing.  The very first prompt is this: What can happen in a second?

It’s an interesting thought to ponder. Every now and then, we have one extra second to live through (by our reckoning). What could the Universe do with that one extra second?  The answer: amazing things!  There are, of course, far too many awesome things that the Cosmos could do, but here are just a few to get you thinking…

You. Many of the cells in your body are in a constant state of growth and regeneration. To make new cells, your body creates copies of existing cells through a process called “cell division.” In order for this process to proceed, it has to replicate a copy of the genetic material in your cell, which is stored in the long strands of DNA.  All told, a human strand of DNA has about 3 billion molecular base pairs — the building blocks of the DNA ladder. If you could stretch a strand out straight, every strand of DNA would be about 2 meters long. The doesn’t sound very long, until you remember that it is all squished inside a cell, which is too small for your eye to see!  So suppose your cell is duplicating this DNA strand — molecular machines crawl along the DNA strand, reading it out and making a copy. How many base pairs can it read in 1 second?  About 50.  If you do some quick math, 3 billion base pairs divided by 50 pairs per second means it should take about 694 days for your body to replicate a single strand of DNA!  It doesn’t take this long though, because the replication process involves an entire workforce working on reading out different parts of the DNA in tandem; all told, it takes about one hour to complete the replication process — so in 1 second, the teamwork of all the molecular machines working the strand copies about 830,000 base pairs EVERY SECOND.  Is that a lot?  If each base pair were like a letter in your genetic alphabet, 830,000 letters is roughly the number of letters in a 600 page novel.

The Sun, imaged by NASA's Solar Dynamics Observatory (SDO).

The Sun, imaged by NASA’s Solar Dynamics Observatory (SDO).

• The Sun is ultimately the source for most of the energy on Earth. It’s energy is released from nuclear fusion deep in its core, where it burns 600 million TONS of hydrogen into helium every second, releasing energy that eventually makes its way to the surface, making the Sun luminous. At that rate, it will burn a mass of hydrogen equal to the mass of the entire Earth in 70,000 years.

• Suppose you use your leap second to shine a laser beam at the Moon. The beam travels at the speed of light, the ultimate speed limit in the Cosmos. It will almost reach the Moon by the time the leap second is over, but will fall just short by about 56,000 miles. It took Apollo astronauts about 4 days to cross the empty gulf between the Earth and the Moon.

• Every second of every day, 4 or 5 babies are born on Earth. About 2 people die at the same time. The population of our small world is growing, even during our extra leap second.

Unfortunately, many of us spend too many of our seconds in traffic. :-(

Unfortunately, many of us spend too many of our seconds in traffic. 😦

• If you are cruising down the freeway, heading to a New Year’s Eve celebration with your partner or friends, and are travelling at 70 miles per hour (112.6 kilometers per hour), then in a single second you travel 31.3 meters (102 feet and 8 inches). That extra second on the clock gains you an extra hundred feet in your journey.

• You are almost certainly reading this post right now on a mobile device or computer, connected to the vast electronic storehouse of human knowledge called “the Internet.” It is hard to quantify the amount of information on the internet, or what is going on globally at any instant in any kind of meaningful snapshot, but there are Internet Live Stats to give you a sense of the tremendous amount of activity that is jetting electronically around the world. In one second, almost 41,000 GB of data are transferred. That sounds like a lot of information, and it is. Neurologists estimate your brain’s memory capacity to be about one to two million gigabytes — 1 second of time on the internet is roughly 4% of your total brain capacity.

• Like the Moon orbits the Earth, the Earth orbits the Sun, and the Sun orbits the center of the Milky Way. On its journey around the Sun, the Earth is travelling at roughly 108,000 kilometers per hour. In one second, we all travel 30 kilometers farther around the Sun. By contrast, the Sun itself is travelling at about 828,000 kilometers per hour, completing its orbit of the galaxy every quarter billion years. In just one second, you complete 230 kilometers of that journey. When the clocks stall for our leap second on New Year’s Eve, we’ll make it that much farther around our galactic circuit.

There are few objects that personify the modern dependence on electricity as well as a light bulb. The cost for and numerical value for the amount of energy they expend makes them seem somehow diminutive, but recasting that energy in terms of a physical effect on you makes it more tangible.

There are few objects that personify the modern dependence on electricity as well as a light bulb. The cost for and numerical value for the amount of energy they expend makes them seem somehow diminutive, but recasting that energy in terms of a physical effect on you makes it more tangible.

• In one second, every 100 Watt light bulb left on in your house, whether you are using it or not, uses 100 Joules of energy. At current electrical energy rates in the United States (about 12 cents per kilowatt hour), that’s less than 1/1000th of a penny, so it doesn’t seem like a lot of energy. Is it?  This is about the same amount of energy as a 9-inch cast iron skillet dropped on your head from a height of 33 feet (don’t look up — it’s going to hurt real bad when it hits you, because this is a LOT of energy…). Coincidentally, this is roughly the same amount of energy expended by your metabolism to keep you alive, every second of every day — you are the energy equivalent of a 100 Watt lightbulb.

Me and Xeno, burning our extra leap second together taking selfies for the blog!

Me and Xeno, burning our extra leap second together taking selfies for the blog!

• A resting human heart will beat just more than once per second (somewhat less than that, if you’re in great athletic shape). By contrast your cat has a heart rate roughly twice that of a human; in the extra leap second, your cat’s heart will beat twice. Dog heart rates vary by size; smaller dogs have rates like cats, bigger dogs have rates like humans. But everyone will get some extra beats in during the leap second.

Speedcubing is a competitive sport to solve Rubik’s Cube type puzzles in as short a time as possible. To date, there are only 3 successful solves of a classic 3x3x3 cube in less than 5 seconds by a human: Lucas Etter (4.90 sec in 2015), Mats Valk (4.74 sec in 2016) and Feliks Zemdegs (4.73 sec in 2016). Etter and Valk each solved the cube in about 40 turns — just over 8 face turns every second. Zemdegs made 43 turns, a blistering 9 turns per second to capture the world record. Speedcubing is a sport where a leap second is almost an eternity…  The current world record held by a robot is just 0.887 seconds — the machines don’t even need a full leap second to solve a Rubik’s Cube…

Just a few of my cube-style puzzles. The cube in the front right side is a cube designed for speedcubing. I am definitely NOT a speedcuber!

Just a few of my cube-style puzzles. The cube in the front right side is a cube designed for speedcubing. I am definitely NOT a speedcuber!

The list could, of course, go on. You may find it entertaining to think about things that interest you, or ponder things you notice in your life. Ask yourself: what could that extra second be useful for? But after you’ve enjoyed the leap second, sit back in your party hat and puff on your kazoo, and think about the following: time is a real thing. It is clear from the goings on of the Universe around us that time is marching steadily onward; physicists call the evidence of this inexorable stream of time the “Arrows of Time.” But the accounting of time — the division of units of time into units called seconds, and the enumeration of those seconds as they count our way steadily toward tomorrow, are a purely human invention. The Cosmos does not care that there is an extra “leap second” in 2016, not any more than it cares that there is a year called 2016 on some backward blue planet in some forgotten corner of a single small galaxy amidst the 500 billion galaxies that fill the Universe.

The invention of timekeeping, and the invention of the year, and the hour, and the minute, and the second — those are human constructs made with a single purpose in mind: to help us understand the Cosmos around us. These constructs of time are the manifestation of our ability to reason things out, a representation of our ability to consider ideas both complex and abstract and describe and represent them in so simple and understandable of a way that every child, woman and man on the planet can carry a device to tell them how the seconds are passing us by. Which makes me think: it takes about 1 second for me to glance at my watch or smartphone and process what I see. I can waste my extra leap second this  year checking the time… 🙂

Happy New Year, everyone. Enjoy your leap second; I’ll see you back here in 2017.