Tag Archives: Hubble Deep Field

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?


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.

Feeling Small in a Big Cosmos 01: Vastness

by Shane L. Larson

One of the great pleasures in my life is that I am both a professional as well as an amateur astronomer. I spend my days, like many of us do, behind a computer keyboard, staring at a computer screen. I get to think about things that are cool, like black holes and the death spiral of binary stars, and whether or not we can hear the faint whispers of gravity washing over us from some unimaginably distant cosmic shore.

There is nothing quite like standing out in the dark and seeing the Cosmos with your own eyes. [Grand Tetons, by Royce Bair; http://NightScapePhotos.com/ ]

There is nothing quite like standing out in the dark and seeing the Cosmos with your own eyes. [Grand Tetons, by Royce Bair; http://NightScapePhotos.com/ ]

But when I go home, I like to spend long hours of the night out under the stars, in deep personal communion with the Cosmos. Stand out in your backyard, or in a dark mountain meadow, and look up. The sky is deep and vast, studded by thousands of stars, tantalizing bright and inviting, but inexorably far away. If you’re lucky, you can see the Milky Way striking up from the horizon, soaring overhead into the velvet darkness, holding the sky up over your head. I find it deeply comforting to lose myself in that view, to let the Cosmos envelop me in its embrace; some part of me knows “this is home.”

The deep connectedness we often feel with the Cosmos is tempered by another realization: that we are small in the face of the vastness of the Universe. It is an ephemeral and unsettling feeling that is hard to explain and vocalize, but in the opening scene of Cosmos, Carl Sagan captured it perfectly, writing

“The size and age of the Cosmos are beyond ordinary human
understanding. Lost somewhere between immensity and eternity
is our tiny, planetary home, the Earth.”

Beyond ordinary human understanding. We can quantify the scale and age and makeup of the Cosmos, but most of the numbers we are forced to use are big — crazy big! Well outside the boundaries of our everyday experience. Numbers so far outside our everyday experience that to simply state them is almost meaningless, because when we hear them said aloud, our brains fail to process what we are really saying (or hearing). Saying and hearing the numbers fails to adequately capture what we instinctively know, but can lyrically convey one person to another with words that are poetic, but somehow deeply meaningful: somewhere between immensity and eternity.

Our understanding of the vastness of the Cosmos starts not by looking outward, but rather by looking inward. This photograph is one of the most iconic images of the Space Age, known as “The Blue Marble.” There have been many versions, updated every few years as new and better images become available. It looks, for all the world like a child’s blue, glass marble.

The Blue Marble, 2012. [NASA]

The Blue Marble, 2012. [NASA]

There are very few people who, when presented with this photograph, don’t recognize it as the Earth. But here is something to consider: to actually see the entire Earth at once, as it is presented in this picture, you have to be tens of thousands of kilometers away. In all the history of our species, there have only ever been 24 people who have seen the world this way: the Apollo astronauts who made the voyage to the Moon and back.  The rest of us have only become familiar with this image of our small, fragile world though their words, their memories, their pictures. Since that time, now approaching 50 years in the past, the picture has been updated and refined, not by human eyes, but through the lenses and electronics of robotic emissaries, cast out into the night to make voyages that we humans seldom seriously pursue.

The most common and fastest modes of transportation most of us will ever encounter.

The most common and fastest modes of transportation most of us will ever encounter.

This small, blue world is the starting point for all our voyages into the Cosmos, whether they be on ships adapted to the abyss of space, or on wings of thought, unfettered by physical separations in time and space. One way to think about the size of the Cosmos is to imagine making a voyage of exploration. In the stack of notebooks on my desk is one non-descript composition notebook marked “Destinations.” It contains within its leaves lists and notes of destinations on Earth that, given time and freedom, I would love to visit. Kind of my own personal Atlas Obscura.  Many of those destinations can be reached using an automobile, the transport du juor for most of the modern world. Most of us have been in an automobile, and have traveled regularly at a speed of say 100 kilometers per hour (about 60 miles per hour).  By contrast, many of the other destinations can only be reached using the air travel network that girdles our world, travelling by jet aircraft at about 900 kilometers per hour (about 550 miles per hour). Few of us have had the opportunity to travel faster, in a military jet or by rocket.

British astronomer, Fred Hoyle, once remarked “Space isn’t remote at all. It’s only an hour’s drive away… if your car could go straight upwards!” He’s right — the boundary of the Earth’s life-sustaining atmosphere is not that far over our heads. If our cars could drive straight up, we would be off on an epic, Cosmic road trip unlike any other before. Let’s consider a few interesting mileposts, and what their entries might look like in my Destinations notebook. My roadtrip car of choice: a Yugo.


Consider Earth orbit — the first stop on the way to anywhere beyond the Earth. For your spaceworthy Yugo, the journey up will be a few hours, and only 23 minutes at the speeds of a passenger jet. By contrast, it took the space shuttle just under 10 minutes to reach orbit.

The Moon was 4 days away if you travelled on Apollo; to drive your car would take 5.4 months of non-stop driving, and just over 17 days by jet. Here, we begin to get the inkling of why exploring the Cosmos is hard — at the speeds of everyday life, even the closest destinations are far away.

Spacecraft take 6-12 months to reach Mars by rocket. Driving in your car would take more than 106 years — longer than a human lifetime. If you left for Mars in a jet when you entered first grade, you’d make it just in time to have your high school graduation on the Red Planet.


Pluto has long been the outermost sentinel of the small neighborhood we call home. The New Horizons spacecraft has taken 9 years to fly there, and as of the time of this writing is less than 2 weeks away from its flyby encounter. If the ancient Egyptians had left for Pluto in a spacefaring Yugo, they still would not have arrived— the voyage by car takes almost 7000 years to complete; the voyage by jet takes 740 years.

Beyond the boundaries of the solar system, voyages by ordinary means can be computed, but they become utterly meaningless in terms of timescales. The center of the Milky Way is 26,000 lightyears away, which would take 31 billion years to reach at the speeds of a passenger jet — more than twice the age of the known Universe. The Andromeda Galaxy, the nearest spiral galaxy to the Milky Way, is 2.5 million lightyears away, but it would take us 3 trillion years to reach via jet.

We can compute these times, we can say these words, but our eyes glaze over and we let the words for the immensity of the Cosmos slip by us with little regard for what they really mean. The size of the Cosmos is beyond ordinary human understanding.

The Hubble Space Telescope. Arguably the most capable and successful telescope ever built by humankind.

The Hubble Space Telescope. Arguably the most capable and successful telescope ever built by humankind.

Despite the fact that we can’t voyage across the Cosmos, we can look. The most capable and accomplished telescope the human race has ever built is the Hubble Space Telescope. In its 25 year lifetime, it has seen farther than any telescope before, with tens of thousands of scientific papers published using its data. One of the most remarkable tasks we set before it was the creation of “deep fields.”

Consider the evening skies, shortly after 9pm in January. The constellation of Orion, the Hunter, lies just to the east of the meridian (an imaginary line, running from due north to due south in the sky). Striking out from his western knee is the long and sinuous constellation of Eridanus, the Great Sky River, that winds and wends its way around a non-descript constellation known as Fornax, the Furnace.

Location of the Hubble Extreme Deep Field, between Eridanus and Fornax.

Location of the Hubble Extreme Deep Field, between Eridanus and Fornax.

Between Fornax and one of the bends of Eridanus there is a small, blank patch of sky. Like many patches of the sky, there is nothing there visible to the naked eye. Even far from the city lights, if you stare into the void there, you will see little. To make a Deep Field, we take Hubble, the most storied telescope in history, and stare at one empty spot in the sky. For many days on end. In the case of this lonely spot on the banks of Eridanus, Hubble stared for 23 days.  The result is one of the most startling and revelatory pictures taken in human history.  It is called the Hubble Extreme Deep Field (XDF; NASA page here).

The Hubble Extreme Deep Field (XDF).

The Hubble Extreme Deep Field (XDF).

As you can see, the blank patch of sky is not so blank after all. Every fleck of light, every smear of something in this picture is a distant galaxy, a remote shoal of stars and planets and gas and dust, and just maybe, other intelligent beings staring up at the sky.  All told, in this single image, there are about 5500 individual galaxies. The faintest are 10 billion times too faint to be seen with the naked eye; it took Hubble, the most powerful telescope we’ve ever built, 23 days to see them.

And what have we learned from this picture of the Cosmos? All told, there may be as many as 500 billion galaxies in the entire known Universe. We know that the Universe is 13.7 billion years old, but the oldest galaxies we’ve seen formed soon after the birth of the Cosmos, about 13.2 billion years ago. Big numbers, huge numbers. Numbers beyond ordinary human understanding.

The Cosmos is ginormous (that’s a technical term). It is easy to be overwhelmed when faced with the enormity of it all. But you should also take heart. One of the most remarkable things about the Cosmos, one of the most remarkable things about our species, is that we can figure it out. Despite the size and vastness we have managed to see and understand remarkable and astonishing things about our home, and are capable of pondering the implications of our existence in the Universe. Next time, we’ll explore some of those discoveries and ponderings.


This post is the first in a series of three that capture the discussion in a talk I had the great pleasure of giving for Illinois Humanities as part of their Elective Studies series, a program that seeks to mix artists with people far outside their normal community, to stimulate discussion and new ideas for everyone.

Part 1: Vastness (5 July 2015)

Part 2: Discovery (11 July 2015)

Part 3: Proverbs (20 July 2015)

Illinois Humanities taped this talk and you can watch it online;  many thanks to David Thomas for doing the videography!