New Beginnings: Our Darkness (Re)Lit
What clues early in humanity’s search of the sky told the Universe’s story? Emerging from the darkness long ago, what diffuse beacons in the fabric of spacetime offered a glimpse into our place in the cosmos?
When Galileo first pointed his telescope at Jupiter and saw its moons he inevitably would have looked at other parts of the sky. He would have noticed fuzzy patches of light in the sky. Early astronomers could only guess what those fuzzy patches of light were. Collectively, they were referred to as “nebulae”, due to their nebulous forms. Intentional or not, this was the beginning of modern astronomy.
Until the early 1900s, scientists believed the entirety of the universe was contained in what we now call our Milky Way galaxy. They believed that the fuzzy nebulae were much closer to Earth than they actually are. It wasn’t until Edwin Hubble’s observations of Cepheid variable stars in the Andromeda and Triangulum nebulae in the early 1920s that astronomers began to appreciate the size and scope of the universe.
Hubble discovered that those little fuzzy patches of light were entire collections of stars much farther away from us than the rest of the stars in the night sky. In short order, these collections of stars would be referred to as galaxies. That name was natural: the Greeks had already been referring to the fuzzy disc of the Milky Way as a galaxy (the Greeks referred to it as galaxias kyklos which means milky circle; the Latin word galaxias literally means milky way).
Our Milky Way was now one of many, many galaxies.
After changing our notion of what a galaxy is and our place in the universe, Hubble set out to categorize the different kinds of galaxies. Pictured above are many types of galaxies captured by the Dark Energy Camera (DECam). There are at least five or six easy-to-spot galaxies – the edge-on spiral on the right side, the pair of colliding spirals at the bottom center, a big spiral in the top-left, and an elliptical on the far left.
Hubble’s discovery rocked astronomy, and as the fields of astronomy and physics inevitably came together, many new questions emerged. Is the universe static? How did the universe come into being? How old is the universe?
Our current understanding is that the universe is not static. Nobel prize-worthy research conducted in the late 1990s used exploding stars (supernovae) to reveal that the cosmos is expanding at an increasing rate. Some new form of energy (dark energy) is overwhelming the force of gravity between all the massive objects in the universe. The fate of the cosmos is once more brought to light.
So what is driving that expansion? What is causing galaxies to move away from one another, overcoming gravity’s pull? The answer appears to be dark energy. Very little is known about dark energy, but we believe it makes up about 2/3 of the energy in the universe.
And so we are at the beginning again. Our answers lead us to new questions. There are many more questions to answer, and many more measurements to make.
If you’re interested in seeing these galaxies for yourself, point your telescope toward RA 05:00:34 Dec -62deg 4’.
Written by Det. Marty Murphy [FNAL]
Image by Det. Marty Murphy
CSI: Early Universe
For this installment of Cosmic Scene Investigation, we travel to one of the earliest collisions of large-scale structures in the known universe.
A splatter of red (denoting galaxies) lies at the center of this image, and extends toward the lower left. These are the remnants of a cosmic collision. Aeons ago, one group plunged through another at millions of miles per hour, leaving in its wake a wreckage. The galaxy cluster ‘El Gordo‘ is all that remains of this raucous event, which took place less than a billion years after the universe started.
From the deserts of Chile, the Atacama Cosmology Telescope was the first to detect this prodigious system. NASA’s Chandra X-ray Observatory, the European Southern Observatory’s Very Large Telescope, and NASA’s Spitzer Telescope have also collected forensic evidence across the energy spectrum, from the infrared to the X-ray. All put together, we see a system similar to the infamous Bullet Cluster: a pair of clumps converted to a churning, violent amalgam of hot gas, dust and light.
An extremophile in the truest sense, El Gordo is the earliest-occurring cluster of its caliber. Its hot gas is burning at 360 million degrees Fahrenheit (200 million degrees Celsius), and it weighs in at a million billion times the mass of Earth’s sun. Compare this to the Virgo cluster of galaxies, the celestial city that holds our Milky Way and its neighbors. El Gordo’s mass is about the same, but it is over a hundred times hotter.
Dark energy is the name given to that substance, that energy, that is making spacetime spread out faster and faster. In the early universe, the small chunks that make up El Gordo were able to overcome dark energy (if it even existed then) and move toward each other to produce this cosmic crash scene. How many more like it are out there? The case remains open.
To read more about the curious case of the big old cluster, see the peer-reviewed paper and the press release from Chandra X-ray Observatory.
Written by: Det. B. Nord [FNAL]
Image by: Det.’s Nikolay Kuropatkin and Martin Murphy [FNAL]
River of Dreams
The Dark Energy Survey, in its search for distant cosmic secrets, needs many nights of clear sky. Unfortunately, on this night, a river of clouds flowed overhead. We often look so far away to the faintest objects, that a wisping of cottony clouds moving over the Blanco telescope requires extra attention. In these cases, we might change our observing strategy to look at parts of the sky that require less detail.
As we sift through the tons of sediment and the terabytes of data, occasionally the clouds get so heavy and consuming that we must close the telescope dome to preserve the instrument. In these cases, we still use the time wisely: our Dark Energy Calibrations (DECal) team has developed a method to precisely measure and characterize the flow of light through the telescope at every relevant wavelength, and to monitor for any changes in that flow over the years of the survey.
As we fish for light in the sky, we cast a broad net. In the river of dreams, we sift through sediment for celestial gold.
Lights Burning and Churning Through Time
The light is going the distance.
Some celestial (light-producing) objects are farther away than others. The three larger galaxies in today’s image are nearby, located in the Fornax galaxy cluster. As you can see, light comes from other galaxies much farther away: the smaller points are galaxies, too. We measure the patterns in the galaxies that are far away from us and compare that to the patterns of the nearby galaxies. Differences in this pattern give us indispensable clues about how dark energy has affected space-time over the last several billions of years.
And some of the bright points (galaxies) are behind the large galaxy near the center (NGC1374), yet we can see them. What does that tell us about the brightness in different parts of galaxies? If you look closely, we can see background galaxies (those behind) everywhere—except a small patch near the center. This is due to the fact that the centers of galaxies are brighter than their outskirts.
Light from distant regions of space can travel up to billions of light-years, to accidentally land here on Earth — to land on a small spot on the side of a mountain in Chile, where the Dark Energy Camera is waiting to capture it. To measure the expansion of the universe, the Dark Energy Survey needs to measure light from hundreds of millions of galaxies, all differing in their colors, brightnesses and locations. These properties will betray their patterns, which we must decipher.
Light travels the distance, and we’re hunting it all the way.
Written by: Det. B. Nord [FNAL]
Image by: Det.’s Nikolay Kuropatkin [FNAL], Martin Murphy [FNAL]
The Cosmos: A Digital Frontier
Ever since we started looking up, we tried to picture where the lights in the night were coming from as they moved through the universe. What were these objects – fiery stones, gods?
We kept dreaming about and measuring a world that was hard and too dark to see. And then one day, we could see into its depths.
At first, we only looked out with our eyes, and then we captured light on photographic plates of glass, and then we learned to convert the photons of light into electrical signals that we can store and analyze in computers.
When you sit down at the console, the eight-panel control module first looks like a gamer’s dream. And then you look to your left and you see another multi-panel module. These two consoles alone control the hundreds-ton telescope and $50M Dark Energy Camera (DECam) that captures the light from distant galaxies and exploding stars. These two consoles initiate the process of turning the ancient light into the recorded history of the cosmos. But if you want to know what goes on inside the machines, how we cyber crunch the sky, you have to look behind the scenes at the Data Management system that turns photons into bytes.
The Dark Energy Survey (DES) acquires hundreds of images – nearly a Terabyte of data – every night, and will continue to do so for the next five years. After the light is collected and stored, it must be transferred and cleaned before we can mine it for the faint clues of dark energy. As the images are taken, they are transferred via a high-speed pipeline from the mountaintop of Cerro Tololo in Chile to the corn fields of Illinois, where computer clusters at the National Center for Supercomputing Applications (NCSA; image, upper left) perform calibrations and tests to ensure data are free of error and contamination, to prepare them for cosmological analyses.
While we can observe and measure the sky to great depths, a key partner in this endeavor is our theoretical understanding of cosmic evolution. For this, we must create fake universes, with a variety of different parameters, inside these super-computers. DES will simulate several universes, in which we will test the hundreds of thousands, millions of lines of code in preparation for working with actual data. What’s more, we can compare the simulated universe to our own, telling us which aspects we’ve simulated correctly and which parts of our theories are solid, which need revision. Super-computers, like those at NCSA shown in today’s image (top right and bottom), play a critical role in constructing these universes.
It’s amazing how productive watching the sky can be. But, to look out, we had to bring the universe in.
(Hat tip to Tron: Legacy.)
By: B. Nord [FNAL]
Image: NCSA
Hotel Tololo
The dormitory rooms at the Cerro Tololo Inter-American Observatory (CTIO) in Chile cast a stout shadow over the desert fauna in the light of the early risen moon last February. This night’s moon is so bright, it prevents the Dark Energy Camera from looking at that part of the sky. On bright nights like these, we aim the telescope elsewhere, but still looking, still searching for supernovae and distant galaxies.
We start the night’s work early with an inter-continental tele-conference before dinner. After dinner, we prepare the software and telescope until sunset, when the hunt begins. Working through the night (and through a few pots of coffee and bags of cookies), we emerge a few hundred images closer to understanding dark energy and its effects on the celestial objects deep in the night sky. Just after sunrise, we hit the hay, but our minds often keep crunching numbers or sifting puzzles that arose during our observations, as the work from our night bleeds into our dreamscape.
Welcome to Hotel Tololo. We’ll turn the light off for you.
Written by: Det. B. Nord [FNAL]
Image by: Det. B. Nord
360,000 Minutes … How Do You Measure the Sky
On August 31, 2013, the Dark Energy Survey (DES) began its exploration of new realms of the observable universe. For about 100 nights per year, during the next five years, the Blanco Telescope in Chile will scan the sky using the newly commissioned Dark Energy Camera. With 62 highly sensitive detectors (containing about 500 million pixels), DECam will collect light from hundreds of millions of galaxies and thousands of supernovae from billions of years ago, their light leaving faint traces of a cosmos expanding ever faster. Whether the cause is a mysterious dark energy or a change in our understanding of gravity, DES endeavors to discern the nature of our accelerating universe.
We spent the last year commissioning the telescope and camera, performing calibrations and tests to make it science-ready. The 62 detectors are shown in today’s image, taken from one of last year’s preparatory observations. Clicking on this image will take you to an interactive page where you can zoom in on each chip and look at what DES scientists see after each picture of the sky is taken. We will gather thousands of images like this in the coming years.
We now begin a new journey, with many seasons of discovery ahead of us: in photons, after sunsets, past midnight, with lots of coffee… In pixels, in light-years, that’s how we measure the sky.
Written by: Det. B. Nord [FNAL]
Image by: Nikolay Kuropatkin [FNAL], Martin Murphy [FNAL]
The Shape of Things to Come
With so many bright lights out there, it’s a veritable surprise when we remember that most of intergalactic space is utterly empty. It contains about 1 particle per cubic centimeter on average.
Amidst the cornucopia of stars and galaxies sits a distant cluster of galaxies that exhibits a very notable behavior. RX-J2248 (named for the ROSAT X-ray telescope, with which it was discovered) lives at a redshift of 0.35 and has hundreds of red old galaxies, as well as a massive amount of dark matter.
If we zoom in (inset, lower right), we can see the effect that this large amount of matter has on its immediate surroundings and on the fabric of space-time itself. In the center of the inset lies a yellow-ish, beautifully glowing bright central galaxy; this is the hub of RX-J2248. While most of its neighbors shine with a very similar hue, others are as blue as a clear daytime sky. These blue objects are actually distant galaxies, and don’t reside very near the cluster at all. They live far behind it, farther away from us and at higher redshifts.
So how can we see these galaxies? The cluster (galaxies, dark matter and all) has distorted space time: the light will still travel in a straight line, but this straight line is now in curved space. This is similar to how lenses in your eyeglasses distort images and bend the paths of light rays. For this reason, this peculiar phenomenon is called ‘gravitational lensing.’
This image represents the shape of things to come as the Dark Energy Survey gears up to begin its five-year mission. With strong gravitational lenses like RX-J2248, with thousands of supernovae and millions of galaxies and galaxy clusters, we will have the power to explore the nature of dark energy and its impact on our universe.
Written by: Det. B. Nord [FNAL]
Image created by: Nikolay Kuropatkin & Martin Murphy [FNAL]
Star Light, Star Bright
Which star can you see tonight?
Stars live out varied and complicated destinies. From the time of birth, a star’s cores house nuclear fusion reactions that combine lighter elements into heavier ones – e.g., hydrogen into helium, and so on. During fusion, light is emitted. From the core of the Sun, to the pupil of your eye, each ray of light takes a one million-year journey, bouncing off hot plasma on its way out of the star.
This burning can continue for tens of millions to billions of years, depending on the mass of the star. When the burning finally ceases, the light no longer pushes its way out, no longer fights the crushing gravity. For some stars, this disruption results in a massive and violent explosion, a supernova. Stellar material, including the heavier elements, like the calcium in your bones and the silicon in our computer chips, is then blasted into the nearby interstellar medium. In this new enriched region of space, a planet or new star may someday grow.
The pair of images above displays a galaxy, far away from our own, before and after a supernova event. Can you spot the difference? Supernovae often outshine their host galaxies. What’s more they can produce more energy in weeks or months than our own Sun can during its entire lifetime of billions of years.
Supernovae are very well understood. We understand them so well, in fact, that we can use them as buoys in the fabric of space-time: they are precise indicators of how much the universe has expanded at different points in its history.
After a year of commissioning and verifying the telescope and new instrument, the Dark Energy Camera (DECam), we will begin to perform a 5-year census of galaxies, supernovae, and other astrophysical phenomena. Analyzing distances of these objects and recovering patterns, the large-scale structure of the cosmos, we will learn about the nature of dark energy and its impact on the fate of the universe.
Disclaimer: the Sun will not explode. But, in a few billion years, it will grow in size and envelope the inner rocky planets… all except Mars.
Written by: Det. Brian Nord [FNAL], Joe Bernstein [Argonne National Lab]
Image by: Martin Murphy [FNAL] and Andreas Papadopoulos [U. of Portsmouth]
Into the Vortex!
Moonlight illuminates the top-most plateau of the Cerro Tololo Inter-American Observatory (CTIO), near La Serena, Chile—and with it, the Blanco 4-meter telescope dome (middle) that houses the Dark Energy Camera (DECam). Directly above the dome, we see Earth’s south pole, about which the world turns and our celestial sphere rotates, giving us this vortex of starlight. Peering out of our little blue dot, our little snow globe, we also look into the depths of space and into our universe’s past.
Written by: Det. B. Nord [FNAL]
Image by: R. Hahn [FNAL]
Big Sky, Big Beautiful Machines
Sometimes, big ideas need really big machines. Here, we see a rare close-up of the Dark Energy Camera (DECam) and most of its components. Over the course of about 10 years, hundreds of scientists and engineers from institutions across the world designed, built and calibrated the major components of DECam—an optical lens barrel, a hexapod, a filter changer, a shutter, CCD sensors and control electronics (from lower right to upper left).
In the image, DECam is not yet actually on the Blanco Telescope, which is in Chile. Before being installed there, it was assembled at the Fermi National Accelerator Laboratory (FNAL) in Batavia, Illinois in a test facility. The operations team performed tests to make sure that the multiple components came together and operated seamlessly before shipping all the components to their final location at the Cerro Tololo Inter-American Observatory (CTIO). Fermilab technician Kevin Kuk works on the last elements of assembly before testing.
As we plunge into a new era of science with big data, the needs for diverse skill sets and efficient communication between many scientists becomes increasingly clear. Last century, a few people around a table could design and create an experiment in a very short time, and with it make astounding discoveries. It is unclear how often this will happen in the future: our biggest questions require so many measurements with such high precision, that we need more and more people to work on them. Welcome to a new day in science, welcome to the super-collaborative era.
Written by: Det. B. Nord [FNAL]
Image by: Reidar Hahn [FNAL]
Snowflakes
From bright blue spirals to golden and red ellipsoids, our deep night sky is dotted with nearly innumerable unique galaxies, all teeming with stars and planets. We will use their colors, brightnesses, shapes and even how they are distributed throughout the fabric of space-time to uncover the secrets of dark energy. The veritable cornucopia seen in this image is just one example of the pictures we’re taking.
How many galaxies and how many types do you see? (Galaxies are fuzzy with various shapes, while stars are spherical.)
Roadway to the Heavens: the Signal and the Noise
The Sun has long since set, but the Moon keeps its memory alive. In the moonlight, we traverse this short path up to the top of the mountain each night from one of the small houses where we stay for this 10-night astronomical observing stint. Tonight’s drive offers a clear reminder that the path to new knowledge is as winding and uncertain as the roadway to the heavens.
Most nights, clear and dark skies prevail, and the Dark Energy Camera (DECam) has a clean view to the objects in the sky it aims to see. The signals from stars and galaxies arrive unfettered, uninterrupted. Occasionally, however, clouds block light from the celestial sphere, the Moon outshines it and a turbulent atmosphere redirects it. What’s more, the atmosphere itself is constantly at work, emitting light from across the electromagnetic spectrum.
The atmosphere and Moon represent very important sources of noise when observing, especially when incredibly distant and faint objects are the intended targets: DECam is designed to see light from galaxies that are more than 15 billion light-years away. The goal is to get as much signal as possible, while minimizing the effects of all the noise sources, like those mentioned above.
Clouds, like those seen in this week’s image (20-second integration time), block light from stars and galaxies. Less light means less signal. On some nights, the Moon is too bright for the sensitive detectors in DECam, and we have to point the Blanco Telescope away from the moon. Some of the light from the Moon still bounces around the layers of the atmosphere and trickles into the Blanco field of view. Too much scattered light from the Moon or other sources adds to the noise and obscures the signal. Turbulence in the atmosphere deflects light from the objects we seek: multiple layers of air with different temperatures, moving at different speeds heavily disrupt light paths. Consider how the light of a straw is refracted when it goes into a glass of water. This happens in our atmosphere many many times over.
Over the years, astronomers, engineers and climate scientists have worked more and more closely to understand how weather and climate impact astronomical observations. While we’ve come quite far, and we will be able to do exquisite dark energy science at the Blanco, we know there is more road to pave.
Written by: Det. B. Nord [FNAL]
Image Credit: Det. B. Nord [FNAL]
The Ancient Universe, Untouched
The past can be far, far away, but sometimes it is so close to home. Long ago, the first stars lit up, and hydrogen burned inside them. The hydrogen fused and became helium, which in turn fused into yet heavier elements: through nuclear reactions, the cores of stars birthed all the elements that make up our world. When extremely massive stars with these heavier elements exploded, they sent forth into the universe the stuff that would become new stars, as well as planets, and you and me. These first stars are far away in time and space, but there lives an ancient collection of stars in our galactic backyard that simply grew old slowly and quietly.
Omega Centauri is composed of stars that have elements relatively light in weight—from hydrogen and helium to silicon and neon. However, they are lacking in heavy elements, like iron—the same iron found in our blood and in the steel of our buildings and machines. These stars fused atoms in their cores, but they never grew massive enough to explode, so they just burned on, slowly but surely.
Though Ptolemy cataloged Omega Centauri as a single star 2,000 years ago, it is a dense cluster of several million, very old stars. This globular cluster has been orbiting the Milky Way for 12 billion years, nearly the entire age of the universe. Omega Cen is about 15,000 light-years away from the Galaxy, but just a dozen light-years in diameter itself. What’s more, its millions of stars are separated from each other by just a tenth of a light-year. This is roughly equivalent to a golf ball full of very fine sand sitting at the edge of a football pitch. The nearest star to our solar system is Proxima Centauri, just 4 light-years away—still over 10 times the distance between stars in Omega Cen.
Rediscovered by Edmond Halley (of eponymous cometary fame), Omega Cen (a.k.a., NGC 5139) is a globular cluster located in the direction of the Centaurus constellation. Teeming with millions of ancient furnaces, it is the largest and oldest of the 150 globular clusters orbiting the Milky Way.
Omega Cen is visible with the naked eye and can appear as large as the full moon. It lives at Right Ascension, 13 : 26.8 (h:m) and Declination, -47 : 29 (deg:m), should you choose to seek it out yourself. The image above shows the full cluster in the frame and zoom-in of a small section in the right frame.
Written by: Det. B. Nord [FNAL]
Image Credit: Det.’s M. Murphy and N. Kuropatkin [FNAL]
Fire in the Sky
As day gives way to night, our star plummets into the pacific. We refuel our brains for a night of work and then watch the sun scorch the horizon into darkness. This is our nightly ritual.
After dinner, our crew heads back to the telescope. Some of us take a car up the roads, while others make their way up the winding paths through the clay and dirt. Like clockwork, we pass a family of zorros (“foxes”), who often wait outside the kitchen for tasty scraps. There are more mouths to feed now: this past spring, a new litter of pups appeared. Occasionally, a few viscachas (rabbit-like rodents in the chinchilla family) graze on the rare sprig of fauna in the dry mountaintops and then rest on warm rocks in the fading sunlight.
The Dark Energy Survey (DES) observes during these summer months, and the community has priority access to the instrument during the remainder of the year. DES runs optimally during the dry summer (in the southern hemisphere, lasting from December to February) to avoid atmospheric water absorbing and scattering light from the higher-wavelength portions of the electromagnetic spectrum. We desperately need that light to see older, more distant cosmic structures.
On especially dry evenings, a green flash can be seen in the moments before the last of the sun falls below the horizon. Earth’s prismatic atmosphere scatters the suns rays and splits the light by color. As the sun drops, the spread-out spectrum rolls vertically across our eyes, quickly from red to orange and very very briefly through green.
Celestial objects that DES observes set just like the sun does; between the beginning of night and the time a galaxy has fallen below the horizon there is very little time—from minutes to hours. If the Universe were a year old, humanity has existed for about 20 seconds. We have but mere fractions of a moment to take snapshots of these galaxies and stars that have lived for millions and billions of years and that reside millions of light-years away. Utterly ephemeral, the green flash reminds us of the difficulty of our endeavor, of the challenge of catching light from billions of objects so distant in time and space from us.
Dark Skies Turned Gray: Working in the Clouds
We awoke just after two in the afternoon to the eye-itching grogginess that inevitably follows a long night of observing. The afternoon light just barely peeked through the few windows in our dormitory rooms, located more than 60 meters (about 120 feet) below the Blanco Telescope, where we do our nightly work for the Dark Energy Survey (DES).
As we headed to the lunch-flavored breakfast in the cafeteria we spotted a procession of dark clouds to the southeast. To our dismay, the prevailing winds appeared to be carrying them toward us, and toward the Blanco.
During ‘breakfast,’ comprised of tasty fresh vegetables and sausage, we discussed last night’s observations and logistics, as well as plans for the upcoming night, including speculation about the impact of the potentially turbulent weather.
Wet and tumultuous skies scatter the light from distant galaxies and stars that were otherwise on straight paths toward the telescope. This can cause a blurring of images. For telescopes situated on Earth, the higher the mountain-top site, the better the chances of avoiding atmospheric disruptions. The Cerro Tololo Inter-American Observatory resides at about 2200 meters (or 7200 feet) and it enjoys clear, dry skies the vast majority of the time.
Occasionally, mother nature reminds us of her unpredictability and how precious each photon is. With only eight hours of night out of every 24, we need all the darkness we can get. On this afternoon in the early Chilean spring season, our hopes would succumb to the fickle weather. After lunch, we left the cafeteria and looked up to find that a low-flying cloud had come to rest on the mountain peak, enveloping the Blanco. This night, there would be no sky observations, and no photons would break through this wet, gray blanket.
The picture above is taken looking outward from the main door to the control room of the Blanco. The telescope operator, Claudio Aguilera from La Serena, Chile, arrives for the night’s (uneventful) work.
Written by: Det. B. Nord [FNAL]
Image Credit: Det. B. Nord
A Universe of Possibilities
Over the course of billions of years, a new home is built. It will eventually house stars, planets and perhaps civilizations. The force of gravity and the conservation of momentum can transform a dense cloud of cold dust and gas into a menagerie of stars and myriad opportunities for life. The stuff of stars is the stuff of us.
This particular distant galactic home, NGC 1398, lives in the Fornax cluster of galaxies 65 million light-years away (or one billion round trips between New York City and Los Angeles). It is farther away from us each day, moving away at 1400 kilometers per second–over 3 million miles per hour. For comparison, the NASA space shuttle during launch only moves at 35,000 miles per hour.
At 135,000 light-years in diameter, NGC 1398 is just slightly larger than the galaxy we call home, the Milky Way. Like our home galaxy, it has come to burn with the light of a hundred million suns and who knows how many civilizations.
If you’d like to look for this southern hemisphere gem yourself, it lives at RA/DEC: (03 38.9, -26 20).
We close with a question: Who first wrote the now-famous equation that estimates the probability of life in the universe?
Written by: Det. B. Nord [FNAL]
Image Credit: Erin Sheldon [BNL], Martin Murphy [FNAL]
Moonrise over Tololo
In the east, peeking through a rare mountaintop tree, the Moon rises toward the Milky Way. Not too far behind, the Sun‘s rays reach over nearby mountains to at once expose the valley fog and cover the escape of distant stellar brethren into the daylight.
To the south (on the right) sits the Blanco telescope, readying for its daytime rest. Across the ridge live neighboring telescopes at the Cerro Pachon site, including world-class telescopes SOAR and GEMINI. Can you spot them on the distant ridge? (Hint: in the far right of the photo). The white lines on the ground are metal walkways that astronomers use during the night to move from one building to the other in the utter darkness; their reflectivity allows someone walking to find their way even before their eyes have fully acclimated to the darkness.
It had been a quiet night. Well, they’re all quiet nights: the loudest sound by far originates in the slow whir of motors as domes turn toward new expanses of polka-dot sky. Earlier in the evenings, the temperature drop as day changes into night causes the metal in the domes to contract slightly, and rhythmically—ka-chunk, ka-chunk, ka-chunk. It’s a reminder that we brought these machines to an alien environment, an outpost between humans and the heavens. Nestled within the dome, Blanco and the Dark Energy Camera (DECam) toil away, far more impervious to the elements and designed to be compatible with such temperature changes.
This was one of the last nights of my 10-day run at Cerro Tololo Inter-American Observatory. The moon rose earlier on nights past; when that happens, that part of the sky becomes too bright for the highly sensitive DECam. Nevertheless, we observed several patches of sky to extraordinary depth in the hopes of finding old, distant exploding stars—one of the types of objects that will help illuminate dark energy’s impact on the fate of the cosmos.
Where does moonlight originate? Hints: the moon is not a star, and it is very reflective.
Written by: Det. B. Nord [FNAL]
Image Credit: Det. B. Nord
Catching Old Light: DECam Style
A photon is born, its birthplace the heart of a star, billions of light-years away and eons ago. Its brothers and sisters headed off in all directions, but this one—this one found its way in one particular direction, toward a civilization that had just learned to command the elements enough to peek beyond the terrestrial veil. After a long, long journey this photon—this old, old light—encountered a mountain top in the Chilean desert, where it found a new home.
At the Cerro Tololo Inter-American Observatory (CTIO), an old workhorse has learned some new tricks and received some serious cyber upgrades. The Victor M. Blanco telescope (left image) was commissioned in the mid-1970s, along with its near-twin sister telescope, the Mayall, which is located in Kitt Peak, Arizona. The Blanco is a reflector-type telescope with an equatorial mount. Situated on one end of the Blanco is large mirror (left image: just right of center), which collects and redirects light toward lenses made of specially crafted glass. These lenses focus the light on a detector composed of a material that converts light into electrical signals, which are then transformed by software into images visible to the human eye. The back of the detector is shown in left image (just left of center) and the front of the detector is in the right image.
Blanco’s primary mirror is four meters in diameter, long enough for two tall people to lay across, end to end. From the primary mirror, near the base, to the detectors at the top, one could stack about 15 tall people head to toe across the 28-meter span; this is also roughly the length of a basketball court.
Every time the telescope moves to look at a new patch of sky, the motors have to shift 300 tons of glass and metal. This is the equivalent of 4300 people, 150 cars, 10 Humpback whales or 5 Brachiosaurus dinosaurs. It would take about seven Blanco telescopes to equal the weight of one space shuttle at the time of liftoff.
The telescope’s detectors are known formally as charge-coupled devices (CCDs), which are similar to photographic film, in that they are made of materials that absorb and react to light. They are also the very same kind of detector that is found in digital cameras like in your point-and-shoot, or in your mobile phone.
Over the decades of its life, the Blanco telescope has evolved, and most recently, the Blanco was retro-fitted with many new pieces of instrumentation, including new optical elements, a new shutter and other components. Critical to the mission of the Dark Energy Survey is also a new set of detectors that were developed at the Fermi National Accelerator Laboratory in Batavia, Illinois. These 62 new detectors are state-of-the-art CCDs that make up the 570 Megapixel Dark Energy Camera (DECam), which is shown in the image at the right.
DECam is not just over 50 times larger than your average point-and-shoot camera: it has unprecedented sensitivity. This camera is so sensitive it could detect light from a 100-watt light bulb as far away as the moon.
Thanks to the upgrades at the Blanco, old, travel-weary light from a billion trillion miles away, which happened to makes its way toward Earth long ago, will be welcomed with open eyes and ready minds.
Written by: Det. B. Nord, PhD [Fermi National Accelerator Laboratory]
Image Credit: Reider Hahn [Fermi National Accelerator Laboratory (Visual Media Services)]
A Family of Galaxies
In a sea of darkness, innumerable points of light come into focus. While there are some stars visible here, nearly all the red, blue and yellow objects are galaxies. In the lower left and upper right, some of the blue galaxies show off their beautiful spirals (similar to our own Milky Way). The blue color and the clear structures (bars, spiral arms, dense clouds) within these galaxies betray their basic nature: newly birthed stars emanate the blue color and the very existence of the structures means that these galaxies live in a pristine environment where gravity is the dominant force acting to clump things together. All in all, these spiral galaxies are thus relatively young.
In stark contrast, the yellower and redder galaxies have stopped forming new stars and are often referred to as ‘red and dead.’ These galaxies have endured turbulent lives: having been rocked by collisions with other galaxies, they are too hot to form stars. What’s more, all the work that gravity did to make structures within has been washed away leaving just bright cores, diffuse outskirts and elliptical shapes (and so they are named ellipticals).
Several elliptical galaxies appear clustered (just left of center of the image). These galaxies are gravitationally bound as a group or cluster. This cluster has 43 galaxies (can you find them all?), and it was one of the clusters discovered by George Abell and collaborators during the 1970’s and 80’s as part of the Southern Sky Abell Catalog (published posthumously in 1989). Amazingly, these clusters were discovered and measured with the human eye using photographic plates, rather than the electronics that the Dark Energy Survey uses, and they are part of the earliest comprehensive collection of optically observed clusters started by George Abell in 1958.
Our cluster here is Abell Catalog No. 3151 (out of over 4000), located in the Fornax Constellation. It lives just about one billion light years from Earth (actually quite close compared to the most distant clusters) and spans about five million light years from end to end.
What has dark energy done to this cluster? Galaxies within a cluster gravitate toward one another, because galaxies have mass. In contrast, dark energy stretches the fabric of space-time, upon which galaxies reside. Thus, dark energy directly opposes gravity. Dark energy can affect larger objects like clusters of galaxies, but isn’t strong enough to pull apart stars, solar systems or galaxies (where gravity is much stronger).
If gravity serves to pull massive objects (like galaxies) toward one another, then dark energy will pull them away from each other. There are millions and millions of families of galaxies across the universe, and dark energy will make them smaller.
What’s more, you’ll find small colored streaks randomly dispersed throughout the image. These come from very high-energy (fast!) cosmic rays that hit the camera’s detectors but briefly, leaving small imprints in the image. These cosmic ray streaks are just one type of artifact that have to be cleaned out of the images before cosmological questions can be asked. In future posts, we’ll discuss more about the data reduction process.
If you want to find Abell 3151 yourself, look at coordinates RA (03:38:16.61) and DEC (-28:50:32.28) in units of Degrees:Minutes:Seconds; it may be hard to see if you’re in the the Northern Hemisphere.
What other kinds of cosmological structures do you think will be affected by dark energy? Why is gravity stronger than dark energy amidst smaller structures?
Written by: Det. B. Nord, PhD [Fermi National Accelerator Laboratory]
Image Credit: DECam via Det. Erin Sheldon, PhD [Brookhaven National Laboratory]
Email us at darkenergydetectives@gmail.com if you have clues, questions or comments about anything cosmology.
Time to Meet the Neighbors!
Spiral Galaxy NGC 0895 was discovered by William Herschel in 1785. Herschel created the first maps of the Milky Way galaxy by observing and drawing the stars. Herschel also saw galaxies outside the Milky Way, but he didn’t know what they were, so he only referred to them generically as nebulae. That was the common term at the time for diffuse, extended objects – including actual nebulae, which are the gaseous remains of exploded stars.
Galaxy NGC 0895 is located in the constellation Cetus, about 110 million light years away – still a fraction (about 0.2 percent) of the observable universe. The star nearest to us, Alpha Centauri, is 4.3 light years away, and the nearest spiral galaxy, Andromeda, is 2.5 million light years away.
We can tell how many stars are forming by how blue the galaxy appears through the camera lens. Blue galaxies contain many young, newly formed stars. The golden object in the upper right is a redder galaxy, which has many more older red stars, and fewer still forming.
If you want to find NGC 0895 yourself, it is located at coordinates (RA 02 21 36.5, Dec -05 31 16).
This image was taken with the Dark Energy Camera, and shows us this galaxy in sharper detail than we have ever seen it. Check back here every Monday for another image and another story from the Dark Detectives at DES.
Welcome Home
What’s it like to look into the eye of our galaxy? Facing away from the Blanco Dome, to the north, we can see a clumpy, disc-like cloud spread across the sky. Our solar system resides in the disc of the spiral Milky Way, and when we look out to the cosmos in this direction of the sky, we’re staring into the plane of our home galaxy.
The Dark Energy Survey will observe and study hundreds of millions of galaxies, just like our Milky Way.
Only at the Cerro Tololo Inter-American Observatory in Chile (and high, dry places like it) can we see such detail in the night sky so clearly. Astronomer and amateur photographer Ricardo Demarco (and community user of the Dark Energy Camera) took this image, capturing the edge of the Milky Way with just a single 30-second exposure with his own camera.
Welcome to the Darkness
On a dark mountain-top, a car’s brake lights redden the dome of a telescope. Behind it, stars appear to drift by as the Earth slowly turns. The telescope inside that dome, however, is looking farther and deeper into the universe than those nearby bright stars. Commanded by a veritable army of astronomers, our new camera is looking for evidence of the strangest stuff in the universe, dark energy. Our mission is called the Dark Energy Survey.
What is the Dark Energy Survey? It’s a cooperative effort between about 200 scientists at more than 25 institutions around the world. Together, we’ve designed and built the Dark Energy Camera, the most powerful unclassified digital imaging device in the world, and we’ve mounted it on the 4-meter Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile.
Over the next five years, we’re going to use this camera to measure hundreds of millions of galaxies and thousands of supernovae in an effort to understand dark energy. That’s the name given to the mysterious substance that is causing our universe to expand faster and faster. We’re going to map a portion of the southern sky in unprecedented detail in order to study this accelerating expansion.
And along the way, we’re going to take some beautiful pictures, and we’re going to share them with you here every week.
We’ll start with this composite photo of the dome that houses the Blanco telescope. This image was made by taking multiple 30-second exposures over several hours, then combining all the images of the sky with a single image of the dome. The red glow was caused by brake lights on the road in front of the dome. The center of the arcs of light in the sky is the South Pole – it’s fixed in space, and the Earth rotates around it.
We can also see some multi-colored dashed arcs of light, moving in different directions. Those were caused by airplanes.
Dark Energy Detectives 