Sometimes, you can feel it coming in the air of the night.
Weather is fickle, but when a night of observing begins, we usually know how it will go. The first part of this season was often rainy and gray. The last several weeks, however, have allowed for new records in precision the precision of DECam data.
On Nov 11 and Nov 18, 2014, the Dark Energy Survey took exquisite data of all of our supernova fields – the regions of sky selected specifically to look for exploding stars. It was clearer than anything we’d seen previously. The video above is from a night early in this season, when the weather was also extremely good (but only for a few days). It is a view, from inside the dome, of DECam and the Blanco Telescope scanning the sky over the course of one night in August, 2014.
After a few nights of clouds or rain, it usually takes another night or two for the atmospheric turbulence to die down. This turbulence deflects light as it comes through the layers of Earth’s atmosphere, effectively blurring an image. But when this turmoil is no longer there, the conditions can be pristine.
Sometimes, you can feel it coming in the air of the night. It’s the final moment for so much starlight.
We are here to see what it did, see it with DECam’s 570 million eyes. DECam’s been waiting for this moment all of its life. Now we know where you’ve been, traversing the dark night skies.
The light of distant galaxies and stars has been waiting for this moment all that time.
Now forever, we remember where the light has been, how could we forget. When our detectors capture it, it’s the first time, the last time, we’ve ever met. We know the reason you kept your silence up. When it was cloudy, how could we know. When it’s clear, the signal still grows, the universe no longer a stranger to you and me.
Sometimes, you can feel it in the air of the night.
Det. B. Nord
[Hat tip to Phil Collins.]
En el hemisferio norte, a medida que comienza la transición hacia el invierno, vemos los síntomas de este proceso en los cambiantes colores de las hojas. El animado tono verde del verano da paso a los amarillos, naranjas, rojos y morados del otoño. Las células vivas de las hojas tienen instrucciones sobre cómo reaccionar a ambientes más frescos y fríos. Esta reacción reduce la producción del pigmento verde, la clorofila, lo que permite que otros colores (creados por los pigmentos de los carotenoides y antocianinas ) prevalezcan. Cuando regrese la primavera, también lo harán las hojas, de nuevo con abundante clorofila productora de oxígeno. Año tras año, vemos este ciclo de muerte y renacimiento en el follaje a nuestro alrededor .
Pero… ¿y si fuéramos insectos? ¿Qué pasaría si, al igual que la moscas, viviéramos durante sólo uno o dos días? ¿Tendríamos alguna forma de entender el inmenso tapiz en evolución que nos rodea? Imagina un único día en la Tierra, observando las hojas por todo el mundo – en diferentes ambientes y en diversos estados de salud y edad. Con sólo este día para crear una imagen coherente, ¿seríamos capaces de reconstruir el funcionamiento interno de este ciclo con estas pistas?
Este es el reto al que nos enfrentamos en la comprensión del ciclo de vida de las galaxias, las hojas de nuestro árbol cósmico de materia y luz. Para estos objetos celestes, de hecho somos como las moscas, que sólo viven durante un abrir y cerrar de ojos en escalas cósmicas de tiempo.
Observa la multitud de remolinos de polvo en la imagen de arriba. Sus colores abarcan todo el arco iris visible y más allá. Cada mancha de luz contiene miles de millones de estrellas. A través de nuestros telescopios, imágenes y espectrógrafos, aprendemos sobre los tipos de productos químicos de la materia que reside dentro de las galaxias. A través de la comprensión de la gravedad y la mecánica cuántica, vinculamos esta información a los posibles procesos físicos que están teniendo lugar.
De manera análoga a las hojas del árbol, los colores de las galaxias son el resultado de sus componentes químicos y reflejan su edad. Las galaxias azules, todavía jovenes, son lo suficientemente frías para estar todavía formando estrellas, porque sus estrellas jóvenes y el gas que las envuelve liberan luz azul al cosmos. Las galaxias rojas han visto como su periodo de formación estelar se extinguía: su gas ahora es demasiado caliente para que fuerza de la gravedad pueda colapsarlas en ardientes esferas. Estas galaxias rojas y muertas representan el final del ciclo de vida galáctico .
Si bien tenemos formas de observar las entrañas de las galaxias, aún no existe la manera de observar cómo se forma una galaxia, y mucho menos ver su vida entera. Cada una representa su propio afluente del río del tiempo, su propio pedazo del rompecabezas en la delta de la red cósmica .
Det. B. Nord
Imagen: Dark Energy Camera [Edited and logged by Det. M. Murphy]
Traducción: Nacho Sevilla
As the Milky Way sets, light from nearby villages and mining towns turns the stream of clouds overhead into a rippling river of fool’s gold. On this night in October of 2013, during the first season of observations of the Dark Energy Survey, we pumped caffeine into our bodies to stay awake, to keep ready for when the conditions would change. Every field we can observe, every galaxy we can capture will make a contribution to the greater measurement of their vast patterns – patterns distorted (or created) by a dark energy.
One hundred years ago, an American astronomer by the name of Vesto Slipher became the first to measure streams of galaxies in our local neighborhood. Slipher used the 24-inch telescope at Lowell Observatory to measure velocities of spiral nebulae (i.e., galaxies), through a method known as “spectroscopy.” Most of the galaxies that Slipher measured are receding from the Milky Way, rather than moving toward it – the first indication of cosmic expansion.
This result laid the groundwork for the definitive discovery of the expanding universe. Unfortunately, Edwin Hubble of Mount Wilson is most often accredited with this finding. Hubble measured distances via Cepheid Variables to distant nebulae and then correlated them with Slipher’s velocity (redshift) data to create the famous distance-velocity plot for his 1929 paper.
Hubble provided no citation of Slipher’s work.
Slipher is the first to measure Doppler Shifts (velocities) of galaxies, to show that spiral galaxies rotate, and to detect that collections of stars and dust are actually nebulae outside our own Milky Way.
Let us remember Vesto Slipher – among modern cosmology’s most influential unsung heroes.
Det. B. Nord
After a great journey, a long-hidden member of our solar system has returned. Not since the 9th century, when Charlemagne ruled as Emperor of the Holy Roman Empire and Chinese culture flourished under the Tang Dynasty, has this small icy world re-entered the realm of the outer planets.
This distant wanderer is among first of its kind discovered with data from the Dark Energy Survey (DES). Now officially known as 2013 TV158, it first came into view on October 14, 2013, and has been observed several dozen more times over the following 10 months as it slowly traces the cosmic path laid out for it by Newton’s law of gravitation. We see this small object move in the animation to the left, comprised of a pair of images taken two hours apart in August, 2014.
It takes almost 1200 years for 2013 TV158 to orbit the sun, and it is probably a few hundred kilometers across – about the length of the Grand Canyon.
In eight more years, it will make its closest approach to the sun – still a billion kilometers beyond Neptune. At this distance, the sun would shine with less than a tenth of a percent of its brightness here on earth, and would appear no larger than a dime seen from a hundred feet away.
That’s what high noon looks like on 2013 TV158.
Then it will begin its six-century outbound journey, slowly fading from the view of even the most powerful telescopes, eventually reaching a distance of nearly 30 billion kilometers before pirouetting toward home again sometime in the 27th century.
This object is just one of countless tiny worlds that inhabit the frozen outer region of the solar system called the Kuiper Belt, an expanse 20 times as wide and many times more massive than the asteroid belt between Mars and Jupiter. The dwarf planet Pluto also calls the Kuiper Belt its home. The orbits of Jupiter, Pluto and 2013 TV158 around the sun can be seen in the image to the lower right.
Scientists believe that these Kuiper Belt Objects, or KBOs, are relics from the formation of the solar system, cosmic leftovers that never merged into one of the larger planets. By studying them, we can gain a better understanding of the processes that gave birth to the solar system 4.5 billion years ago.
Because they are so distant and faint, KBOs are extremely difficult to detect. The first KBO, Pluto, was discovered in 1930. Sixty-two years would pass before astronomers found the next one. Astronomers have identified well over half a million objects in the main asteroid belt between Mars and Jupiter. To date, we know of only about 1500 KBOs.
DES is designed to peer far beyond our galaxy, to find millions of galaxies and thousands of supernovae, but it can also do much more. DES records images of ten specific patches of the sky each week between August and February. These images are a perfect hunting ground for KBOs, which move slowly enough that they can stay in the same field of view for weeks or even months. This allows us to look for objects that appear in different places on different nights, and eventually track the orbit over many nights of observations.
So far we’ve searched less than one percent of the DES survey area for new KBOs. Who knows what other distant new worlds will wander into view?
Det. D. Gerdes
As the Galaxy sets behind the Blanco telescope, our home away from home, we are reminded of where we really are. Earth resides in a mere village of planets, one of many in a city of stars – our Milky Way galaxy – which, as these detectives see it, is our true home.
But it is the distant stars and galaxies, just like those we call home, that betray patterns in our cosmos.
We operate in the dark of night to find as many as we can, as carefully as we can. We track locations, movements, interactions, explosions and lifetimes of millions of individuals. Only these clues in aggregate (for the most part), will lead us down a starlit path to an understanding of our universe’s greatest tug of war: that which is between the pull of gravity and the accelerating expansion of dark energy.
The detectives have gone back to work for Season 2 of observing and combing the logs of photons as they stream into the trap we’ve set, the Dark Energy Camera (DECam). In the coming months, we’re turning these streams into nuggets of knowledge, the first puzzle pieces to be revealed by the Dark Energy Survey (@theDESurvey).
And ultimately this knowledge brings us back home, to understanding our place in the cosmos.
I’m here now at the Blanco, writing this as we prepare for our third night of observations and tracking in Season 2 of DES, with bags under our eyes, coffee mugs in hand, watching the fires in the sky.
Det. B. Nord (@briandnord)
If you run into us where the electrons roam (FB, Twitter, Reddit, etc.), don’t be afraid of the dark – get in touch. We’ll report every two weeks (and occasionally more), and we’ll have more detectives and more ways to tell the stories.
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
In the early evening of February 3rd, 2014, the DES team received an urgent request for optical imaging of a Near Earth Object (NEO) on a “potentially hazardous orbit.” This asteroid had first been spotted by the NEOWISE (NEO Wide-field Infrared Survey Explorer) team. However, they had been unable to pin down its orbit. Additionally, poor weather in Hawaii and Arizona had stymied all other attempts to image this object. To make matters even worse, the asteroid was rapidly moving towards lower solar elongations which would bring it in line with the Sun and make later observations impossible.
Luckily, the Dark Energy Survey (DES) was on the scene as humanity’s best, last, and only line of defense. Cerro Tololo was enjoying some of the finest weather Chile has to offer, and DECam’s large field of view makes it an excellent instrument for tracking down errant asteroids. Soon after sunset, the Blanco 4m telescope swung towards the best guess for the asteroid’s position and DECam took five images, dithering slightly to make sure the asteroid couldn’t slip through the gaps between CCDs, DECam’s digital imaging chips.
After rapid processing, the DECam images revealed a new Apollo-class asteroid, 2014 BE63. The NEOWISE team confirmed that 2014 BE63 will cross the Earth’s orbit; however, the closest approach to Earth itself will be at a safe distance of 18 million miles.
We dark energy detectives can rest easy knowing that, in the words of Steve Kent [FNAL], “2014 BE63 poses no threat to DES observations (and no threat to Earth).
Written by Detective Alex Drlica-Wagner [DES, FNAL]
Video by Alex Drlica-Wagner
When I awake each afternoon during an observing mission at the Cerro Tolo Inter-American Observatory (CTIO), I have one priority. Before I eat, before I check e-mail, before I even stretch, I step out the door and look to the west: are our skies clear? Clouds can cast a shroud over a night’s observing program for the Dark Energy Survey (DES), which is now in full swing, each night gathering a terabyte of clues to dark energy. If our view is blocked by clouds, if we’re not taking data and peering into the deep black, we’re missing precious opportunities to observe space-time’s expansion.
To mitigate this, the Dark Energy Survey has developed another tool to pierce the veil of Earth’s atmosphere: the Radiometric All Sky Infrared Camera, or RASICAM.
The video above shows RASICAM closed during the day and then open after sun-down. RASICAM sees the entire sky in the infrared wavelengths, where our eyes are blind, but the clouds show up clearly. DES scientists and engineers at the Stanford Linear Accelerator Center (SLAC) National Laboratory designed and constructed this all-seeing eye on the infrared sky, and it’s been operational at CTIO since 2011 (http://today.slac.stanford.edu/feature/2010/rasicam.asp). In future posts, we’ll look at the sky from RASICAM’s point of view.
RASICAM is critical to DES operations. We use this camera to help inform us about how many clouds are in the sky, as well as where they are. We can then adjust our observing strategy and better analyze the image data. The instrument is brought to us by Rafe Schindler, Peter Lewis and Howard Rogers. Data analyses and maintenance are performed regularly by Kevin Reil, Dave Burke, Peter Lewis and Zhang Zhang.
Occasionally, clouds may appear or rain may fall, but dark energy cannot hide from us.
Det. B. Nord
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.
Written by: Det. B. Nord [FNAL]
Image by: Det.’s Nikolay Kuropatkin and Martin Murphy [FNAL]
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]
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]
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]
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.
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]
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]
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.)
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.
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]
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.
It is early in the life of the universe. Cold clumps of inanimate matter are randomly distributed throughout the cosmos. In this randomness, some places have more matter, more stuff, than other places: some regions are denser than others. Over time – millions and billions of years – the force of gravity causes these dense clumps to accumulate more and more matter, often taking from the already-emptier places. Essentially, when it comes to the growth of structure (from planets to galaxies and all the way up to the largest scales of the universe), the rich get richer, and the poor get poorer.
Fast forward to the present and we can see the results of this evolution.
Some galaxies were born in very rich environments; and while they started blue, today they are red. These galaxies, like some we’ve seen in earlier posts, become red because of all the massive stuff running around nearby them, disrupting the formation of their stars. These red galaxies have come to live in clusters.
Other galaxies that don’t live near a lot of stuff don’t have that problem. They live in the field, and they can still give birth to stars, because other galaxies aren’t whizzing by them. These galaxies will remain blue for a long, long time as they drift along in their lonely, relatively empty piece of the universe.
NGC 1090 is one such field galaxy that lives 135 million light-years from Earth – equivalent to about 1.5 million billion round trips between Earth and the Moon. It resides in the Cetus constellation and lies near a group of galaxies, M77. However, NGC 1090 is not gravitationally bound to M77: it is completely unassociated; it is alone.
In the far, far, far future, dark energy may continue to pull objects farther and farther away from each other, and it may do so faster and faster – despite gravity’s attractive force. Eventually, all galaxies could live in their own lonely regions of the universe.
If you’d like to track down the lonely NGC 1090 yourself, it sits on the celestial sphere at RA (02h 46m 33.9s) and DEC (-00° 14′ 49″)
Written by: Det. B. Nord [FNAL]
Image credit: Det. M. Murphy [FNAL], Det. N. Kuropatkin [FNAL]
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
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?
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.
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]
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