Revolution
When is the last time you watched the sky revolve around us?
Earth rotates on its axis at 1,000 miles per hour (1600 kilometers per hour). At the same time, it flies around the sun at 67,000 m/h (110,000 km/h). And the Sun, with all its planets and rocks and dust in tow, makes its way around the center of the Galaxy, our Milky Way, at 520,000 m/h (830,000 km/h). And then, the Milky Way itself is hurtling toward the nearby Andromeda galaxy at 250,000 m/h (400,000 km/h).
The fastest space craft (and fastest man-made object in history), Juno, will slingshot around Earth on its way to Jupiter, eventually reaching a speed of 165,000 m/h. The NASA space shuttle reaches speeds of 17,000 m/h (27,000 km/h).
The average human walking speed is 3.1 m/h (5.0 km/h).
Though we sit in this coordinated maelstrom, we can still understand all of space and time on the largest scales. But, to do so, we must consider it statistically, on the whole, at great breadth and as a collection – not merely the sum of disconnected parts or separate events.
All across the universe, there are supernovae – exploding stars that blink in a cataclysmic, cosmically infinitesimal moment. Quasars are small regions that surround the supermassive black holes at the centers of galaxies that flash on and off on the timescales of hours to months. Each galaxy in the universe is creating some dimple in space-time due to its mass. Imagine a vast expanse of sand dunes: all light passing by these galaxies must traverse through it, resulting in distorted images by the time they get to us.
These are just some of the events that go on constantly around us, without regard for our existence, as we spin round and round, imagining a static quilt of stars turning about us. And they are just some of the celestial targets that will tell us more about how fast the universe is expanding.
To better understand these events, and the acceleration of spacetime, we wait for the targets to be at a place in the sky when we can see them – when the sun is down and this part of Earth is pointed in their direction. Our targets come from a large swath of sky, one-eighth of the celestial sphere. And across this expanse, we will obtain a uniform sample of targets. The uniformity – homogeneity or constancy – is crucial: we must observe all galaxies brighter than a certain amount, and within a certain distance to have a clean, uniform sample. Otherwise, variations in that information could be misconstrued, or at best they could muddy our measurement of dark energy.
Building the collection starts with amassing a set of deep images of the sky: these are but snapshots of long-gone eons, and they are the first step in our process of discovery. From the images, we distill vast catalogs of celestial bodies – galaxies, stars, motes and seas of hot gas and dust – an accounting of what the universe has so far created. This catalog can be further distilled when studied as a whole. The final concentrate is a small set of numbers that summarizes the fate of our universe: a measurement of the strength of dark energy.
Our spaceship Earth is a pebble in the swirling cosmic sea around us. We watch it as if we are separate, sometimes forgetting we come from it. As we look up from within our snowglobe on a mountaintop in the Chilean Andes, it becomes easier to remember that we are a conduit between the finite and the infinite.
Good night, and keep looking up.
Det. B. Nord
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.
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]
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
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 