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.]
We are swept up in a cosmic merry-go-round.
Earth spins relative to the sky – about one revolution every 24 hours.
After twilight, our nearest star, the Sun removes its warm blanket of light, revealing the dancing lights overhead: collections of aeons-old galaxies and constellations of distant stars fill the night sky. For some precious hours, we have exquisite access to these pinpricks and smudges of light that have always swirled overhead – until we bask again in the Sun’s rays. During the day, all blinking tapestry is still above us, but the Sun washes out any hope of seeing it. Again, after dusk, familiar patterns fill the sky, as the dancers return like clockwork to their positions on the celestial stage.
Our entire solar system resides in a galaxy, the Milky Way. The Galaxy’s structure includes spiral arms and a disk of stars and gas: our pale blue dot, tethered to the Sun, is nestled in the suburbs, halfway to the edge of the Galactic disk. As we turn from day to night to day, the Galaxy itself also spins (over much longer periods than Earth’s day).
During the course of our daily/nightly sweep of the heavens, just as the stars and galaxies move across our sky, so does the disk of Milky Way. When we look up from the dark mountain tops of Cerro Pachon, we look into the plane of the Milky Way, into the heart of our Galaxy.
In the video above, the camera rotates from East to West through South – taking a picture every 30 seconds over the course of the night. Earth’s axis goes through the South pole, so we see the sky spin about that point: one side of the Milky Way sets, and by 1am on this October night, another side begins to rise.
Good night, and keep looking up,
Det. B. Nord
For the last week, detectives from the Dark Energy Survey have been coordinating across four continents to bring to light more evidence of how the fabric of spacetime is stretching and evolving.
In Sussex, England, over 100 detectives met to discuss the current state and the future of the Survey that is conducted at the Blanco telescope, located at Cerro Tololo in Chile. At this semi-annual collaboration meeting (with a new venue each time), we continued to strategize analyses for the many probes of spacetime evolution and dark energy: as I write, several early results are being prepared for publication.
At Cerro Tololo, a team of observers operated the Dark Energy Camera (DECam) on the Blanco telescope, as we make our way through the second season of observing for the Survey. Each season goes August through February, during the Chilean summer.
The Anglo-Australian Telescope at Siding Spring Observatory in Australia is home to the OzDES Survey – long-term project for obtaining highly precise distance measurements of objects discovered by DES, such as supernovae and galaxy clusters. These “follow-up” measurements will be very important evidence in pinning down the culprit for dark energy.
At Cerro Pachon, just east of Cerro Tololo, another team of two agents began to search for evidence of highly warped space in the distant cosmos, using the Gemini (South) Telescope (@GeminiObs). We spent six nights working to measure highly accurate distances of strong gravitational lensing systems. These systems are galaxies or groups of galaxies that are massive enough to significantly distort the fabric of space-time. Space and time are so warped that the light rays from celestial objects – like galaxies and quasars – behind these massive galaxies become bent. The resulting images in DECam become stretched or even multiplied – just like an optical lens. In future case reports, we’ll expand on this phenomenon in more detail.
All the while, supercomputers the National Center for Supercomputing Applications (NCSA) are processing the data from DECam each night, turning raw images into refined data – ready for analysis by the science teams.
The image above doesn’t display any obvious strong lenses, but it is an example of the exquisite lines of evidence that DES continues to accumulate each night.
Here are positions of some of the galaxies above. What information can you find about them? There are several electronic forensic tools to assist your investigation (for example, http://ned.ipac.caltech.edu/forms/nearposn.html; take care to enter the positions with the correct formatting, as they are below). Tweet your findings to our agents at @darkenergdetec, and we can compare case notes.
RA: 304.3226d, Dec: -52.7966d
RA: 304.2665d, Dec: -52.6728d
RA: 304.0723d, Dec: -52.7044d
Good night, and keep looking up,
Det. B. Nord
Det. M. Murphy [image processing]
Across North America, as the transition toward winter begins, we see symptoms in the changing colors of tree leaves. The lively green hue of summer gives way to yellows, oranges, reds and purples. Living cells inside the leaves have instructions for how to react to cooler and cooler environments: this reaction reduces the production of the green pigment, chlorophyll, allowing other colors (caused by the pigments of the carotenoids and anthocyanins) to dominate. When spring returns, so do leaves, newly filled with oxygen-producing chlorophyll.
Year after year, we watch the cycle of death and rebirth in the life-giving foliage around us.
But what if we were insects? What if, like the mayfly, we lived for only a day or two? Would we have any way of understanding the immense tapestry evolving around us? Imagine for one day on Earth, looking at leaves all over the globe – in different environments and in various states of health and age. With just this one day to create a coherent picture, could we piece together the clues of color, environment and the internal workings?
This is the challenge we face in understanding the life-cycle of galaxies, the leaves on our cosmic tree of matter and light. To these celestial objects, we are indeed the mayfly, living for only a blink of an eye in cosmic time.
Consider the cornucopia of dusty swirls in the image above, their colors spanning the entire visible rainbow and beyond. Each puff of light contains billions of stars. Through our telescopes, images and spectrographs, we learn about the kinds of chemicals, of matter that reside within galaxies. Through an understanding of physics, we link this information to the possible physical processes, from gravity to quantum mechanics.
Similar to that of tree leaves, the colors of galaxies are the result of the chemical constituents, and they reflect their ages. Blue galaxies, still young, are cold enough to be forming stars, because young stars and the gas enshrouding them release bluer light to the cosmos. Red galaxies have had their star-formation extinguished: their gases are too warm for the force gravity to collapse them into energy-generating balls of fusion. These ‘red and dead’ galaxies represent the end of the galactic life-cycle.
While we have ways of peering inside galaxies to reveal some of their guts, we still have no way to watch an entire galaxy come into being, much less live out a full life. Each galaxy represents its own tributary of time, its own puzzle piece in the delta of the cosmic web.
Det. B. Nord
Image: Dark Energy Camera [Edited and logged by Det. M. Murphy]
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
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
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.