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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

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Light-years Away, Right at Home

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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.

Today, there’s an announcement about the beginning of Season 2, along with a spate of videos and images about the team of detectives, the location and the machine we’ve built.

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New Beginnings: Our Darkness (Re)Lit

DES0500-6205_cut_MJM.Nebulosity.3.3.960pxWhat 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

Video

DECam Tracks Near-Earth Asteroid

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

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Beyond the Veil, but not Beyond Reach

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

Video

One Star Sets, Others Rise

The first season of the Dark Energy Survey is now drawing to a close. For another few weeks, we will continue to watch the sky from the summery Southern Hemisphere. After that, others in the astronomy community will take the reins of the Dark Energy Camera (DECam) until September.

Early in the season, the clouds (and occasionally rain) interrupted this work. For example, in October of 2013, late-evening skies of plum-golden hue gave us the sunsets you see in today’s picture. Even though there were cloudy nights early in the season, this was anticipated. We’re using basic climate and weather models to plan our survey, so we can still observe fruitfully when visibility isn’t the best. Moreover, we can use the data from this past year to improve our survey strategy for the coming four years.

However, the rest of the season has been great, with many nights of very little air turbulence in the atmosphere, meaning we captured very clear images. Astronomers talk about this using the term, “seeing,” which is measured in “arcseconds.” The lower the seeing, the clearer and crisper the images. At the Cerro Tololo Inter-american Observatory, typical values are near one arc-second.

Right now, our squads are sifting through and preparing these images for science, and preparing them to share with you.

In less than a month, the sun will rise on our first season, but the long nights of work will continue.

 

Det. B. Nord

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CSI: Early Universe

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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]

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