11 September 2013

Dark Energy Survey will spy on supernovae to explain universal expansion

It was revolutionary enough when we found out that the universe was expanding — that put an end to the static universe theory held by everyone from Aristotle to Einstein. It at least fit with the existing theory of the Big Bang though, as the material of the universe continued to hurtle away from the point of its initial expulsion. In the 1990s, several observations made the situation far more bewildering, proving that the universe isn’t just expanding, but expanding ever faster. Suddenly existential fears about the universe collapsing back down in a Big Crunch turned into equally existential fears about the universe blowing apart into diffuse, particulate nothingness. Worse: this time, we had no model to explain the findings.

Eventually physicists began to see, if not the cause of this acceleration, then at least what such a cause might look like. Like positing a Higgs boson purely because such a particle would be convenient if it did exist, physicists invented two new stand-in concepts in physics: Dark matter, and dark energy. On August 31, after more than a decade of planning and technical development, the Dark Energy Survey (DES) began its attempt to characterize the latter of these two concepts, and with it the nature of the universe itself. Dark energy can currently only be defined by reverse-engineering its observable effects; the DES will let researchers greatly refine those estimates.

A prototype of the Dark Energy Camera, at Fermilab.

They don’t call it dark energy for nothing, however; even viewing the effects of dark energy is difficult in the extreme, and this dedicated survey has had to invent new technology for the purpose. The international team has commissioned parts from five different countries in assembling the world’s most sensitive digital camera for their particular needs. The 570-megapixel Dark Energy Camera (DECam) uses five lenses to focus light from the red and near-infrared portion of the light spectrum onto its 62 imaging CCDs. It’s the world’s most advanced tool for this job, able to see up to 8 billion light years away. Operating from the Victor M. Blanco 4-meter telescope in Chile, it will glean more from the red portion of the spectrum than ever before.

Particularly, the survey is looking for Type Ia Supernovae, which only occur in binary systems. The intensity of these explosions can tell the astronomers the distance to the supernovae, since these events are considered “standard candles” with a reliable, uniform brightness based on their distance. The second piece to the puzzle lies on the red end of the visible light spectrum, and that’s where DECam truly shines. If the universe is expanding more and more quickly, the light incoming from these supernovae should be red-shifted — that is, the light should appear to be closer to the red end of the spectrum than normal. The more red-shifted an object is, the faster it is moving away.
The Victor M. Blanco Telescope in Chile.


Since light moves at a uniform rate, the more distant an observed event, the longer ago it occurred. In a general sense, if universal expansion is accelerating, then the closer (more recent) supernovae should exhibit more red shifting than the farther (more ancient) ones, on average. By compiling this data, the researchers will be able to define the properties of dark energy more accurately than ever before. Dark energy could be very different than we currently imagine, or it could even be several different quantities working in tandem. It’s impossible to know without a better understanding of its impact on the universe.

The Dark Energy Survey isn’t just looking out for supernovae, however — that’s just one of its four prongs of attack. By measuring Baryon Acoustic Oscillations in conjunction with the distribution of galaxy clusters and the bending of light (lensing), the Dark Energy Survey will give us unprecedented insight into how our universe is evolving over time, and why. It will operate over the next five years, taking snapshots of about an eighth of the sky and observing an estimated 4000 new supernovae events, along with 300 million galaxies and 100,000 galaxy clusters.

Let’s hope it’s enough.

Now read: Earth and Moon photographed from 900 million miles away, from the shadow of Saturn


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