July 1, 2013
Dark Energy Survey Will Look For Supernovae
John P. Mills, Ph.D. for redOrbit.com - Your Universe Online
The greatest cosmological puzzle of the 21st century continues to be to measure, characterize and understand the source of dark energy, the apparent force that is driving the accelerating expansion of the Universe. One of the problems is that in order to make accurate measurements of the expansion rate, astronomers must measure the motions of distant galaxies, some near the very edge of the known Universe.At such great distances, these objects appear very dim and are, consequently, difficult to study. To aid scientists in their search, they often look for supernova explosions occurring in these galaxies. For one, these events produce a momentary brightness that makes the galaxies easier to "see." But more than that, supernovae explode in a predictable way, and their measured brightness can be used to make rather accurate distance measurements to these galaxies.
In order to try and better understand dark energy, astronomers are now preparing to launch the most comprehensive search for distant supernovae in history. Being launched in August, the Dark Energy Survey (DES) will undertake a five-year mission to chronicle the locations and motions of supernovae across the cosmos.
"Thanks to the extreme sensitivity of the camera and to the large area of sky that can be imaged through the telescope at once (about 15 times the size of the full moon), we expect DES to find more supernovae than any previous experiment. During the verification phase, we have already identified at least 200 good candidates," said Dr. Chris D'Andrea, a researcher at the University of Portsmouth's Institute of Cosmology and Gravitation.
This method for studying dark energy is not new. In fact, the original work on dark energy in the mid-90s by Nobel Prize winning physicsts Saul Perlmutter and Brian Schmidt, used supernovae data to unmask the dark acceleration. But while their work centered around a few dozen events, the DES will seek out more than 3,500, adding a whole other level of sensitivity to the search.
"Traditionally, astronomers have identified supernovae by analyzing the spectrum of light from candidates," according to D'Andrea. "Because DES will give us so many candidates, we already have hundreds just from the commissioning phase. We don't have the resources to do this for each individual candidate supernova. We need to use other techniques to confirm which of the objects we observe really are exploding stars."
By monitoring the galaxies in which the candidate supernova events have occurred, researchers can gather information about the motion and brightness of the galaxy as a whole. Then, the team can use information about the supernova color and brightness to assess how likely the source is really a supernova.
"DES is a long-term survey. We may not know whether some of our candidates are 'real' supernovae until the end of the project. However, in collaboration with Australian researchers, our team has recently been awarded 100 nights of time on a telescope in Australia over the next five years. The Anglo-Australian Telescope has the ability to take spectra of nearly 400 galaxies at the same time. With the first of these nights scheduled for September, it won't be that long before we can start to accurately classify the supernovae candidates discovered in DES," said D'Andrea.