January 23, 2004  


Astrophysics Program Investigates Dark Matter

By Linda DuShane White

Steve Kahn’s primary focus as Deputy Director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) is to develop major new programs. "As is essential for scientific programs at SLAC, two programs have been presented to and approved by the Experimental Program Advisory Committee (EPAC) in November 2003. So we have the green light to go forward," explains Kahn. These two programs are cornerstone elements of the new Kavli experimental program. Both are in the early stages, and both involve relatively substantial programs in experimental cosmology performed at SLAC. "Both of these projects are very visible national projects that have a prominent role in U.S. programs," Kahn added.

Image of the LSST facility, one of two major approved programs in experimental cosmology. (Image courtesy of G. Muller/C. Claver, NOAO/AURA/NSF)

The first of these programs is the Joint Dark Energy Mission (JDEM), an acronym that was created by the program coordinators—NASA and DOE. Originally initiated by LBNL, SLAC is now collaborating on JDEM. Some readers may know this program by its former name, the Supernova/Acceleration Probe (SNAP) Mission.

According to Kahn, the mission is designed to explore the physics of dark energy, one of the great mysteries in cosmology that have come up in the last five years.

Universe Expansion

JDEM is a space-based experiment designed to measure the expansion history of the Universe, motivated by the discovery that the expansion is accelerating.

"The expansion of the Universe implies the existence of an energy field which effectively gains energy as the Universe expands," Kahn notes. "We have no current physics idea about where this comes from." As always in science, questions lead to more questions. Other scientific aspects of JDEM include looking at gravitational lensing. There will be an optical telescope in space and what is basically a large camera that takes pictures of the sky.

SLAC will provide most of the electronics that make the camera work, as well as the flight software and flight computer that will control the whole unit. Currently there are only a few people working on JDEM, but Kahn predicts that 20 people will eventually work on this significant project. The estimated launch date is 2014.

Surveying the Sky

Kahn describes in fascinating detail the second project—the Large Synoptic Survey Telescope (LSST)—another way of learning about the intriguing field of dark energy and dark matter. LSST is a very large ground-based telescope that can take pictures of the sky over a very wide field, and is a joint collaboration of NSF and DOE. LSST will survey the entire sky every few days down to very faint levels.

"The science here is to use the distortion of background galaxies due to gravitational lensing," said Kahn. There is dark matter in the Universe and the light from distant galaxies propagates to us. It gets slightly bent by the intervening gravitational matter which you can see by looking for correlated distortions in the sky. Those distortions will tell you about the dark matter and the clumping of the dark matter. How concentrated it is tells us about the expansion history of the Universe.

The entire camera will be built here at SLAC—and what a camera it will be. Kahn explains, "This is large—bigger than any camera built before in astronomical work—and it will be almost comparable in size and complexity to the inner regions of an accelerator detector. So that’s why a lot of the SLAC experience in building detectors for high energy physics is applicable to this project." Five or six people are now working on this project, and it will probably end up with 15-20 people. SLAC is the lead DOE laboratory on this project with collaborators at LLNL and at BNL, as well as university based high energy physics groups.

This incredible camera will take deep, wide pictures of the sky every ten seconds, thereby covering the entire sky every few days. Befitting such an amazing invention, "We’ve been calling it celestial cinematography," Kahn says.

We are indeed fortunate at SLAC to have KIPAC provide the opportunity to delve deeply into mankind’s age-old questions about the Universe via JDEM and LSST. The resultant deeper understanding of dark energy, dark matter and the Universe itself will prove not only fascinating, but enchanting, to scientists and non-scientists alike.

For more information see: http://www-group.slac.stanford.edu/kipac/


The Stanford Linear Accelerator Center is managed by Stanford University for the US Department of Energy

Last update Friday January 30, 2004 by Kathy B