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