SLAC Today is
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In this issue:
High-energy Electrons Could Come from Pulsars—or Dark Matter
A 35th Anniversary for SLAC X-ray Science
Colloquium Next Monday: The Compact Light Source
Around SLAC: Celebrating LCLS
Monday - May 4, 2009 |
High-energy Electrons Could Come from Pulsars—or Dark MatterSomething in our galactic neighborhood seems to be producing large numbers of high-energy electrons, according to new data gathered by the Fermi Gamma-ray Space Telescope. The electrons could be coming from nearby pulsars—or they could be a longed-for signal of dark matter, the elusive, invisible material thought to make up nearly a quarter of the universe. FGST's Large Area Telescope, a collaboration between NASA, the U.S. Department of Energy and multiple international partners, has been scanning the skies for gamma rays and particles since its launch last summer. The LAT, which was partially constructed and assembled at SLAC, measured an unexpectedly high number of electrons with energies between 100 billion and one trillion electronvolts. This result is not likely if high-energy particles—also known as cosmic rays—are coming only from distant parts of the galaxy. "If these particles were emitted far away, they'd have lost a lot of their energy by the time they reached us," said LAT collaborator Luca Baldini of the Istituto Nazionale di Fisica Nucleare in Pisa, Italy. When combined with other recent results, the LAT finding provides compelling evidence that something close by—probably less than 6,000 light years away—is churning out high-energy particles. The European satellite PAMELA, for example, last fall reported detecting surprisingly large quantities of high-energy positrons, the antimatter counterparts of electrons. "Between the PAMELA results and our results, it's very hard to construct a conventional galactic cosmic-ray model" explaining this number of high-energy particles, said SLAC Professor Elliott Bloom, who works on the LAT project. "You need relatively local sources of positrons and electrons." Read more... LAT collaborator Luca Latronico, from the University of Pisa in Italy, will discuss the team's results in a seminar at Kavli Auditorium on Wednesday, May 6, from 12:30 to 1:30 p.m. Also on Wednesday, SLAC physicist Philip Schuster will host a seminar and discussion on the LAT findings, 3:00–4:30 p.m. in Kavli Auditorium. A 35th Anniversary for SLAC X-ray ScienceThirty-five years ago this month, the Stanford Synchrotron Radiation Project—the precursor to today's Stanford Synchrotron Radiation Lightsource—began operations. The SLAC archives note that SSRP was the world's first synchrotron radiation hard X-ray lightsource based on an electron storage ring. SSRP science launched with five experimental stations sharing SLAC's first X-ray beamline. For more about the SSRP, see the SLAC Archives and History Office SSRP timeline and photo gallery. Colloquium Next Monday:
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