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Gamma rays streaming from stellar explosions stump astronomers

Novas may be a previously unrecognized source of high-energy flashes

4:01pm, August 4, 2014

STRANGE FLASHES  The Fermi satellite has discovered four instances of gamma rays coming from novas (two shown, brightness measured in number of photons with energies above 100 megaelectron volts). How these stellar explosions produce gamma rays is a mystery.

There’s a newfound source of gamma rays: explosions on the surfaces of stars. Figuring out how these novas generate such high-energy light might help astronomers understand the lifecycle of those types of stars and how they might evolve into more powerful explosions such as supernovas.

Over the last six years, the Fermi satellite, which scans the sky for gamma rays, has seen bursts of gamma radiation coming from a menagerie of sources such as pulsars and remnants of exploding stars, says Teddy Cheung, an astrophysicist at the U.S. Naval Research Laboratory in Washington, D.C. But in 2012 and 2013, Fermi detected something new — three gamma-ray bursts associated with novas. “There’s nothing in the literature that says novae can produce gamma rays,” says Cheung, who is part of the Fermi team.

Astronomers have known about novas for centuries. “When we weren’t polluted with city lights,” Cheung says, “people noticed these

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