White Dwarf Explosions: A New Gamma Source

Astrophysicists have recently identified a new source of high-energy gamma ray emissions using NASA's Fermi Gamma-ray Space Telescope. Stellar explosions, called novae, have been found to release a surprising amount of gamma radiation, showing just how little we know about these rays.

A nova (not to be confused with a supernova) is a short-lived thermonuclear explosion that occurs on the surfaces of white dwarf stars - bright and hot stars that are generally no bigger than Earth. Novas have been known to release more energy than 100,000 times the annual energy output of the Sun. However, compared to the incredibly high energy processes that traditionally produce gamma rays, novae are relatively low-key.

According to Teddy Cheung, an astrophysicist at the Naval Research Laboratory, this is why researchers initially doubted Fermi readings that showed that nearby novae were releasing gamma radiation.

However, "there's a saying that one is a fluke, two is a coincidence, and three is a class, and we're now at four novae and counting with Fermi," Cheung explained in a recent statement.

A study led by Cheung that details this phenomenon is published in the journal Science.

According to the study, Fermi's Large Area Telescope first spotted a gamma-emitting nova, called V407 Cygni, in 2010. However, at the time researchers thought this must be a unique kind of stellar explosion altered by the fact that it occurred in a binary system with a red giant star.

"We initially thought of V407 Cygni as a special case because the red giant's atmosphere is essentially leaking into space, producing a gaseous environment that interacts with the explosion's blast wave," said co-author Steven Shore.

However, more classical novae detected in later years showed the same surprising gamma signatures.

The researchers now think that the colliding shockwaves produced by novae may interact with one another in such a way that they can accelerate their speeds, approaching the speed of light, ultimately producing gamma rays.

However, this is still largely speculation and much more study of gamma-producing novae must be conducted.

Nature World News recently reported on how little we actually know about gamma rays, where there are two massive but utterly mysterious bubbles of gamma radiation hovering over either pole of the Milky Way galaxy with no known source.