Observations of several stellar eruptions, called novae, by NASA’s Fermi Gamma-ray Space Telescope firmly establish these relatively common outbursts almost always produce gamma rays, the most energetic form of light.
“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,” said Teddy Cheung, an astrophysicist at the U.S. Naval Research Laboratory in Washington, and lead author of a paper reporting the findings in the August 1 edition of the journal Science.
A nova is a sudden, short-lived brightening of an otherwise inconspicuous star resulting from a thermonuclear explosion on the surface of a white dwarf, a compact star not much larger than Earth. Each nova explosion releases up to 100,000 times the Sun’s annual energy output. Prior to the Fermi observations, no one suspected these outbursts were capable of producing gamma rays, emission with energy levels millions of times greater than visible light and usually associated with far more powerful cosmic blasts.
Fermi’s Large Area Telescope (LAT) scored its first nova detection, dubbed V407 Cygni, in March 2010. The outburst came from a rare type of star system in which a white dwarf interacts with a red giant, a star more than a hundred times the Sun’s width. Other members of the same unusual class of stellar system have been observed “going nova” every few decades.