National Aeronautics and Space Administration

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Observations of stellar eruptions, called novae, by NASA's Fermi Gamma-ray Space Telescope firmly establish that these relatively common outbursts nearly always produce gamma-rays, the most energetic form of light.

A nova is a sudden, short-lived brightening of an otherwise inconspicuous star caused by a thermonuclear explosion on the surface of a white dwarf, a compact star not much larger than Earth. Novae occur because a stream of gas flowing from a companion star in a binary system continually piles up into a layer on the white dwarf's surface. This layer eventually reaches a flash point and detonates in a runaway thermonuclear explosion.

Each nova releases up to 100,000 times the annual energy output of our Sun. Prior to Fermi, no one suspected these outbursts were capable of producing high-energy gamma-rays. Such emissions, with energies millions of times greater than visible light, are usually associated with far more powerful cosmic blasts.

Astronomers estimate that between 20 and 50 novae occur each year in our galaxy. Most go undetected, their visible light obscured by intervening dust and their gamma-rays dimmed by distance. All of the gamma-ray novae found so far lie between 9,000 and 15,000 light-years away, which is relatively nearby compared to our galaxy's size.

» https://svs.gsfc.nasa.gov/11608