Astronomers Identify New Class of High Energy Gamma-Ray Sources

Massive binary star systems that generate colliding stellar winds comprise a separate new population of high-energy gamma-ray sources, say astronomers from The Sternberg Astronomical Institute.

Using data from NASA’s Fermi Gamma-ray Space Telescope, astronomers identified seven candidates of binary star systems that likely have ultra-luminous and hot Wolf Rayet stars. Their goal: find gamma-ray emissions exceeding one-hundred mega electronvolts (MeV). Only once has energies this high been observed in a binary star system – in the famous two-star system Eta Carinae.


A graphical impression of colliding stellar winds in a binary star system. Image credit: NASA/ C. Reed

“Recent calculations proved such star types as Eta Carinae to be incredibly rare – probably, one per a galaxy like we inhabit, or less,” said Maxim Pshirkov, who is the author of a study published in the journal Monthly Notices of the Royal Astronomical Society.

Of the seven systems, astronomers identified one that was the most interesting, known as Gamma Velorum. Analysis of gamma-rays showed that Gamma Velorum reached the target energies astronomers were looking for at a 6σ confidence level. Anything over a 5σ confidence is believed to be statistically accurate.

Gamma Velorum now stands along side Eta Carinae as the only two confirmed objects that are apart of this new high-energy gamma-ray category.

Gamma Velorum’s main binary contains two stars about 10 and 30 solar masses respectively. They orbit each other separated by about the same distance the Earth is from the Sun. A relatively close orbit, along with gravitational jousting between the stars likely fuels the strong colliding winds, which powers the high energy gamma-ray emissions.

The discovery was made with some luck explains Pshirkov: “Searching for similar sources in the very galactic plane is much more complicated, since it is a powerful gamma-ray source itself, and detecting small photon excess coming from colliding stellar winds becomes much more difficult with this background, but the Gamma Velorum system lies above the plane surface and it is comparatively close to us. The discovery would not probably happen, if it was further away or closer to the plane.”

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