A new source of intense gamma-radiation in the sky has been discovered. With the help of the Fermi Gamma-ray Space Telescope, Maxim Pshirkov found out that the binary star systems with strong colliding stellar winds produce gamma-rays.
“Recent calculations proved such star types as Eta Carinae to be incredibly rare – probably, one per a galaxy like we inhabit, or less. My colleagues’ research resulted in no certain findings. I decided to utilise larger set of data seven years of Fermi-LAT observations. As the result – it was discovered that Gamma Velorum is the source of gamma-radiation at 6.σ. confidence level,” says Pshirkov.
This has two stars that weigh 30 and 10 solar masses, respectively. The scientist notes that the luminosity of this binary system is 200,000 times higher than the Sun and the strong stellar winds lose about a hundred-thousandth and two ten-millionth of the solar mass annually. When Gamma Velorum’s winds collision goes beyond 1,000 kilometres per second, the particles are accelerated in the shock, leading to a high energy photon radiation.
The study, published in the Monthly Notices of the Royal Astronomical Society Letters, states that the radiation has been detected before in the stellar system Eta Carinae. In 1834, one of its stars exploded and became the brightest star in the sky. The system has been observed by scientists for four centuries and contains two stars that weigh 30 and 90 solar masses respectively, which shine brighter than millions of suns.
“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,” Pshirkov concludes. “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.”