This is an artist’s impression of the clash of powerful stellar winds. Credit: NASA/C. Reed
The new source confirmed that binary systems with strong colliding stellar winds comprise a separate new population of high-energy gamma-ray sources. Massive binary star systems with highly luminous and hot Wolf-Rayet stars and massive (tens solar masses) OB companion generate strong stellar winds. Its percussion may lead to producing a fierce photon flux with an energetic potential of >100 MEV, when a distance separating stars is relatively short. That phenomenon was considered a possible source of gamma-radiation for a long while.
Though such radiation was detected only once, with the famous Eta Carinae when one of its stars underwebt an explosion and for some time was the most luminous star in the sky, one example was not enough. “Recent calculations proved such star types as Eta Carinae to be incredibly rare – probably, 1 per a galaxy like we inhabit, or less,’ said Maxim Pshirkov. In 2013 an American-Austrian research team composed a list of 7 stellar systems containing Wolf-Rayet stars, where a radiation could most probably appear. This research was based on 2 years of observations and lacked data, so it was only possible to set an upper limit on the HE radiation. I decided toutilize larger set of data 7 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”
This system contains 2 stars with masses of 30 and 10 solar masses. Their orbital parameters are separated by about the same distance as Earth and Sun. The luminosity of this binary system is ~200 000 times higher than of the Sun and strong stellar winds have very high mass loss rate: hundred-thousandth and 2 10-millionth of the solar mass every year . Though these figures seem to be small, actually this amount is huge, particularly comparing to the solar wind which only amounts to 10-14 solar mass per annum As the stellar winds in the Gamma Velorum system collide >1000km/s, particles are accelerated in the shock which leads to high energy photon radiation detected by Fermi LAT.
“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,” says the scientist. “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.” http://www.eurekalert.org/pub_releases/2016-02/lmsu-afm021716.php
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