Astronomer Detects New Source of High-Intensity Gamma-Radiation

February 19, 2016 | Joanne Kennell

This is an artist's impression of the clash of powerful stellar winds.
Photo credit: C. Reed/NASA

The phenomenon had only ever been detected once before!

Astronomers from Moscow, Russia, while analyzing data collected by the Fermi Gamma-Ray Space Telescope, discovered a new source of intense gamma-ray radiation.  Where did it come from?  Binary systems with strong colliding stellar winds.

Gamma-rays are a high-energy form of electromagnetic radiation, and are known to be emitted by pulsars, quasars, and stars as they collapse into black holes. Now, Russians researchers have evidence that high-intensity gamma rays can also be emitted by binary star systems — two stars close enough that their gravitational movement causes them to orbit around each other. The radiation is thought to be emitted if each star generates strong enough stellar winds that they collide with the winds of the other star.

This phenomenon was considered a possible source of gamma-radiation for more than 400 years.  However, this type of radiation had only ever been detected once, back in 2009, a long time after Eta Carinae underwent a massive explosion known as the Great Eruption in 1843.

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Eta Carinae is about 7,500 thousand light-years away, and the stars in this system weigh 120 and 30 to 80 solar masses — it shines brighter than millions of suns!

Unfortunately, one example of this new source of gamma radiation was not enough to confirm its existence, so astronomers continued to hunt for the elusive phenomenon.

“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, from the Sternberg Astronomical Institute of Moscow State University, in a press release.

In 2013, an American-Austrian research team developed a list of seven systems containing massive stars known as Wolf-Rayet stars, where a radiation burst of this sort would most likely appear.  Using this list as a reference, the researchers discovered that Gamma Velorum, a multiple star system in the constellation Vela and located about 800 light-years away, is a source for this type of gamma radiation.

Within Gamma Velorum, two stars with masses of 30 and 10 solar masses and separated by the same distance Earth is from the sun, have stellar winds colliding at a speed exceeding 1,000 kilometres per second.  This led to high-energy radiation finally being detected by Fermi.  It was not easy to detect, and it will continue to be hard to detect other binary systems undergoing the same process.

"Searching for similar sources in the […] galactic plane [plane in which the majority of a disk-shaped galaxy's mass lies] is much more complicated," said Pshirkov.  “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.”

In other words, he got lucky.  Either way, it is an amazing discovery!

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