Eta Carinae is one of the best-studied and most fascinating binary systems in our galaxy. Located 7,500 light-years away in the Carina Nebula, it has two massive stars (100 times and 30 times the mass of the Sun) with a combined luminosity 5 million times that of the Sun, both of which eject dense stellar winds out into space. It's shrouded in the Homunculus Nebula, a cloud of dust ejected during a violent outburst known as the Great Eruption, when the system became the third brightest star in the night sky, before fading back down.
Researchers report in two papers in Astronomy & Astrophysics (here and here) how the system also generates some of the most powerful light in the universe: X-rays and gamma rays. The researchers discovered that Eta Carinae is a source of gamma rays some 100 billion times more than the energy of visible light, making it a new source of high-energy cosmic gamma radiation.
Previous observations had shown that Eta Carinae can produce gamma-rays but the new observations, from the gamma-ray observatory the High Energy Stereoscopic System (H.E.S.S.), showed emissions 40 times more energetic than the previous detections.
The cause of the gamma rays is not the stars themselves, it's their winds. Both stars release dense supersonic streams of charged particles into space, with some moving up to 1 percent of the speed of light. The two stars also orbit each other every 5.5 years in very eccentric elliptical orbits. At their closest approach, they are approximately the distance from our Sun to Mars. At their furthest, they are as far as Uranus is from the Sun.
These motions cause the winds to periodically slam into each other with great energy. The material in the winds is heated to incredible temperatures, releasing X-rays and gamma rays. Some of these particles are accelerated by powerful magnetic fields and are thrown into the galaxy as cosmic rays. This evidence makes the binary system a new kind of source for very high-energy cosmic gamma radiation.
“The analysis of the gamma radiation measurements taken by H.E.S.S. and the satellites show that the radiation can best be interpreted as the product of rapidly accelerated atomic nuclei,” co-author Ruslan Konno said in a statement. “This would make the shock regions of colliding stellar winds a new type of natural particle accelerator for cosmic rays.”
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