Massive Star System Eta Carinae Is Shooting Cosmic Rays Towards Earth

Posted: Jul 5 2018, 11:29pm CDT | by , in News | Latest Science News

 
Massive Star System Eta Carinae is Shooting Cosmic Rays Towards Earth
Credit: NASA, ESA, and the Hubble SM4 ERO Team

Eta Carinae is the most luminous and massive stellar system within 10,000 light-years from Earth.

NASA's NuSTAR space telescope has spotted surprising changes in the behavior of a gigantic star system called Eta Carinae. The most luminous and massive stellar system within 10,000 light-years from Earth, Eta Carinae is accelerating cosmic ray particles at high speeds and perhaps some of these rays are reaching Earth.

"We know the blast waves of exploded stars can accelerate cosmic ray particles to speeds comparable to that of light, an incredible energy boost," said lead author Kenji Hamaguchi, an astrophysicist at NASA's Goddard Space Flight Center. "Similar processes must occur in other extreme environments. Our analysis indicates Eta Carinae is one of them."

Eta Carinae is located about 7,500 light-years away in the southern constellation of Carina and has already erupted twice in the 19th century, but scientists don't yet have a good explanation for those eruptions. Previous studies have suggested that the strange behavior of Eta Carinae has something to do with its structure.

Eta Carinae is a colossal binary system and consists of two massive stars revolving around each. The cooler, primary star is about 90 times massive than the sun while its companion is a smaller, hot star with a mass comparable to 30 solar massives. These stars have eccentric orbits that bring them unusually close to each other every 5.5 years. As a result, they eject powerful flow of gas called stellar winds, which engulf the stars and make it difficult for astronomers to directly measure their properties.

“Both of Eta Carinae's stars drive powerful outflows called stellar winds,” said researcher Michael Corcoran. “Where these winds clash changes during the orbital cycle, which produces a periodic signal in low-energy X-rays we've been tracking for more than two decades.”

NASA's Fermi Gamma-ray Space Telescope has detected a change in gamma rays before but the telescope is not sharp enough to provide conclusive evidence. To determine whether the interaction of the two stellar winds is responsible for periodic changes observed in the system, researchers used NuSTAR telescope which focuses X-rays of much greater energy better than any previous telescopes. By combining both newly taken and archival data, researchers confirmed that NuSTAR observations acquired between March 2014 and June 2016 coincide with lower-energy X-ray observations from the European Space Agency's XMM-Newton satellite over the same period.

The interface of the colliding stellar winds at Eta Carinae usually shows low-energy, or soft, X-rays. But NuSTAR has detected a source emitting “hard” X-rays above 30,000 eV, some three times higher than the shock waves in the colliding winds. The best explanation for hard X-rays is electrons accelerated in violent shock waves along the boundary of the colliding stellar winds, suggesting that these stellar winds are more dramatic than expected.

"We've known for some time that the region around Eta Carinae is the source of energetic emission in high-energy X-rays and gamma rays", said Fiona Harrison, the principal investigator of NuSTAR from Caltech in Pasadena, California. "But until NuSTAR was able to pinpoint the radiation, show it comes from the binary and study its properties in detail, the origin was mysterious."

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