Published: Sun, July 08, 2018
Research | By Jody Lindsey

Cosmic radiation from giant star system heading towards Earth

Cosmic radiation from giant star system heading towards Earth

Eta Carinae, for example, is a binary star system that sits around 7,500 light years from Earth, and it's so incredibly extreme that when it fires cosmic rays off into space they actually manage to reach us here on Earth.

Yet this new study, conducted by scientists at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and published on July 2 in the journal Nature Astronomy, proves that Eta Carinae is one of the sources that blasts cosmic rays into space and possibly sends some of them our way.

Between 1838 and 1845, Eta Carinae underwent a period of unusual variability during which it briefly outshone Canopus, normally the second-brightest star. The system contains a pair of stars much more massive than our Sun and makes the brightest and most massive binary grouping within 10,000 light years of our planet. The stars contain 90 and 30 times the mass of our Sun and pass 140 million miles (225 million kilometers) apart at their closest approach - about the average distance separating Mars and the Sun. Where they collide, shockwaves are generated that can accelerate electrically charged particles to near light speed, spawning cosmic rays that likely reach Earth.

Due to the space telescope, NASA scientists now know that some of those cosmic rays are coming from Eta Carinae.

The Fermi Gamma-ray Space Telescope observes a similar change in higher-energy gamma radiation in the general direction of Eta Carinae, but the instrument does not have the resolution to confirm the source.

Eta Carinae's low-energy, or soft, X-rays come from gas at the interface of the colliding stellar winds, where temperatures exceed 40 million degrees Celsius.

Also, NASA's Fermi Gamma-ray Space telescope had been previously detecting gamma rays that contained X-rays with greater energy compared to other similarly detected gamma rays.

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"Both of Eta Carinae stars drive powerful outflows called stellar winds".

Over the last few decades, scientists have shown particular interest in Eta Carinae - seen in the southern constellation of Carina.

Now, however, NASA's NuSTAR space telescope, which is capable of detecting X-ray emissions better than the previous similar telescopes, detected high-energy X-ray emissions coming from the two massive stars of Eta Carinae binary star system.

The origin of these so-called hard X-rays varies with the orbits of the two massive stars, but the signatures of the outbursts match the gamma ray patterns first imaged by Fermi.

"The X-rays detected by NuSTAR and the gamma rays detected by Fermi arise from starlight given a huge energy boost by interactions with these electrons". "Our analysis indicates Eta Carinae is one of them".

The researchers of the current study explained that the most fitting explanation for this is that both the mysterious X-rays and the gamma rays are produced by electrons accelerating from violent shock waves along the boundary of colliding stellar winds.

"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 NuSTAR principal investigator Professor Fiona Harrison, of Caltech. "But until NuSTAR was able to pinpoint the radiation... the origin was mysterious".

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