NASA's NuSTAR mission has proven that some of the cosmic rays reaching the Earth from outer space are coming from the superstar Eta Carinae.
Eta Carinae has been previously identified as the most luminous and massive star system within 10,000 light-years away from Earth. It was also found that it is accelerating particles to high energies. However, it is only until now that scientists were sure that these energies are reaching the Earth in the form of cosmic rays.
Cosmic rays with energies more powerful than 1 billion electron volts can naturally reach Earth. However, their electrons, protons, and atomic nuclei swerved from its initial course when they collide with magnetic fields. Once they reached Earth after colliding with magnetic fields, astronomers find it hard to track where they came from.
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. Astronomers earlier observed that these unique gamma rays were coming from the direction of Eta Carinae.
It was only until this present study published in Nature Astronomy on July 2 that scientists are certain these cosmic rays were coming from Eta Carinae.
Superstar Eta Carinae
Compared to older versions of space telescopes, NASA's NuSTAR is capable of focusing on X-rays with much greater energy. Since its launch in 2012, it has been detecting X-rays above 30,000 electron volts.
Some of these X-rays were even higher that they can only be coming from shock waves produced by colliding winds. When compared to the gamma rays previously detected by the Fermi telescope, astronomers observed that the X-rays seemed to be coming from the same source.
To be specific, both the high powered X-rays detected by NuStar and the gamma rays detected by Fermi seemed to be emanating from a binary orbital period. They were also showing a similar pattern of energy output.
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.
Both the X-rays and the gamma rays can only be coming from a star system that can yield a huge amount of energy produced with interacting electrons, a unique property that can only be attributed to the superstar Eta Carinae.
Eta Carinae contains a pair of massive stars whose orbits can push them closer to Earth every 5.5 years. Indeed, both of these stars drive powerful outflows called stellar winds, according to Michael Corcoran, a scientist from NASA's Goddard.
NASA's NuSTAR Space Telescope
The team behind the new study examined both new and archival data acquired by NuSTAR between March 2014 and June 2016. They also analyzed lower-energy X-ray observations from the European Space Agency's XMM-Newton satellite.
"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. 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," said Fiona Harrison, NuSTAR's principal investigator and a professor at Caltech.