Washington, Eta Carinae, the most luminous and massive stellar system within 10,000 light years, is accelerating particles to speeds comparable to that of light — some of which may reach Earth as cosmic rays, suggests a new study.
“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 the lead author of the study Kenji Hamaguchi, an astrophysicist at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland.
“Similar processes must occur in other extreme environments. Our analysis indicates Eta Carinae is one of them,” Hamaguchi said.
Astronomers know that cosmic rays with energies greater than one billion electron volts (eV) come to us from beyond our solar system.
But because these particles — electrons, protons and atomic nuclei — all carry an electrical charge, they veer off course whenever they encounter magnetic fields. This scrambles their paths and masks their origins.
For this study, published in the journal Nature Astronomy, the researchers used data from NASA’s NuSTAR space telescope.
Launched in 2012, NuSTAR can focus X-rays of much greater energy than any previous telescope.
Using both newly taken and archival data, the team examined NuSTAR observations acquired between March 2014 and June 2016, along with lower-energy X-ray observations from the European Space Agency’s XMM-Newton satellite over the same period.
“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.
“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 Harrison, who also serves as a professor of astronomy at California Institute of Technology (Caltech) in Pasadena.
Eta Carinae, located about 7,500 light-years away in the southern constellation of Carina, is famous for a 19th century outburst that briefly made it the second-brightest star in the sky.
This event also ejected a massive hourglass-shaped nebula, but the cause of the eruption remains poorly understood.
The system contains a pair of massive stars whose eccentric orbits bring them unusually close every 5.5 years.
The stars contain 90 and 30 times the mass of our Sun and pass 225 million km apart at their closest approach — about the average distance separating Mars and the Sun.