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A new study using NASA's data from NASA's Space Telescope suggests that Eta Carinae, the brightest and most massive star system at 10,000 light-years, accelerates high energy particles – some of which can reach the Earth in the form of cosmic rays.
"We know that the shockwaves of exploded stars can accelerate cosmic ray particles at speeds comparable to those of light," said Kenji Hamaguchi, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. lead author of the study. "Similar processes must occur in other extreme environments. Our analysis indicates that Eta Carinae is one of them."
Astronomers know that cosmic rays with energies greater than 1 billion electron volts come from beyond our solar system. But because these particles – electrons, protons and atomic nuclei – all have an electrical charge, they deflect when they encounter magnetic fields. This confuses their paths and hides their origins.
Eta Carinae, located about 7500 light-years away in the southern constellation of Carina, is famous for its 19th-century explosion that briefly made it the second brightest star in the sky. This event also ejected a massive hourglass nebula, but the cause of the eruption remains poorly understood.
The system contains a pair of massive stars whose eccentric orbits draw them abnormally every 5.5 years. The stars contain 90 and 30 times the mass of our Sun and spread to 140 million miles (225 million kilometers) at their closest approach – the average distance between Mars and the Sun.
"The two stars of Eta Carinae lead to powerful sorties, called stellar winds," said team member Michael Corcoran, also of Goddard. "When these winds collide during the orbital cycle, which produces a periodic signal in low energy X-rays, we have been following for more than two decades."
NASA's Fermi Gamma Space Telescope also observes a shift in gamma-light rays packing much more energy than X-rays from a source towards Eta Carinae. But Fermi's vision is not as clear as that of X-ray telescopes, so astronomers can not confirm the connection.
To bridge the gap between low-energy X-ray monitoring and Fermi's observations, Hamaguchi and his colleagues are turning to NuSTAR. Launched in 2012, NuSTAR can focus X-rays much more energy than any previous telescope. The team reviewed NuSTAR's observations from March 2014 to June 2016, as well as lower-energy X-ray observations from the European Space Agency's XMM-Newton satellite over the same period.
Low energy, or mild, Eta Carinae X-rays come from the gas at the interface of colliding stellar winds, where temperatures exceed 70 million degrees Fahrenheit (40 million degrees Celsius) . But NuSTAR detects a source emitting x-rays above 30,000 eV, three times more than can be explained by shockwaves in collision winds. For comparison, the energy of visible light varies between 2 and 3 eV
The analysis of the team, presented in an article published Monday, July 2 in Nature Astronomy shows that these "hard" X-rays vary with the binary orbital period and show a model of energy production similar to the gamma rays observed by Fermi.
Researchers say that the best explanation for both hard x-rays and gamma rays is electrons accelerated by violent shock waves along the colliding stellar winds boundary. The X-rays detected by NuSTAR and the gamma rays Detected by Fermi come from the light of the stars which receives a huge boost of energy through interactions with these electrons
Some of the ultra-fast electrons, as well as some Other accelerated particles must escape the system. some end up wandering on Earth, where they can be detected as cosmic rays.
"We have known for some time that the area around Eta Carinae is the source of energy emission in X-rays and high-energy gamma rays," said Fiona Harrison, the principal investigator of NuSTAR and a professor of astronomy at Caltech in Pasadena, California. "But until NuSTAR is able to identify the radiation, show that it comes from the binary and study its properties in detail, the original was mysterious."
Learn more:
Fermi satellite celebrates 10 years of discoveries
More information:
Kenji Hamaguchi et al. Non-thermal x-rays from the collisional acceleration of the aeolian shock in the Eta Carinae binary mass, Nature Astronomy (2018). DOI: 10.1038 / s41550-018-0505-1
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