Exploding star ‘is firing cosmic rays towards our planet’

Rodiano Bonacci
Luglio 7, 2018

But now a NASA orbital telescope has helped pin the energy source on Eta Carinae, a double-star system around 7,500 light years away from Earth. "Similar processes must occur in other extreme environments".

It is already well established that cosmic rays with energies greater than 1 billion electron volts (eV) reach Earth from different parts of the cosmos. But because the paths of cosmic rays are scrambled by magnetic fields, tracing their origins is quite hard. It contains a pair of massive stars whose eccentric orbits bring them unusually close every five-and-a-half years. They pass 140 million miles (225 million km) apart at their closest approach, about the average distance separating Mars and the Sun.

The Eta Carinae system is made up of two massive stars that produce powerful interacting stellar winds.

"Where these winds clash changes during the orbital cycle, which produces a periodic signal in low-energy X-rays we have been tracking for more than two decades", Corcoran said.

NASA's NuSTAR space telescope has spotted surprising changes in the behavior of a very big star system called Eta Carinae.

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 make the conclusions about the origin of the cosmic energy NASA scientists examined observations from the satellite that were captured between March 2014 and June 2016, alongside lower-energy X-ray observations from the European Space Agency's XMM-Newton satellite over the same period.

The low energy X-rays, as previously suggested, was a result of the collision between hot stellar winds going up to 40 million degrees Celsius, but the "hard" X-rays had energies more than 30,000 electron volts, which is much more than what could be explained by the collision of winds. NuSTAR can focus X-rays of much greater energy than any previous telescope. For comparison, the energy of visible light ranges from about 2 to 3 eV.

The "hard" X-rays show a similar pattern as the radiation variations seen in gamma rays by Fermi and at least some of the energetic photos likely reach Earth as cosmic rays.

But, along with these low energy or "soft" X-rays, scientists at NASA also witnessed signs of gamma rays that carry much more energy. When the outflows of the two stars collide, it shoots accelerated particles into space.

"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". The star system famously brightened in 1843, briefly becoming the second brightest "star" in the sky.

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.

A new study into the properties of Eta Carinae has revealed that this "superstar", as NASA calls it, is even more intriguing than previously believed and actually shoots cosmic rays, some of which might even reach our planet. "But until NuSTAR was able to pinpoint the radiation... the origin was mysterious". Caltech manages JPL for NASA.

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