Published: Sat, July 07, 2018
Science | By Joan Schultz

NuSTAR X-ray telescope shows Eta Carinae source of cosmic rays

NuSTAR X-ray telescope shows Eta Carinae source of cosmic rays

Scientists at NASA have discovered that a star system located some 7,500 light years away from Earth is driving high-energy particles to the speed of light, some of which might be raining down on our planet in the form of cosmic rays.

"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 and a professor of astronomy at the California Institute of Technology.

Astronomers know that cosmic rays with energies greater than one billion electron volts (eV) come to us from beyond the Solar System.

It is hard to track the origin of cosmic rays because their electrons, protons, and atomic nuclei swerve from their initial course when they collide with magnetic fields. But because the paths of cosmic rays are scrambled by magnetic fields, tracing their origins is quite hard. Every 5.5 years, their eccentric orbits see the duo pass within 140 million miles of each other.

In five and half years, the two stars in the system come within 230 million kilometers of each or roughly the average distance between Sun and Mars. The two-star system is a violent place, with its twin stars producing incredibly powerful stellar winds as they spin around each other. "Where these winds clash changes during the orbital cycle, which produces a periodic signal in low-energy X-rays we've been tracking for more than two decades".

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. 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 bridge the gap between low-energy X-ray monitoring and Fermi observations, Hamaguchi and his colleagues turned to NuSTAR.

Low-energy, or soft, X-rays originate in gas at the interface of colliding stellar winds where temperatures can exceed 40 million degrees Celsius (79 million degrees Fahrenheit).

Focused NuSTAR observations show that the colliding winds of the massive binary eta Carinae accelerate particles to very high energies, adding to the cosmic ray flux of the Galaxy. Before this, the origin of some unique X-rays and gamma rays detected on Earth was a mystery to experts.

Eta Carinae is a binary star system.

Some of these extremely fast particles crash into starlight, which boosts their light's energy, turning them into X-rays and even gamma rays, reveals the new study.

The NuSTAR detection shows that shock waves in the wind collision zone accelerate charged particles like electrons and protons to near the speed of light.

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. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). ASI provides the mission's ground station and a mirror archive.

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