The "solar winds" of the star pair Ata Karina is a strong source of radiation

Ata Karina was known to astronomers as a non-special star until 1837. Then the star began to grow and brighten due to a major eruption. For a short time in 1843 it was the second brightest star in the sky before it faded again.

A century later, in the 1940s, it began to grow again and became a variable star when small fluctuations in brightness were measured in a cycle of one to five and a half years. The great eruption of the 19th century and the other changes in its brightness in recent decades are still a mystery to astrophysicists.

At the beginning of the 20th century, astronomers noticed that Ata Karina is a relatively large and dull object, rather than a clean spot like a typical star. As the nebula spread and the telescopes improved, a large cloud of dust and gas called the homunculus nebula, shown here in the Hubble Space Telescope image, was emitted during the great eruption of the 19th century and expanded outward.

Now, the nebula's diameter is a light year. The expanding cloud contains enough material to create at least 10 objects of the size of our sun, and astronomers can not yet explain what caused this eruption.

A new study using data from the NASA's NuSTAR space telescope shows that Ata Karina accelerates particles into high energies, and some of them reach the Earth in the form of cosmic rays.

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"We know that cosmic radiation particle bursts can reach almost the speed of light, and get an energetic boost." "Similar processes must occur in extreme environments, and our analysis has shown that Atara Karina is one of these environments," said Kenji Hamaguchi, an astrophysicist at NASA's Goddard Space Flight Center in Maryland.

Astronomers know that cosmic rays with energies higher than 1 billion electron volts (eV) are constantly coming out of our solar system, but because these particles - electrons, protons and atomic nuclei - all carry an electric charge, they are removed from orbit whenever they encounter magnetic fields. This incites their paths and screens their origin.

The Atara Karina system, located about 7,500 light-years in the direction of the southern constellation Karina, was known for its 19th century eruption, which made it the second star in the sky for a short period of time. It is also surrounded by a nebula of material that spreads out as a result of the eruption but the cause of this eruption is barely understood.

The system contains a massive pair of stars 90 times the Sun and the other 30 times, orbiting each other in an elliptical orbit that brings them very close to each other - a distance of about 225 million kilometers (close to the average distance of the Mars orbit around our Sun).

"The two stars that make up the Ata Karina system emit materials in a process similar to our solar wind." Says Michael Cockorn, a research team member, also from Goddard. "When the direction of the two-star winds changes during the cycle, low-energy X waves are created, and we have been following them for more than two decades."

NASA's Fermi Space Telescope is looking at sources of radiation in the gamma-ray field, which has far more energy than X-rays from Ata Karina, but astronomers could not confirm the relationship between observations at both wavelengths. X-ray and Fermi observations, the Magucci and his colleagues approached NuSTAR. The NuStar Space Telescope launched in 2012 could focus on much higher-energy X-rays than any previous telescope.

Using NuStar's new data measured between March 2014 and June 2016, together with the low-energy observations from the European Space Agency's Newton Space Telescope, X-ray measurements turned out to be a source of interstellar winds at temperatures above 40 million degrees Celsius. However, NuSTAR recognized that the X-ray source emits more than 30,000 electron volts, three times more than can be explained by shock waves of colliding star winds. For comparison, the energy of visible light fluctuates between 2 and 3 electron volts.

The team's analysis, published in the journal Nature Astronomy, shows that the intensity of X-ray emissions varies with changes in frequencies of other wavelengths depending on the cycle of the two stars and shows a pattern similar to that of gamma rays measured by Fermi.

"The best explanation for strong X-ray radiation and gamma emission is that electrons are accelerated by strong shock waves along the boundary between the star winds," he said, adding that "the huge energy acceleration caused by the interactions of these electrons, some of them accelerating to huge velocities, The earth, here they are measured as cosmic rays. "

"We have known for some time that the area around Ata Karina is a source of strong gamma-ray emissions," said Fiona Harrison, principal investigator at NuSTAR and professor of astronomy at Caltech in Pasadena, California. "But until NuSTAR could not locate the radiation source and show it coming from a double star and studying its properties in detail, the source was unclear."

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