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University of Alicante helps solve an enigma in the solar system neighbourhood

Prof. José Miguel Torrejón and two astronomers from Russia and Germany discover the origin of X-ray radiation emitted from star Gamma Cas after 50 years of mystery


Vecindad1Alicante. Monday, 19 December 2016

Three astronomers from Russia, Germany and Spain have resolved the enigma that has been pending for five decades on the origin of very intense X-ray radiation emitted from Gamma Cas, a bright star belonging to the constellation of Cassiopeia that can be seen by the naked eye in the heavens.

Gamma Cas, short for Gamma Cassiopeiae, is about 613 light years away from Earth which,"from the astronomical point of view, is practically in the solar system neighbourhood", as explained by lecturer José Miguel Torrejón, one of the three scientists involved, from the University of Alicante Institute of Physics Applied to Science and Technology.

It has been now 50 years with the launch of space telescopes that this star —also known by amateur astronomers— was found to be "a source of abundant X-rays", Torrejón explained. "The mechanism of production of this high-energy radiation has been a mystery that has ever since challenged astrophysical paradigms," he added.

A challenge faced by Torrejón and two of his colleagues, Professor Konstantin Postnov, from the Sternberg Institute of Moscow and Dr. Lida Oskinova, from the University of Potsdam Institute of Physics and Astronomy in Germany, who have jointly developed a theory based on known physics that solves this puzzle.

"In an article recently accepted for publication on the Monthly Notices of the Royal Astronomical Society Letters, we have proposed for the first time a theoretical model that perfectly reproduces the features of Gamma Cas objects and explains how that X-ray radiation is produced", the University of Alicante scientist said.

The model proposed by Torrejón, Postnov and Oskinova confirms the hypothesis that Gamma Cas is a binary star, with one high-mass regular celestial body and another small compact object made up of neutrons and enormous gravity which contains the mass of a sun in a ball of fifteen-kilometre radius.

The latter orbits around the first as if it were apparently a satellite, but in reality it is the old nucleus of another massive star that exploded as a supernova (the rest of the matter scattered across the space and disappeared).

According to Torrejón, and what in astronomy is called "a failed accretion (gravitational fall) in Gamma Cas objects is produced: the stellar wind material (mainly composed by protons and neutrons) form regular stars falls at a great speed on the one made of neutrons, attracted by its immense gravity".

However, this material is violently expelled as soon as the magnetosphere of the neutron star is touched by the centrifugal force of the neutron star, which is rotating on its axis at enormous speed.

In such a way that "both the material that falls on it and the ejected one collide and create a spherical layer around the neutron star that is heated to temperatures between 200 and 300 million degrees".  This hot gas is the one emitting X-ray light", as José Miguel Torrejón explained.

"We have calculated in detail the properties of this layer in the work that we have published", UA researcher said, who confirms that the theoretical predictions of the model developed jointly with the other two scientists have been spectacularly verified by observations of the X-rays".

Also, he added, our theory "accurately predicts Gamma Cas behaviour on X-rays and can be applied to other analogue stars, which have been discovered, so far a dozen in our galaxy."

"We can only study two of this kind of stars with current telescopes. One type is Gamma Cas, which is the brightest and closest to us, and the other is BZ Crux, from the Southern Cross constellation which can be observed from the Earth and is twice as long as the first one," according to Torrejón.

However,  many more bodies that emit in x-rays can be soon analysed with the launch of telescope Athena scheduled for 2028 which will carry two revolutionary instruments, one of them contributed by Torrejón's team.

For the time being, the synergy of these three researchers, each of them experts in a different field of astronomy, who met at an international conference and there since they have been exchanging their knowledge, has led science to "snatch"  one of the Universe's secrets.

Reference: “A propelling neutron star in the enigmatic Be-star γ~Cassiopeia


Gamma Cas photos: View of the star with an optical telescope and image taken by X-ray space telescope.NuSTAR.






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