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When a star dies


The long glow in X-rays coming from Abell 1795 galactic storage recorded by NASA’s Chandra space telescope would be the last act of the end of a star torn apart by an intermediate-mass black hole.

Abell 1795

Source: X-ray, NASA / CXC / Univ. of Alabama / WPMaksym et al & NASA / CXC / GSFC / UMD / D. Donato, et al, in the optical band, CFHT

Composite image in the x-ray (blue) and in the visible light of the mass of galaxies called Abell 1795. In the box indicates the area where the Chandra Space Telescope has observed the appearance and the occurrence, in 2005, the glow in X-rays associated with the destruction of a star by the gravitational force exerted by an intermediate-mass black hole, as it can be seen in the two panels in the lower left.

An X-ray source in the sky mysteriously turns on and after a few years, just as mysteriously disappears. The place is a dwarf galaxy about 800 million light years from us, which is part of the giant galaxy cluster Abell 1795. A complicated ‘ case ‘ for two teams of astronomers who have studied the phenomenon and, independently, came to the same conclusion: the long X -ray burst, which was monitored on several occasions by NASA’s Chandra orbiting telescope between 1999 and 2005, was none other than the ultimate sign of a dramatic end, that of a star approached them too close to a black hole and disintegrated by its immense gravitational pull.

An event not too rare in the universe is already known fact other candidates incidents of destruction due to stellar blacks holes. To make it still amazing though is the fact that it would be the first to be observed in a relatively small size of the galaxy, which contains about 700 million stars. In comparison, the Milky Way has over a hundred billion. This implies that the black hole responsible for the crime would not be as massive as those of the supergiant ordinary galaxies, i.e. with masses of millions or billions of times that of the Sun, but ‘ just ‘ a few hundred thousand. Then would lie between those of stellar size (of the order of 10 solar masses), and, of course, those ‘ extralarge ‘. A very interesting category for astronomers that could represent the progenitors of supermassive ones. Discover celestial objects of this type could reveal how they have evolved the first galaxies at the dawn of the universe.

“Scientists are looking for these black holes of intermediate mass for decades,” emphasizes the Italian Davide Donato, in force at Goddard Space Flight Center (GSFC) of NASA in Greenbelt, USA, who led one of the two teams involved in the study. “So far we have collected a lot of information on the small and very large ones, but the intermediate ones are difficult to characterize.”

Identify the culprit would have been almost impossible in this case if the scientists had not had a large amount of observations of the same region of the sky repeatedly over a wide range of time, just like those of Chandra related storage Abell 1795 because that object celestial orbiting observatory is usually aimed to calibrate its instruments .

“The star was destroyed by passing too close to the black hole is undetectable, but the release of energy during its destruction but it is. And the study of the issue observed, its intensity and evolution with time, has allowed us to associate it convincingly to a phenomenon of tidal destruction (tidal disruption, in English), excluding other phenomena of interaction between the black hole and matter in order to explain what has been observed, “says Stefano Covino, INAF, which together with colleagues Sergio Campana and Dino Fugazza have partnered with Donato in the study, published in the journal The Astrophysical Journal.

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