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Star tidal disruption flares could be used to probe black holes

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Posted November 27, 2013

Black holes eat basically everything that gets attracted by their strong gravitational pull or simply gets in their way by some sort of accident. Sometimes a black hole can be ‘lucky’ enough to be formed in the vicinity of a star. Often galaxies may host supermassive black holes which could be even capable of attracting surrounding stars to itself over longer periods of time. In any case, these events do not happen without leaving a trace: unusually abundant portions of devoured matter generate bright flares that may be even observed from the Earth.

This image of Abell 1795 shows the entire cluster of galaxies and its immediate environment. The bright filament in the center of the cluster a "cooling flow" that is denser and cooler than the surrounding gas. (Credit: NASA/SAO/CXC)

This image of Abell 1795 shows the entire cluster of galaxies and its immediate environment. The bright filament in the center of the cluster a “cooling flow” that is denser and cooler than the surrounding gas. (Credit: NASA/SAO/CXC)

Typically, a galaxy with a black hole in its center experiences a phase of high activity at some moment during its formation, when the black hole consumes the interstellar gas from its periphery. After that gas is depleted, the so-called quiescent phase of the galaxy life begins. But even then the black hole can catch stars orbiting too close to escape its gravitational potential. If that happens, the star will experience the so-called tidal disruption event: stellar material gradually accretes onto the black hole, subsequently generating bright X-ray/UV flares.

A team of scientists from the USA, Italy, Spain and the United Kingdom explored a case of a tidal disruption event, which was detected in the galaxy cluster Abell 1795 using the Extreme Ultraviolet Explorer (EUVE) and Chandra archival observations. The researchers were intrigued by the fact that a very bright point-like source was detected at the center of the cluster during the first observation by Chandra in 1999, but the intensity of light emitted by this source declined rapidly during the next seven Abell 1795 image registrations. This outburst and the following intensity decline had been also confirmed by EUVE observation performed in 1998 March 27. The team presented the results of this study in a paper published at arXiv.org.

The astronomers used seven individual observations of the flare to generate the X-ray light curve: its parameters (including the spectrum) match the character of some previously observed candidate tidal disruption events caused by a black hole. The analysis of spectral energy distribution also indicated that this flare had not been generated by a supermassive black hole but rather by an intermediate-mass black hole within 105-106 solar masses. The authors claim that TDE flares could be used to probe black holes in the intermediate mass range, which are very difficult to study by other means.

By Alius Noreika, Source: www.technology.org

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