The eating habits of black holes

Astronomers have found a giant black hole with a mass of 100 billion solar masses, was caught red-handed destroying a massive star. This is the first instance that you are quite certain that the object has been recently a “diet of gas”, an important clue that also allows you to understand what kind of “food” with which they feed mostly black holes. The results of the Monthly Notices.
By analyzing archive data from the Sloan Digital Sky Survey (SDSS), and space telescopes Chandra and XMM-Newton, a team of astronomers has discovered a giant black hole that is probably destroying and devouring a massive star that it is located in its vicinity. With a mass 100 million times that of the Sun, it is to date the largest black hole caught red-handed. The results of this study are published in Monthly Notices of the Royal Astronomical Society.


Credit: SDSS/MPE.

Andrea Merloni from the Max-Planck Institute for Extraterrestrial Physics (MPE), author of the study, and the members of his group have explored the huge archive of data SDSS in view of a future satellite mission in band X. The SDSS survey noted a large fraction of the sky with his telescope optical taking a series of spectra of distant galaxies and black holes. For a variety of reasons, scientists have obtained the spectra of some objects several times. Now, when the group was analyzing one of the objects imaged with multiple spectrums, known by the acronym SDSS J0159 + 0033, a galaxy in the constellation Cetus at a distance of about 3.5 billion light years from Earth, the researchers were affected by an extraordinary change.
“Usually, the distant galaxies do not show significant changes in the course of their lives, that is, on time scales of the order of years or decades,” said Merloni. “But this showed a dramatic shift of its spectrum as if its black hole was turned on and off.” This happened between 1998 and 2005, but no one had noticed the strange behavior until last year, when two groups of researchers who were preparing the next (fourth) generation of the SDSS survey they ran independently in the data.
Fortunately, the two major space observatories X, XMM-Newton and NASA’s Chandra, observed the same area of sky near enough instant of time when there was the flare and then again ten years later . This enabled astronomers to have information only on the emission of high-energy that reveals how matter is processed in the immediate vicinity of the central black hole.
The black holes large dogs reside in the nuclei of larger galaxies. The scientists believe that their growth and development, which has achieved its current size, was due to the growth processes of the interstellar gas cannot escape their immense gravitational pull. This process takes place during a rather long time (10 to 100 million years) and is able to transform a black hole “small size”, has arisen as a result of the explosion of a massive star stellar, in an object monstrous supermassive which resides in the nuclei of galaxies.
We know that galaxies contain a large number of stars, but some of them, those less fortunate, can pass near the central black hole: here they are destroyed and finally “devoured” by the monster. If the black hole is quite compact, strong tidal interactions are literally apart the star in a spectacular way. What remains of it still spirals down around the black hole, and produces huge flares of radiation (flare) that can reach a brightness equivalent to that of all the stars in the host galaxy for a period of time ranging from a few months to a year. These rare events are called TDF which stands for Tidal Disruption Flares.
Merloni and his colleagues published their data immediately by saying that “they” flare was in almost perfect agreement with the model predictions. In addition, given the random nature of the discovery, they emphasized the fact that it was an even more particular to all those who had been found so far through active searches. With an estimated mass of 100 million solar masses, we have to deal with the biggest black hole observed in the act of destruction of a star.


Credit: J. Guillochon (Harvard University) e E. Ramirez-Ruiz (University of California)

However, the size of the system in question is not the only intriguing aspect of this particular flare but is also the first for which scientists can be fairly certain that the black hole is left recently in “diet of gas” (i.e. some tens of thousands years). This is an important clue that allows us to understand what kind of “food” they feed mostly black holes.
“Louis Pasteur said, ‘Fortune favors the prepared mind’, but in this case no one was really prepared,” said Merloni. “We could find this object only ten years ago but astronomers did not know where to look. And ‘quite common in astronomy that progress toward understanding the cosmos is often aided by serendipity. Now we have a better idea of how to identify other such events and the future instruments greatly expand our ability to research. ”
In less than two years, a new, powerful X-ray telescope, eROSITA, currently under construction at the MPE, will be put into orbit on Russian satellite-German SRG. The telescope will observe the entire sky with adequate sensitivity to detect hundreds of events of tidal destruction as in the above case. Large optical telescopes are to be designed and built in order to monitor the “variable sky” and all contribute greatly to solving the mystery of what are the eating habits of black holes. Astronomers will have to be prepared to capture these dramatic events of the life of a star, but also when they are ready, the sky still new surprises in store.

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