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Quasars are “eating” a huge amount of matter


Astronomers have found a population of black holes characterized by a thick accretion disk. Analysis of the data suggests that these objects, called quasars, are consuming a huge amount of matter at an extraordinary rate. The results of this study, published in the Astrophysical Journal, will provide new clues on the evolution of supermassive black holes that have existed since the primordial stages of the history of the Universe.

quasar_toro_model

Credit: NASA/CXC/M.Weiss

According to a new study conducted by the Chandra X-ray space telescope, astronomers have identified a particular population of black holes that would be consuming an excessive amount of material. This finding could provide new clues to understanding how the most massive black holes were able to grow very quickly during the early stages of the history of the Universe.
Astronomers believe that supermassive black holes, whose masses can range from a few million to a billion times the mass of the Sun and that reside in the nuclei of galaxies, can capture huge amounts of gas and dust that are attracted by their immense gravitational force. As matter falls toward the black holes, it becomes glowing and brilliant as to make them visible from great distances, up to billions of light years. These objects are called quasars.
The results of this study, published in the Astrophysical Journal, suggests that some quasars are more likely than others in attracting the surrounding matter more than has been previously imagined. “Even compared to the case of objects that are already excellent consumers of matter, these huge black holes seem to have more appetite than others, with a rate that is five to ten times higher than typical quasar,” says Luo Bin Penn State University in State College, Pennsylvania, and author of the study.
Luo and his team examined data from the Chandra satellite relative to 51 quasars that are located at a distance of between 5 and 11.5 billion light years from Earth. These objects have been selected since it showed an unusual, weak emission associated with certain atoms, in particular carbon, in the ultraviolet band. Not only that, but about 65 percent was very weak even in the X-band, about 40 times on average, compared with ordinary quasar. The weak atomic emission ultraviolet radiation and weak X may provide an important clue to the question of how a supermassive black hole attracts matter.

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Credit: NASA/CXC/Penn State/B.Luo et al.

Numerical simulations show that growth rates lower matter you have in orbit around the black hole along a thin accretion disk. If, however, the growth rate becomes higher, the disc can “inflate” dramatically, due to a significant radiation pressure, resulting in a structure called torus, donut-shaped, which surrounds the inner part of the disc.
“This model describes well our data,” said Jianfeng Wu of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts and co-author of the study. “If a quasar is surrounded by a thick frame in the shape of a bull made of gas and dust, it will absorb much of the radiation that is produced closer to the black hole and prevents it from reaching the gas that is found in the outer regions. This causes the atomic emission ultraviolet that the X-band will appear weaker.” Also the balance between the gravitational pull and the radiation pressure will be affected. “We expect that the court gives a larger amount of radiation in a direction perpendicular to the bull, rather than along the disk, which allows the material to fall into the black hole at rates higher,” added Niel Brandt of Penn State University and co-author the study.
Therefore, the most important implication that emerges from this work is that quasars characterized by a thick disk can accommodate black holes growing at an extraordinary rate. This study, along with other previous contributions, would suggest that such objects may have been very common in the universe of the origins, at least about one billion years after the Big Bang. This rapid evolution could explain the existence of black holes of large size also to ancient times.

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