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The powerful black holes at the center of massive galaxies and galaxy clusters act as hearts to the systems, pumping energy out at regular intervals to regulate the growth of the black holes themselves, as well as star formation, according to new data on the galaxy M84 from NASA's Chandra X-ray Observatory. An international team of scientists from the Max Planck Institute for Extraterrestrial Physics, Jacobs University, the universities of Michigan and Maryland, Baltimore County, and the Harvard-Smithsonian Center for Astrophysics contributed to the results, which now have been published in the Astrophysical Journal (doi: 10.1086/591662).
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Nov
22, 2008]
The gravitational pull of black holes is so strong that not even light can escape from them. Supermassive black holes with masses of more than a billion suns have been detected at the center of large galaxies. The material falling on the black holes causes sporadic or isolated bursts of energy, by which black holes are capable of influencing the fate of their host galaxies. The insight gained by this new research shows that black holes can pump energy in a gentler and rhythmic fashion, rather then violently.
The international team of scientists observed and simulated how the black hole at the center of galaxy M84, a massive elliptical galaxy in the Virgo Cluster about 55 million light years from Earth, repeatedly sends bubbles of hot plasma into space. Because smaller bubbles are found inside large bubbles – as shown in a Chandra X-ray Observatory image –, the impression of Russian dolls is given, where smaller dolls can be found inside large ones.
Supercomputer simulations of the interaction of supermassive black holes with surrounding gas can explain how such "Russian dolls" are created. The simulations, which were conducted by Marcus Brüggen, Professor of Astrophysics at Jacobs University, reveal the nested bubbles associated with the termination of the jet and their complex interaction with the surrounding gas, somewhat similar to the effervescent bubbles in a glass of champagne.
The dissipation of energy by sound and shock waves generated by these outbursts, as well as the additional motions they generate, are believed to be heating the gas surrounding M84. This slows down the cooling of the gas and suppresses the formation of new stars. Unless a black hole experiences a single but extremely powerful episode of activity, multiple outbursts are needed to suppress the formation of new stars and to maintain a balance between cooling and heating over long periods of time.
The observations also show that the top bubble is bursting and the hot relativistic gas, shown in red, is spilling out to the surrounding medium. The mixing of this hot gas with the cooler gas in the galaxy is an additional mode of heating of the surrounding gas by supermassive black holes that has not previously been seen so clearly.
Alexis Finoguenov, first author from the Max-Planck Institute for Extraterrestrial Physics and the University of Maryland, Baltimore County, compares the central black hole to a heart muscle: "Just like our hearts periodically pump our circulatory systems to keep us alive, black holes give galaxies a vital warm component, allowing a galaxy to maintain a fragile equilibrium," Finoguenov said.
“These results address a larger question of why galaxies stop growing after reaching a certain mass, despite containing large quantities of gas that can potentially cool and form new stars,“ says Marcus Brüggen aobout the results. If uninhibited, such cooling process would lead to the formation of many new stars and much bigger galaxies than are observed. “Outbursts generated by supermassive black holes like those in M84 provide at least one explanation for this lack of "mega-galaxies," the astrophysicist from Jacobs University concludes.
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