From: Moscow Institute of Physics and Technology
Published February 15, 2017 10:49 AM

Intergalactic unions more devastating than we thought

Scientists from MIPT, the University of Oxford, and the Lebedev Physical Institute of the Russian Academy of Sciences estimated the number of stars disrupted by solitary supermassive black holes in galactic centers formed due to mergers of galaxies containing supermassive black holes. The astrophysicists found out whether gravitational effects arising as two black holes draw closer to one another can explain why we observe fewer stars being captured by black holes than basic theoretical models predict. In their study published in The Astrophysical Journal, the researchers looked into the interplay of various dynamic mechanisms affecting the number of stars in a galaxy that are captured per unit time (tidal disruption rate). (Spoiler Alert! An advanced theoretical model yielded results that are even more inconsistent with observations, leading the team to hypothesize that the disruption of stars in galactic nuclei may occur without our knowledge.) 

Tidal disruption events, or TDEs, are the only available source of information from inactive galactic nuclei. There is at least one supermassive black hole in the center of most galaxies. Surrounded by dense central star clusters, black holes occupy regions known as galactic nuclei. As their name suggests, black holes do not emit any light. However, when matter falls onto the central massive object, it gets heated to extreme temperatures and can be observed with a telescope. Active galaxies have gas clouds that feed the black hole thus making it visible. However, most of the galaxies—approximately 90 percent of them—remain “silent” because there are no gas clouds in them and so there is no matter for the black hole to feed on, except for stars that occasionally stray too close to it. When this happens, the star is pulled apart by tidal forces, experiencing what is known as spaghettification, and astronomers detect a tidal disruption event (TDE). So far, around 50 flares of radiation linked to TDEs have been observed. It is reckoned that the average rate of stellar disruption amounts to one star per 10,000 to 100,000 years per galaxy. Based on this data, the scientists are trying to develop a reliable model of what goes on in inactive galactic nuclei.

Read more at Moscow Institute of Physics and Technology

Image courtesy of NASA/CXC/U. Michigan/J. Miller et al.; Illustration: NASA/CXC/M. Weiss

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