A star per year: this is the rate with which supermassive black holes swallow the matter in the galaxies of which they are part, or at least some of them. This is stated in a study published in "The Astrophysical Journal" by astrophysicists of the University of Colorado in Boulder. The article emphasizes in particular that this destructive outcome for the individual stars is part of an overall picture of interactions and forces that defy certain laws of physics.
Credits
At the center of many galaxies there is a supermassive black hole that creates a cluster of stars around itself as a result of a very intense gravitational attraction. Now, physics would like this cluster to have a spherical symmetry geometry. Instead, observations show that different galaxies, including our neighbor Andromeda, have an asymmetric cluster, which takes the form of an eccentric disk, because the whole structure revolves around a point that is not the geometric center of the disk.
Studies in this field have hypothesized that such eccentric disks are the result of a merger between two galaxies. This is the big picture, but what happens inside a record?
Each star follows an elliptical orbit. Often the orbits of the stars almost overlap and interact with each other. Finally, gravitational disturbances they can carry an orbit too close to the black hole.
" The force that accumulates in these stellar orbits changes the shape of the orbits themselves," explained Ann-Marie Madigan, co-author of the study. "In the end, the star that is involved in this process reaches the point of minimal approach to the black hole and is cut to pieces".
The result supports the hypothesis that the stellar mortality of some galaxies with supermassive black holes in the center is higher than that of other types of galaxies.
"We predicted that in the period following the merger of galaxies, a super-massive black hole swallows a star a year," said Heather Wernke, co-author of the paper. "It's a 10,000-fold process more frequent than expected by other studies ".
Finally, the study suggests that an eccentric disk in the center of a galaxy may be more common than expected. This is a hypothesis that will be verified with the next studies, which should also allow us to better understand the mergers between galaxies and the evolution of the universe.
"Andromeda probably has already passed the peak of this process, because it is the result of a galactic fusion that took place a long time ago," concluded Madigan. "With a higher resolution, we could discover younger eccentric discs in more distant galactic nuclei."
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