Black holes are demolishing thousands of stars in a quest to pack on weight, according to an analysis of images of 108 galaxies taken by NASA’s Chandra X-ray Observatory.
The four galaxies shown in this graphic are among 29 galaxies in the sample that showed evidence for growing black holes near their centers. X-rays from Chandra (blue) have been overlaid on optical images from the NASA/ESA Hubble Space Telescope of the galaxies NGC 1385, NGC 1566, NGC 3344, and NGC 6503. The boxes that appear in the roll-over outline the location of the burgeoning black holes. Image credit: NASA / CXC / Washington State University / Baldassare et al. / ESA / STScI.
Astronomers know that black holes ranging from about 10 times to 100 times the Sun’s mass are the remnants of dying stars, and that supermassive black holes, more than 100,000 times the mass of the Sun, inhabit the centers of most galaxies.
But scattered across the Universe are a few apparent black holes of a more mysterious type.
Ranging from 100 to 100,000 solar masses, these intermediate-mass black holes are so hard to measure that even their existence is sometimes disputed.
The new study could explain how such black holes are made through the runaway growth of stellar-mass black holes.
“One key to making intermediate-mass black holes may be their environment,” said Dr. Vivienne Baldassare from the Department of Physics and Astronomy at Washington State University and colleagues.
“We looked at very dense clusters of stars in the centers of galaxies.”
“With stars in such close proximity, many stars will pass within the gravitational pull of black holes in the centers of the clusters.”
The team’s work implies that if the density of stars in a cluster — the number packed into a given volume — is above a threshold value, a stellar-mass black hole at the center of the cluster will undergo rapid growth as it pulls in, shreds and ingests the abundant neighboring stars in close proximity.
Of the clusters in the study, the ones with density above this threshold had about twice as many growing black holes as the ones below the density threshold.
The density threshold depends also on how quickly the stars in the clusters are moving.
“This process can occur at any time in the Universe’s history, implying that intermediate-mass black holes can form billions of years after the Big Bang, right up to the present day,” the astronomers said.
The team’s paper was published in the Astrophysical Journal.
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Vivienne F. Baldassare et al. 2022. Massive Black Hole Formation in Dense Stellar Environments: Enhanced X-Ray Detection Rates in High-velocity Dispersion Nuclear Star Clusters. ApJ 929, 84; doi: 10.3847/1538-4357/ac5f51
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