It’s a mess out there in the universe.
In the most recent example, NASA Chandra X-ray Observatory found intermediate mass black holes that are growing destroying and consuming thousands of stars in more than two dozen galaxies. The findings indicate that massive black holes can form at any time in the history of the universe.
In a survey of 108 galaxies, Chandra identified 29 that had strong X-ray signatures emanating from nuclear star clusters, which are densely populated clusters at the centers of many smaller and medium-sized galaxies. Black holes generate X-rays when they feed on material such as torn gas of a star. The gas forms a spiraling accretion disk around the black hole as it waits to be consumed, and friction in the disk causes the gas to heat up to millions of degrees (Fahrenheit or Celsius), radiating X-rays.
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The research, led by astronomer Vivienne Baldassare of Washington State University, concludes that nuclear star clusters may be the birthplaces of intermediate-mass black holes (IMBHs), either through multiple massive star collisionsor by a massive star exploding in a supernova to create a stellar-mass black hole, which then acts as a seed for an intermediate-mass black hole (IMBH) to form through runaway growth as it destroys and consumes neighboring stars.
IMBHs have masses between 100 and 100,000 times the mass of our Sun, and on the cosmic scale they fall between stellar-mass black holes and supermassive black holes, which are found in almost all large galaxies and which contain millions, if not billions. , of solar masses.
However, so far, only a handful of IMBH candidates had previously been found, typically at the center of dense globular clusters of stars and dwarf galaxies. Finding more of these medium-sized black holes would help settle the debate over how they can form.
“Many of the theories for their formation depend on conditions that are only found in the early universe,” Baldassare said in a demonstration. “We wanted to test another theory that says they can form over cosmic time in these really dense star clusters.”
The results suggest that they can, if the speeds of the various stars in the cluster vary more than a certain amount. These circumstances cause the cluster to undergo gravitational collapse and stellar-mass stars and black holes sink to the center, instigating mergers that produce an IMBH through runaway growth.
Chandra found that nuclear star clusters that met this criterion for varying the speed of stars hosted twice as many growing intermediate-mass black holes than other clusters, supporting the theory.
Our Milky Way galaxy contains a supermassive black hole and a cluster of nuclear stars, but it remains unclear whether there is a link between the two. On a broader scale, the question of whether IMBHs are connected to supermassive black holes also remains unanswered.
The research is published in a paper in the April 20 issue of The Astrophysical Journal.
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