Medium-Sized Black Hole Likely Discovered

In this artist’s illustration, an intermediate-mass black hole in the foreground distorts light from the globular star cluster in the background. New research suggests that a 2,200 solar-mass black hole resides at the center of the globular cluster 47 Tucanae. (Credit: CfA/M. Weiss

(CN) – Scientists may have discovered the first example of an intermediate-mass black hole, possibly validating a long-standing theory that such “mid-sized” black holes exist.

Hidden in a nearby globular star cluster called 47 Tucanae, the black hole is the first that falls between the categories of small, stellar-mass black holes – weighing a few suns – and supermassive black holes, which can have masses up to several billion times heavier than the sun.

“We want to find intermediate-mass black holes because they are the missing link between stellar-mass and supermassive black holes,” said lead author Bulent Kiziltan. “They may be the primordial seeds that grew into the monsters we see in the centers of galaxies today.”

In a study published Wednesday in the journal Nature, the team explains how they compared the overall motions of stars throughout the center of the 47 Tucanae with easily detectable radio signals produced by pulsars – compact remnants of dead stars that get flung by the gravity of the central intermediate-mass black hole – in order to potentially discover an otherwise hidden black hole.

Scientists typically identify black holes using X-rays that come from the hot disks swirling around these cosmic mysteries, a technique that requires black holes to be actively feeding.

However, the center of 47 Tucanae is gas-free, theoretically starving any black hole that may be hidden there. This prompted the team to search for signs of a black hole within the 12-billion-year-old star cluster.

This artist’s conception shows another representation of the inter mediate-mass black hole that may lurk in the center of the globular cluster 47 Tucanae. (Credit: Bulent Kiziltan & T. Karacan)

The supermassive black hole at the center of the Milky Way influences nearby stars, which eventually enabled scientists to identify it even without direct observation of the X-rays emitted from its hot disk.

An intermediate-mass black hole at a globular cluster’s center serves as a cosmic spoon, and stirs the pot by causing stars to slingshot to greater distances at higher speeds. By employing computer simulations of stellar motions and distances, and comparing them with visible-light observations, the team found evidence for such gravitational stirring.

This – combined with evidence of pulsars – suggests the presence of an intermediate-mass black hole about 2,200 times the mass of the sun within 47 Tucanae.

The team says that the newly identified black hole’s ability to elude detection for so long suggests similar intermediate-mass black holes may be hidden in other globular clusters.

“They may be the primordial seeds that grew into the monsters we see in the centers of galaxies today,” Kiziltan said.


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