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Thursday, July 11, 2024

Discovery of intermediate-mass black hole in Omega Centauri

Omega Centauri, located about 18,000 light-years from Earth, is the largest star cluster in the Milky Way.

Astronomers have identified a potential intermediate-mass black hole at the heart of Omega Centauri, a star cluster that is the remnant core of a small galaxy swallowed by the Milky Way 8 to 10 billion years ago. This discovery, based on the peculiar motion of seven stars, provides compelling evidence for the presence of a black hole larger than typical stellar-mass black holes but smaller than supermassive ones.

Evidence of a Mid-Sized Black Hole

Using two decades of observations from the Hubble Space Telescope, researchers led by Maximilian Häberle from the Max Planck Institute for Astronomy have detected unusual stellar movements within Omega Centauri. The cluster, containing approximately 10 million stars, exhibits a gravitational influence indicative of a black hole at least 8,200 times as massive as our sun.

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The identification of this black hole is significant due to its intermediate mass. Such black holes have been hypothesized but remain elusive, bridging the gap between stellar-mass black holes formed by the collapse of single stars and supermassive black holes found at the centers of galaxies.

Omega Centauri: A Galactic Cannibal

Omega Centauri, located about 18,000 light-years from Earth, is the largest star cluster in the Milky Way. Its origins as the core of a smaller galaxy cannibalized by our galaxy millions of years ago have been confirmed by the presence of this intermediate-mass black hole.

The researchers believe that the smaller galaxy, initially about 10% the size of the Milky Way, housed this black hole, which would have grown to supermassive status if not for the galactic merger. The collision stripped the smaller galaxy of its gas, halting the black hole’s growth and leaving it in its current intermediate state.

Hunting the Elusive Black Hole

Black holes are notoriously difficult to detect because their gravity is so strong that not even light can escape. The researchers detected this intermediate black hole by analyzing the velocity of seven fast-moving stars in its vicinity. The concentrated mass causing these stars’ rapid speeds is consistent with a black hole.

The team’s method involved building a vast database of star motions in Omega Centauri, measuring the speeds of about 1.4 million stars. This exhaustive analysis revealed the rapid motion of the seven stars, leading to the conclusion of an intermediate-mass black hole at the cluster’s center.

Implications for Black Hole Evolution

The discovery of this black hole provides a crucial piece of the puzzle in understanding black hole evolution. While stellar-mass black holes form from collapsing stars and supermassive black holes grow through mergers and accretion of gas, intermediate-mass black holes have been the missing link.

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The presence of this black hole in Omega Centauri suggests that intermediate-mass black holes may be more common than previously thought, especially in the early stages of the universe’s evolution. These mid-sized black holes could be the seeds from which supermassive black holes grow.