Swarm of black holes discovered

[Judi Lynn]

Posted by Kelly Whitt in SPACE | February 21, 2021
For the first time, astronomers have detected the presence of a throng of black holes crowding near the center of an ancient globular cluster.

In this episode of Space Sparks, ESA/Hubble summarizes their findings.

Sometimes in science when you set out to find something you had predicted, you instead find something quite different. This was the case recently when astronomers using the Hubble Space Telescope examined the core of a globular cluster, a “ball” of densely packed old stars named NGC 6397, looking for one central intermediate-mass black hole. Instead they unexpectedly found a whole swarm of small black holes, as reported by NASA and ESA on February 11, 2021.

There are two well-established types of black holes: the stellar-mass black hole that is formed when a large star runs out of fuel and collapses and weighs just a few times the mass of our sun, and the supermassive black hole that is believed to exist in the center of every large galaxy and contains the mass of many millions of stars. Apart from these two types, astronomers believe that a middle-of-the-road type of black hole should also exist – the intermediate-mass black hole, with a mass of 100 to 100,000 times the mass of our sun – and there are several candidates for these but only a few confirmed cases.

These researchers’ analysis of data from the Hubble Space Telescope and Gaia Space Observatory on this globular cluster did not provide the evidence of a medium-sized black hole at its core that the astronomers were looking for. Instead, they made the very first detection of a collection of black holes at the center of a globular cluster.



The globular cluster NGC 6397, containing hundreds of thousands of stars, was imaged by the Hubble Space Telescope. The cluster’s blue stars are hotter and near the end of their lives, while orange ones are expanded red giant stars. The white stars include stars that are similar to our sun. Image via NASA/ ESA/ T. Brown and S. Casertano (STScI).

Astronomers targeted this particular globular cluster, NGC 6397, because at 7,800 light-years away, it’s one of the closest globular clusters to Earth. More importantly, scientists think that a globular cluster is an ideal place to find medium-sized black holes because of the dense collection of stars at their cores.

More:
https://earthsky.org/space/group-black-holes-found-globular-cluster-ngc-6397

[PJMcK]

1. It's Black Hole Day!

Great articles. Thanks, Judi Lynn.