Stars indicate unusual black hole in our galaxy.

By searching pictures from the archives of the Hubble World dream telescope for two and a half for decades, astrophysicists may have discovered evidence of a nearby black hole that could be at least 8,200 times as massive as the sun.

If further studies can confirm the results, the object is the second largest black hole found in our galaxy. It could also be the strongest candidate for a medium-heavy black hole-an object in the enigmatic "no-man’s country" between the ’super massive‘ black holes, which are supposedly in the center of most galaxies, and a lot of smaller ones that weigh about as much as a single big star.

fast moving stars

astrophysicist Maximilian Häberle at the Max Planck Institute for Astronomy in Heidelberg, Germany, and its employees examined more than 500 pictures of Ω Centauri, a dense star cluster with 10 million stars about 18,000 light years (5.43 kiloparsec) from the solar system. The pictures were mainly taken to calibrate the instruments of the Hubble telescope over the years.

The team put together the pictures to reconstruct the movement of more than 150,000 stars in the cluster. Most of the stars moved as the theoretical models predict, says Häberle. "But then there were some who moved faster." Seven stars, all near the center of Ω Centauri, moved too quickly to be kept solely by the cluster of gravity.

This indicates that the stars were accelerated by the gravitational force of a massive object, such as a black hole. From the speeds of the stars it would have to weigh at least 8,200 solar masses, but could weigh as much as 50,000 suns. "We didn't know beforehand whether we would find it or not," says Häberle. "It was a little risky and we couldn't have found anything."

"It is a difficult experiment", and the evidence for the existence of a black hole is "still very far from coherent," says Gerry Gilmore, an astrophysicist at the University of Cambridge, UK. In particular, the data does not show any signs that the trajectories circle from a massive object as expected, as would be the case with stars that revolve around a massive object. In the case of Sagittarius A *, the black hole of 4.3 million solar masses in the center of the Milky Way, Years of observation found irrefutable evidence for such curved railways-for the two of the leading researchers 2020 a Nobel Prize received. The GAIA playground telescope has also discovered some dormant, star-shaped black holes from the movement of a single accompanying star 2 .

Most black holes have been discovered in the past five decades by radiation such as X-rays or radio waves 3 has been detected, which is produced by overheated gas that flows into the hole in a spiral. The first indication of the existence of Sagittarius A* was actually a source of radio - if not very bright. But no such emissions were found in Ω Centauri.

puzzling middle weights

The mass of the candidate object in Ω Centauri would clearly bring it into the area of ​​medium -heavy black holes, which is generally between 100 and 100,000 solar masses. So far, the only solid evidence of black holes in this area has come from the recording of gravitational waves, which are generated by two merging black holes. Such event that was observed in 2019 is said to have created an object of about 150 solar masses.

The search for medium -sized black holes has a long history of claims that are later refuted. Astrophysicists suspected for a long time that some sources of "ultra -tumen" X -rays could be black holes of this size. But most of these candidates have now proven to be neutron stars who shine unusually brightly by taking over overheated matter from an accompanying star. "These are most likely connected to 'normal' young binary systems," says Giuseppina Fabbiano, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

There are big questions - including how some black holes become super massif and whether they are the result of several mergers, starting with stellar black holes and running by medium masses such as those of the candidate in Ω Centauri.

The team is now planning follow -up examinations with the James Webb Space Telescope, says Häberle. While the hubble data only show how the stars move over the field of vision, the spectra of the stars will show how they are moved along the line of sight, which enables astronomers to completely reconstruct their speeds in 3D.