Detecting an unusual object lurking in our Galaxy, possibly a black hole

During an analysis project sifting through two decades' worth of photos from the Hubble Space Telescope archive, international astrophysicists unexpectedly found signs that could be Evidence of an unusual black hole with a mass at least 8,200 times that of the Sun is lurking in our Galaxy - the Milky Way.

To arrive at this discovery, astrophysicist Maximilian Häberle from the Max Planck Institute for Astronomy in Heidelberg, Germany, and his colleagues analyzed more than 500 images of ω Centauri, a dense cluster of 10 million stars. about 18,000 light-years (5.43 kiloparsecs) from the Solar System. These images were primarily taken to help calibrate Hubble instruments over the years.

The team stitched the images together to reconstruct the movements of more than 150,000 stars in the cluster. Häberle said most stars move as predicted by theoretical models. But then the team discovered that some cases were moving faster. Specifically, there are seven stars, all near the center of ω Centauri, that are moving too fast to withstand the cluster's gravity alone.

This suggests that the stars were accelerated by the gravity of a large object, such as a black hole. Through analyzing the velocities of these stars, scientists estimate that the object needs to be at least 8,200 times the mass of the Sun, and potentially even 50,000 times heavier than the Sun. .

Most black holes have been found in the past half century by detecting radiation such as X-rays or radio waves produced by superheated gas spiraling into the black hole. The first hint of Sagittarius A*'s presence was indeed a radio source - albeit not very bright. It is worth mentioning that no unusual jets have yet been found at ω Centauri.

But evidence for the presence of black holes is 'far from conclusive,' said Gerry Gilmore, an astrophysicist at the University of Cambridge, UK. In particular, the data show no evidence yet of curved orbits, which can happen when stars orbit a massive object. In the case of Sagittarius A*, the 4.3 million sun-mass black hole at the center of the Milky Way, astronomers have found irrefutable evidence of curved orbits. so.

The mass of the mysterious object in ω Centauri would place it in the range of intermediate-mass black holes, typically considered to have masses between about 100 and 100,000 solar masses. Until now, the only solid evidence of black holes in this range came from the detection of gravitational waves produced by two merging black holes. One such event, observed in 2019, produced an object with a mass of about 150 solar masses.

The search for intermediate-sized black holes is not a new concept in astronomy, but most have since been dismissed. Astrophysicists have long suspected that some 'ultra-luminous' X-ray sources may be black holes in this size range. But most of those candidates have now been shown to be neutron stars that shine unusually brightly due to superheated material from a companion star.

Häberle said the team is now planning further spectroscopic observations using the James Webb Space Telescope. While Hubble data only shows how stars move within the field of view, the spectra of the stars will reveal how they move along the line of sight, allowing astronomers to completely reconstruct their total velocity in 3D space.

If scientists can accurately prove the existence of this object with more in-depth studies in the future, it will become the second largest black hole found in our Galaxy. Alternatively, this could also be an intermediate-mass black hole - an object in the mysterious land between 'supermassive' black holes thought to lie at the center of most galaxies.

David Pac

Update 15 July 2024