The newly discovered intermediate mass hole, named NGC 6099 HLX-1, lies in a compact star cluster at the periphery of the Elliptical Galaxy NGC 6099, around 40,000 light years from the center of the galaxy.
Radiography and infrared images of NGC 6099 HLX-1. Image credit: NASA / CXC / INST. Astronomy, Taiwan / YC Chang / ESA / STSCI / HST / J. Depasquale.
NGC 6099 is located at around 450 million light years in the Constellation of Hercules.
Astronomers first saw an unusual source of X -rays in an image of this galaxy taken by the NASA X -ray observatory in 2009.
They then followed its evolution with the ESA XMM-Newton Spatial Observatory.
“X-ray sources with such extreme brightness are rare outside the nuclei of the galaxy and can serve as a key probe to identify the elusive black holes of intermediate mass,” said Dr. Yi-Chhi Chang, astronomer of the National University of Hua Tsing.
“These objects represent a lacking crucial link in the evolution of black holes between the stellar mass and the supermassive black holes.”
The issue of X-ray from NGC 6099 HLX-1 has a temperature of 3 million degrees compatible with a tide disturbance event.
Using the NASA / ESA Hubble space telescope, astronomers found evidence of a small group of stars around the black hole.
This cluster would give the black hole to feast on, because the stars are so closely filled together that they are only a few months of light (about 500 billion miles).
The black hole suspected of intermediate mass reached maximum brightness in 2012, then continued to decrease to 2023.
Optical observations and X -rays during the period do not overlap, which complicates interpretation.
The black hole may have torn a captured star, creating a plasma disc that displays variability, or it may have formed a disc that sparkles while the gas falls to the black hole.
“If the intermediate mass hole eats a star, how long does it take to swallow its gas?” said Dr. Roberto Soria, astronomer from the Italian National Institute of Astrophysics.
“In 2009, HLX-1 was quite brilliant. Then in 2012, it was about 100 times brighter. And then he returned. “
. “So now we have to wait and see if he gets out several times, or there was a start, there was a peak, and now it will just go until he disappears.”
The authors point out that making an investigation into intermediate mass holes can reveal how larger supermassive black holes are formed in the first place.
There are two alternative theories. The first is that the black intermediate mass holes are the seeds to build even larger black holes while coming together, because the large galaxies develop by taking smaller galaxies. The black hole in the middle of a galaxy also pushes during these mergers.
Hubble’s observations have revealed a proportional relationship: the greater the galaxy, the bigger the black hole. The emerging image with this new discovery is that the galaxies could have black satellite intermediate mass holes which orbit in the halo of a galaxy but do not always fall in the center.
Another theory is that gas clouds in the middle of black matter halos in the early universe do not first make the stars, but collapse directly in a supermassive black hole.
The discovery by webb of very distant black holes being disproportionately more massive compared to their host galaxy tends to support this idea.
However, there could be an observation bias towards the detection of extremely massive black holes in the remote universe, because those of smaller size are too low to be seen.
In reality, there could be more variety in the way our dynamic universe builds black holes.
Supermassive black holes collapse inside black matter halos could simply develop in a different way from those who live in dwarf galaxies where the accretion of black hole could be the privileged growth mechanism.
“So if we are lucky, we will find more floating black holes becoming suddenly brilliant because of a tide disturbance event,” said Dr. Soria.
“If we can do a statistical study, it will tell us how many of these black intermediate mass holes are, how often they disturb a star, how larger galaxies have grown up by assembling smaller galaxies.”
The results were published in the Astrophysical Journal.
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Yi-Chi Chang and al. 2025. Multiple wavelength study of a hyperluminous X -ray source near NGC 6099: a strong IMBH candidate. APJ 983, 109; Two: 10.3847 / 1538-4357 / Adbbee
