Black holes may be swallowing invisible matter that slows the movement of stars

Two stars were observed to decelerate down in their paths around black holes, and researchers came to the conclusion that this was due to the "drag" produced by dark matter.

For the first time, researchers may have found indirect proof that black holes are surrounded by significant quantities of unseen dark matter. If the finding is verified, it could mark a significant advance in the study of dark matter.

Nearly all of the dark matter in the cosmos, which makes up about 85% of all matter, is undetectable to astronomers. This is due to the fact that dark matter is invisible and does not interact with light like the matter that makes up stars, planets, and everything else in our universe.

Fortunately, dark matter does interact gravitationally, allowing scientists to deduce its existence by observing its gravitational effects on "proxies" made of conventional matter. In the recent study, a group of researchers from The Education University of Hong Kong (EdUHK) used these stars as models for black holes in paired systems.

The team observed the paths of two stars, A0620-00 and XTE J1118+480, as they rotated around their partner black holes, decaying, or slightly slowing, by about 1 millisecond per year. The researchers came to the conclusion that the black holes' surrounding dark matter caused the stars to slow down as they whirled around their massive companions, creating considerable drag and friction.

The researchers applied a widely accepted cosmological theory dubbed the dark matter dynamical friction model to computer models of the black hole systems. This theory forecasts a particular loss of momentum on objects interacting gravitationally with dark matter. The results of the calculations showed that the friction model's forecasts were in line with the measured rates of orbital decay. In comparison to the theoretical prediction of 0.02 milliseconds of orbital decay per year for paired systems without dark matter, the measured rate of orbital decay is roughly 50 times higher.

Chan Man Ho, the team leader and an associate professor in the Department of Science and Environmental Studies at EdUHK, stated in a statement that this is the first study to use the "dynamical friction model" in an effort to validate and prove the existence of dark matter surrounding black holes.

The team's findings, which were published Jan. 30 in The Astrophysical Journal Letters, support the long-held cosmological hypothesis that black holes can consume dark matter if it approaches them closely enough. This causes the dark matter to be redistributed in the area encircling the black holes, resulting in a "density spike" there that can slightly affect the trajectory of objects nearby.

Chan stated that prior studies of dark matter in the vicinity of black holes have depended on gravitational waves or the release of high-energy light in the form of gamma rays. These emissions come from the uncommon cosmic occurrence of black holes colliding and merging, which can take a long time for scientists to gather enough evidence for.

This work offers researchers a fresh perspective on the distribution of dark matter around black holes, which may enable them to be more proactive in their quest. The EdUHK team plans to look for comparable black hole binary systems in the future to investigate.

According to Chan, "the study offers a crucial new direction for future dark matter research." There are at least 18 binary systems that are similar to our study subjects in the Milky Way Galaxy alone, and they can offer valuable knowledge that can help solve the mystery of dark matter.