Dark matter is the mysterious stuff that fills the universe, but no one has ever seen it. It is a hypothetical form of matter and has always been an intriguing topic in astronomy and astrophysics.

Although the nature of dark matter remains mysterious. Theoretical calculations have predicted that the dark matter density distribution would be altered by a massive black hole. Yet no promising evidence has been observed to verify this theoretical suggestion.

A research team from The Education University of Hong Kong (EdUHK) has proven that there is a significant amount of dark matter around black holes. The team chose two nearby binary systems (A0620-00 and XTE J1118+480) with black holes as their research subjects. Based on the orbits of the companion stars, measurements show that their orbital decay rate is about one millisecond (1 ms) per year, which is about 50 times higher than the theoretical estimate of 0.02 ms per year.

The team then applied the “dark matter dynamic friction model” to determine whether dark matter exists around black holes. The model is a theory that is widespread in academia – to the two chosen binary systems through computer simulations.

Scientists found that the fast orbital decay of the companion stars exactly matches the observed data.

This is circumstantial evidence of dark matter around black holes that can create significant dynamic friction, slowing the orbital velocity of companion stars. It also represents a breakthrough in dark matter research.

Dr. Chan Man-ho, associate professor in the Department of Science and Environmental Studies and principal investigator, explained that such a high density of dark matter would cause dynamic friction with the companion star, similar to the drag force.”

“This is the very first study to apply the ‘dynamic friction model’ to validate and prove the existence of dark matter around black holes. The study provides an important new direction for future dark matter research.”

Dr. Chan further mentioned that previous studies, which relied primarily on gamma rays and gravitational wave detection to investigate the presence of dark matter, depended on the occurrence of rare events, such as the merger of two black holes. According to him, that could mean a long wait for astronomers.”

Magazine reference:

  1. Man Ho Chan and Chak Man Lee. Indirect evidence for dark matter density peaks around stellar black holes The Astrophysical Journal Letters. DOI 10.3847/2041-8213/acaafa