It is very challenging to identify dark matter because it does not produce
or reflect light or interact with electromagnetic forces. However, a study
team from The Education University of Hong Kong (EdUHK) has demonstrated
that black holes are surrounded by a significant quantity of dark matter.
The Astrophysical Journal Letters publishes the study's findings.
The crew chose two neighboring binary systems (A0620-00 and XTE J1118+480)
black holes as their study subjects. In other words, a partner star orbits
each black hole. Based on the partner stars' paths, measurements show that
their orbital decay rates are about one millisecond (1ms) per year, which is
about 50 times higher than the theoretical estimate of 0.02ms per
year.
The EdUHK team used computer models to apply the "dark matter dynamical
friction model"—a widely accepted academic theory—to the two selected binary
systems in order to determine whether dark matter is present around black
holes. The group discovered that the measured data perfectly fits the
companion stars' rapid orbital decay.
Notably, this provides indirect proof that the partner stars' orbital
speeds can be slowed down by substantial dynamical friction produced by dark
matter around black holes.
The results reflect an advance in the study of dark matter because they
supported a theoretical theory put forth in the late 20th century. The idea
is that dark matter would be consumed if it were near enough to black holes,
with the leftovers being dispersed. A "density spike" eventually forms
around the black holes as a result of the process.
According to Dr. Chan Man-ho, principal investigator and associate
professor in the department of science and environmental studies, such a
high abundance of dark matter would cause the partner star to experience
dynamical friction in a manner akin to drag force.
According to him, this is the first research to use the "dynamical friction
model" in an attempt to support and establish the reality of dark matter
surrounding black holes. "The study offers a crucial new tack for ongoing
dark matter research,"
Dr. Chan also pointed out that earlier investigations into the existence of
dark matter, which primarily relied on gamma ray and gravitational wave
detection, counted on the incidence of extremely unlikely occurrences like
the merger of two black holes. He said that might mean scientists would have
to wait a while.
But these restrictions will no longer apply to the innovative strategy used
by the EdUHK squad. "There are at least 18 binary systems similar to our
research subjects in the Milky Way Galaxy alone, which can provide rich
information to help unravel the mystery of dark matter," he continued.
Journal information:
Astrophysical Journal Letters