The newly-discovered black hole resides in the binary system Gaia DR3 4373465352415301632 with a main-sequence star that is slightly smaller than the Sun. It is closer to the Sun than any other known black hole, at a distance of 1,550 light-years.
This image shows the location of the binary system Gaia DR3 4373465352415301632. Image credit: Sloan Digital Sky Survey / Chakrabart et al.
“Simple stellar population calculations suggest that stellar mass black holes should be abundant, with 100 millions present in the Milky Way,” said University of Alabama’s Professor Sukanya Chakrabarti and colleagues.
“However, black holes in this mass range are difficult to identify observationally.”
“Isolated black holes can only be detected with gravitational microlensing, while black holes in binary systems are easily detectable only when the companion star is close enough for accretion to be ongoing.”
“Although dozens of X-ray binaries with black hole candidates have been identified, wider binaries have proven challenging to find.”
In their study, the astronomers analyzed data for nearly 200,000 binary stars released by ESA’s Gaia satellite mission.
“We searched for objects that were reported to have large companion masses but whose brightness could be attributed to a single visible star. Thus, you have a good reason to think that the companion is dark,” Professor Chakrabarti said.
The team then observed the interesting sources using various telescopes, including the Automated Planet Finder in California, Chile’s Giant Magellan Telescope and the W.M. Keck Observatory in Hawaii.
“The pull of the black hole on the visible Sun-like star can be determined from these spectroscopic measurements, which give us a line-of-sight velocity due to a Doppler shift,” Professor Chakrabarti said.
“By analyzing the line-of-sight velocities of the visible star — and this visible star is akin to our own Sun — we can infer how massive the black hole companion is, as well as the period of rotation, and how eccentric the orbit is.”
“These spectroscopic measurements independently confirmed the Gaia solution that also indicated that this binary system is composed of a visible star that is orbiting a very massive object.”
The researchers found that the Gaia DR3 4373465352415301632 binary system harbors a black hole on an eccentric, long-period orbit.
The black hole has a mass of 11.9 solar masses; its companion — a main-sequence star — has a mass of 0.91 solar masses and an age of 7.1 billion years.
“Black holes in binary systems tend to be on short-period orbits,” Professor Chakrabarti said.
“In this case we’re looking at a black hole but it’s on a long-period orbit of 185 days, or about half a year.”
“It’s pretty far from the visible star and not making any advances toward it.”
The team’s paper will appear in the Astrophysical Journal.
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Sukanya Chakrabarti et al. 2022. A non-interacting Galactic black hole candidate in a binary system with a main-sequence star. ApJ, in press; arXiv: 2210.05003
