Astronomers have discovered the closest known black hole to Earth. This historic discovery has been published in the Monthly Notices of the Royal Astronomical Society.
Black holes are astronomical objects whose gravity is so strong that not even light can escape its pull. As such, black holes are extremely difficult to observe and must be detected using indirect methods. For example, black holes can pull on nearby objects, affecting their orbits.
Astronomers at the Max Planck Institute for Astronomy and the Harvard-Smithsonian Center for Astrophysics used data from the European Space Agency’s Gaia astrometry mission to look for stars whose orbits may be affected by an unseen companion pulling on it.
Gaia’s third data release (Gaia DR3) in June 2020 is the first data release to contain the orbital data for binary systems detected with Gaia. The team used this data to find orbits that would imply that a star was in orbit with an unseen companion of considerable mass. Of the 168,065 data sets, they were able to narrow the sample down and eventually come up with one candidate star-stellar mass black hole binary system. The team named this candidate Gaia BH1.
The team performed some follow-up observations on Gaia BH1 to confirm their suspicions that this could be a binary system that contained one star and a stellar mass black hole. Stellar mass black holes are the end state of very massive stars and have masses of a few times the mass of our Sun. These follow-up observations confirmed that the Gaia BH1 system has an invisible object with a mass of about 10 solar masses which orbits a star very similar to the Sun once every 185.6 days. The distance between the star and its companion black hole is approximately the same distance between the Earth and the Sun. They also found that the binary system is 1,560 light-years from Earth, which makes the black hole the closest to Earth that astronomers have found thus far.
This is an exciting discovery, but one that also left the team scratching their heads. It is difficult to explain how such a system could have formed at all. More information about the system is needed to understand how it came to be.
