Since the 1980s scientists have studied supermassive black holes (SMBHs) that reside at the center of most galaxies in the universe. Most recently, in April 2019, the Event Horizon Telescope (EHT) collaboration published the first image ever taken of an SBMH. These observations are a great opportunity to test the laws of physics under the most extreme conditions and offer insight into the forces that shaped the universe.
Closest SMBH to Earth
According to a recent study, a Sun-like star with strange orbital characteristics has been observed, due to the nature of the orbit the team has concluded that it must be part of a binary black hole system. In addition, it has been determined that it is the closest supermassive black hole to our Solar System, which implies the existence of a considerable population of inactive black holes in the galaxy.
The research was led by Kareem El-Badry, a Harvard Society Fellow astrophysicist at the Harvard-Smithsonian Center for Astrophysics (CFA) and the Max Planck Institute for Astronomy (MPIA). El-Badry explained that these observations are part of a broad campaign to identify inactive black holes that accompany normal stars in the Milky Way.
The mission has been measuring the positions, distances, and proper motions of nearly a billion astronomical objects such as stars, comets, asteroids, and galaxies for nearly a decade. However, this is the first attempt based on data from the Gaia Observatory of the European Space Agency (ESA), which yields positive results, since in previous attempts they only managed to obtain a collection of binaries posing as black holes.
By tracking the motion of objects as they orbit around the center of the Milky Way, the mission aims to build the most accurate 3D space catalog ever created, so El-Badry and his colleagues examined the 168,065 stars in Gaia Data Release 3 (GDR3) that appeared to have two-body orbits.
Star co-orbiting with a black hole
Through this analysis, they were able to find a G-type star designated Gaia BH1. Based on the observed orbital solution, the team has determined that this star must have a binary black hole as a companion.
Gaia’s data have determined how it moves in space by tracing an ellipse as it orbits the black hole. To confirm that this solution is correct, the star was observed with different telescopes, thus strengthening the constraints on the mass of the companion and demonstrating that it is indeed “dark”.
As in the exoplanet-hunting method, the spectra provided by these instruments allowed the team to observe and measure the gravitational forces that influence its orbit, and these observations confirmed that the mass of the black hole is about 10 solar masses.
Previous research models show that the Milky Way contains about 100 million black holes, of which only 20 have been observed. The discovery of Gaia BH1 sheds early light on this population, and if confirmed these findings could mean that there is a robust population of inactive black holes in the Milky Way.
These objects are not obvious due to the lack of bright disks, outbursts, or hypervelocity jets emanating from their poles, and if such objects are ubiquitous in our galaxy, the implications for stellar and galactic evolution could be profound. However, it is possible that this inactive black hole is an outlier and not indicative of a larger population.
To verify these findings, El-Badry and his team are awaiting the publication of data from Gaia 4 (GDR 4) which will include data collected during the five years of the mission, and from the fifth version (GDR 5) which will include data from the full 10 years of the mission.
The paper describing the findings will be published in the journal Monthly Notices of the Royal Astronomical Society.
Story originally published in Spanish in Ecoosfera