Photo credit: www.sciencenews.org
For the first time, astronomers have validated the existence of a solitary black hole—one that is not accompanied by any orbiting star. This significant discovery was led by Kailash Sahu, an astronomer at the Space Telescope Science Institute in Baltimore, who emphasized that this is “the only one so far.”
The journey to uncover this lone black hole began in 2022 when Sahu and his team identified a dark entity traversing the constellation Sagittarius. Initially, a separate research team questioned this claim, proposing that the object might be a neutron star instead. However, new observational data from the Hubble Space Telescope have now confirmed that the object’s mass is substantial enough to classify it as a black hole, as reported by Sahu’s team in the April 20 issue of the Astrophysical Journal.
The process of verifying the existence of this black hole has been lengthy and intricate. While the original discovery captured headlines three years ago, previous black holes detected have all had nearby stars that indicated their existence, with stars orbiting around them and revealing their gravitational influence. The newly confirmed black hole, however, does not possess such a companion star, making it more elusive. It became detectable when it passed in front of a less luminous background star, causing a process known as gravitational microlensing to occur. This effect magnified the background star’s light and altered its apparent position due to the gravitational pull of the black hole.
This cosmic event transpired in July 2011, and observations have shown that the star’s position continues to be affected. As Sahu explains, “It takes a long time to do the observations. Everything is improved if you have a longer baseline and more observations.”
The breakthrough was made possible by employing meticulous Hubble measurements of star positions collected from 2011 to 2017, along with supplementary data from Hubble taken in 2021 and 2022 and the Gaia spacecraft. As a result, the current estimation suggests that this black hole has a mass approximately seven times that of the sun, with a margin of uncertainty of about 0.8 solar masses. Notably, the previous uncertainty has been halved, enhancing the confidence in this measurement. Furthermore, the second research team that initially proposed an alternative theory has since revised its assessment in 2023, validating that the object is indeed a black hole with a mass around six times that of the sun, albeit with a larger uncertainty, aligning with Sahu’s findings.
This black hole is located roughly 5,000 light-years from Earth, which places it much closer than the supermassive black hole at the center of the Milky Way, located about 27,000 light-years away in the same Sagittarius constellation. The densely packed star region surrounding the galactic center is a prime area for identifying solitary black holes as they transit across stars.
Looking ahead, Sahu expressed optimism about identifying more isolated black holes, with plans to utilize the Nancy Grace Roman Space Telescope, which is scheduled for launch in 2027. This mission could significantly enhance our understanding of black holes and their distribution in the universe.
Source
www.sciencenews.org