Astronomers have confirmed the existence of a solitary black hole for the first time. The black hole, located in the constellation Sagittarius, was initially disputed as potentially being a neutron star but new observations from the Hubble Space Telescope have confirmed its massive size, indicating that it is indeed a black hole. This discovery is significant as previous known black holes were all accompanied by companion stars, making this solitary black hole unique.
The reason these solitary black holes are hard to find is that they do not have companion stars to betray their presence. The black hole in Sagittarius was discovered when it passed in front of a background star, magnifying and shifting its position due to the black hole’s gravity. This passing occurred in July 2011, and the star’s position is still changing, requiring long-term observations to confirm the presence of the black hole definitively.
The discovery of the Sagittarius black hole was based on precise Hubble measurements of star positions from 2011 to 2017, with additional data from 2021 and 2022, as well as data from the Gaia spacecraft. The black hole’s mass was estimated to be about seven times that of the sun, with a smaller margin of error compared to previous estimates. Another research team independently confirmed the object as a black hole, with similar mass estimates, further validating the discovery.
Situated 5,000 light-years from Earth, this black hole is much closer than the supermassive black hole at the center of the Milky Way. The region around the galactic center, including Sagittarius, is rich in stars and provides an ideal environment for uncovering solitary black holes passing in front of stars. The discovery offers insights into the prevalence and nature of black holes in our galaxy.
Moving forward, astronomers plan to leverage the upcoming Nancy Grace Roman Space Telescope, expected to launch in 2027, to search for additional solitary black holes. The advanced capabilities of this telescope will enhance the search for these elusive objects and contribute to a better understanding of their distribution and properties within the Milky Way. As technology and observations continue to improve, more solitary black holes may be discovered, shedding light on their mysterious and intriguing nature.
