Astrophysicists estimate that there may be up to one billion black holes in our galaxy, most of which form binary systems — with another star or with another black hole. Such pairs can usually be detected by the behavior of the visible companion or by gravitational waves. But single black holes, which do not have satellites, are extremely difficult to detect. And now, for the first time, scientists have managed to do this.
An artist’s impression of a lonely black hole. Image credit: FECYT/IAC
It took 14 years from the first observation of the object in 2011 to the publication of the final results in The Astrophysical Journal. To confirm the discovery, the researchers looked at archival data from 16 telescopes and observed the object for six years using the Hubble Space Telescope. In the early stages, there was a possibility that the object could be a neutron star – as invisible in the optical range as a black hole. However, after lengthy studies, it was established that this is indeed the first ever recorded single black hole of stellar mass.
According to the final data, the black hole is moving along the Milky Way at a speed of about 51 km/s, its mass is about 7.15 solar masses, and the distance to it is about 4958 light years. And most importantly, it is absolutely alone, which, according to scientists, is an extremely rare phenomenon.
The discovery was made possible by the microlensing effect. The black hole’s strong gravity distorted the light of a distant background star, causing it to gradually brighten and then fade. The gravitational field also changed the star’s apparent position in the sky. However, observations were complicated by the presence of a bright light source nearby, which created significant noise in the data. Verification and analysis of the spectrograms took many years and required the use of archival observations from 16 ground-based observatories.
The decisive data came from the Hubble and Gaia space telescopes. The microlensing object OGLE-2011-BLG-0462 was located 5,153 light years away, and the invisible object that had been amplifying its light for 270 days was finally classified as a stellar-mass black hole (the hole itself is, of course, not visible in the images).
Observational data (source – background star and its bright neighbor). Stars from 2022 observations are marked in red, 2011 – in green. Image credit: The Astrophysical Journal 2025
«Our revised analysis, taking into account additional Hubble observations and updated photometry, leads to more accurate results that are fully consistent with our previous conclusions about the nature of the object,” the authors of the study note.
An additional search of the object’s vicinity at a distance of up to 2,000 AU revealed no companions with a mass greater than 0.2 solar masses, which finally confirmed the solitary nature of the black hole. It moves alone through the galaxy and is theoretically capable of becoming an unexpected threat to objects that may cross its path in the future.