In the universe, there is a serious gap between the number of black holes that have been discovered and the expected number. One of the reasons is that black holes are low-key and no one can find them. Maybe they are lurking nearby, but we can’t see them. But recently, a team of astronomers appears to have detected, for the first time, a “wandering black hole” wandering alone in the Milky Way, just 5,150 light-years away.
Although black holes are extremely gravitational, they may be the darkest objects in the universe. Scientists usually have to know of black holes through other means, such as the hot accretion disk orbiting the black hole, the bright light released by the black hole when it devours the stars, and being affected by the black hole. Orbiting celestial bodies, or gravitational waves caused by collisions with other massive objects.
Although there are many indirect ways to find black holes, in fact, there is a huge gap between the number of black holes we have found and the predicted value of the model. For example, there should be at least 100 million stellar black holes in the Milky Way (a star with a mass of more than 20 solar masses will die when it dies. A recent study also predicted that there are at least 40,000,000,000,000,000,000 stellar black holes in the universe. This number does not include supermassive black holes and theoretical intermediate-mass black holes.
Astronomers have long predicted that stellar black holes should be ubiquitous, but largely invisible because they don’t interact with others. But these “isolated” black holes can manifest themselves in one way – the gravitational lensing effect: when a black hole passes in front of a background light source, the strong gravity slightly distorts distant light to brighten and “bend” it. For decades, astronomers have Close attention has been paid to gravitational lensing events that cannot be explained by visible objects such as stars and galaxy clusters, which may indicate the existence of an invisible black hole there.
The more massive the object that causes gravitational lensing, the longer it takes to brighten the background light source, and if the object is a black hole, the microlensing event lasts longer and doesn’t emit any detectable light itself .
Now, for the first time, astronomers may have solid evidence of a wandering black hole.
Combining 6 years of observational data from Hubble and ground-based telescopes, scientists discovered a 270-day microlensing event, called MOA-2011-BLG-191/OGLE-2011-BLG-0462, estimated to be a mass of about the Sun 7.1 times the size of a stellar black hole and moving at about 45 kilometers per second, much faster than the stars around this region of the Milky Way.
The research team estimates that the black hole may have been born about 100 million years ago, but there is no clear path to trace the origin of the black hole. In the future, the Roman Space Telescope (formerly the WFIRST Wide-Field Infrared Survey Telescope) and the Vera C. Rubin Observatory (formerly the LSST Large Synthetic Survey Telescope) in Chile may help find more strays Stellar black hole.