Two studies have confirmed the existence of a wandering black hole in the Milky Way, a lone “star ghost” without being accompanied by another star.
When stars of considerable mass reach the end of their life cycle, astrophysicists say, they transform into black holes, dense, dark objects characterized by a gravitational force so powerful that not even light escapes beyond them. They are therefore true dark hearts, which cannot be directly identified due to their nature. However, there are two techniques that allow scientists to identify the presence of a black hole: the first is related to the gravitational interaction between the “monster” and the materials that surround it, such as gases and dust that are consumed or “slaughtered” “. ”. into the deep space at relativistic speeds, i.e. close to the speed of light; the second technique, called gravitational microlensing, is related to the ability of the black hole gravitational field to distort light from a star located behind it, much further away. The wandering black hole in the Milky Way was discovered with this latest method.
The first to report it in February last year were scientists from an international team led by astronomers from the Space Telescope Science Institute in Baltimore, USA. The group also included many Italians who came from INAF, the observatories and universities of Bel Paese. Scientists led by Professor Kailash C. Sahu identified the object 5,000 light-years from Earth and calculated that it had a mass of 7.1 times that of the Sun. The scientists, who also used the Hubble Space Telescope for their analysis, determined that the mysterious object is speeding through our galactic neighborhood at a staggering 45 kilometers per second. Now, a new independent study by researchers at the University of California, Berkley, confirms the identification of the migratory black hole using the gravitational microlens technique, while highlighting some different features.
Astrophysicists led by Professor Jessica Lu and Dr. Casey Lam has actually estimated that the migratory black hole has a speed of less than 30 kilometers per second, and moreover, its mass will be between 1.6 and 4.4 times that of the Sun. This last number is quite cryptic, as black holes with a mass less than about 5 solar masses have never been discovered to date. So it could be the first such object, or it could be something else, like a wandering neutron star. But as the authors of the research point out in a press release, this is the first remnant of a dark star discovered wandering in our galaxy, not associated with another star. It can be defined as a kind of ghost star. Researchers gave it the unspeakable name MOA-2011-BLG-191 / OGLE-2011-BLG-0462.
Credit: Caltech / R. Blessé (IPAC)
“This is the first floating neutron star or black hole discovered with a gravitational microlens. Thanks to the microlens, we are able to probe these solitary and compact objects and weigh them. I think we have opened a new window. to these dark objects that cannot be seen otherwise, “said Professor Lu. Experts estimate that there are 10 million to 1 billion migrating black holes in the Milky Way, not to be confused with supermassive black holes at the center of galaxies like Sagittarius A *, whose image was recently taken by scientists from the Event Horizon Telescope project. Details of the research “An isolated black hole or neutron star with a mass gap detected with an astrometric microlens” have been uploaded to ArXiv’s online database pending publication in The Astrophysical Journal Letters.