Lonely stellar black hole found in the Milky Way for the first time

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A team of astronomers has unequivocally detected and measured a stellar black hole roaming the Milky Way for the first time. This follows from a research paper submitted to the Astrophysical Journal for publication. If the discovery announced in it is confirmed, it will be a milestone in astronomy, because although black holes of several solar masses are probably very common, they are difficult to detect. While there are only candidates for such objects, there is no confirmed find in the Milky Way. What has now been discovered was issued by the star before which it passed from our point of view.

Like a team of dozens at the Kailash Sahu Space Telescope Science Institute in article published on Arxiv This is explained by the fact that the black hole was discovered due to the so-called microlensing effect. An object in front of a star causes light rays to bend in such a way that it appears magnified to us. In 2011, this was observed in a star that we believe is in an extremely dense field towards the center of the Milky Way. For 270 days it was significantly brighter than before and after. Just weeks after the MOA-2011-BLG-191/OGLE-2011-BLG-0462 event, the Hubble Space Telescope pointed to it and confirmed that the star was slowly fading again.

Using the measurement data collected in this way, astronomers calculated that the lens responsible for brightening should have a mass of about 7.1 solar masses. If it were a star, it would have to be visible, too massive for a white dwarf or neutron star. They explain that even a binary system of such objects cannot reach such a mass. So even if a binary star system caused the brightness, there must be a black hole inside, but that’s unlikely. The most likely explanation is a single stellar black hole of this mass. It is about 5,200 light-years away, alone in the Milky Way, and moving much faster than the stars in its vicinity.

Observed change in brightness

(Image: “Isolated stellar-mass black hole detected by astrometric microlensing”, Kailash Sahu et al.)

Stellar black holes are formed as a result of the collapse of massive stars. Since, once formed, they are mostly dormant and do not suck up material that heats up and becomes visible, they are difficult to find. At the same time, they must be immensely numerous because of this way of origin. Just a few days ago, a research team from Italy presented calculations that there should be 40 trillion stellar black holes in the observable universe. For the Milky Way alone, models suggest 100 million such objects. Sahu’s team expects future telescopes to observe many thousands of microlensing effects like the one that led to the discovery of the first black hole of its kind. This should be used to search for many other stellar black holes.


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