We’re starting to detect wandering black holes hurtling through the Milky Way

The stars over 8 masses will not end in white dwarf but exploding supernovae SNII. Those with masses greater than 20/30 solar masses should not eject enough matter in the explosion so that thecollapse gravitation most often gives a neutron star, but rather a stellar black hole. Those observed have masses between 5 and 15 solar masses. They signal themselves in the Milky Way because of the material they tear from a companion star and which forms a accretion disk where forces of viscous friction between streams of matter, spiraling downwardstar compact, heat it up to the point of emitting X-rays.

But, according to astrophysicists theorists studying the birth of neutron stars and stellar black holesit may happen that the explosion is asymmetric and that consequently the final compact body is propelled as if it were a rocket. It is easy to calculate, as shown byhe course in astrophysics from the famous William Pressthan by the mere fact of its explosion in a binary system with a large loss of mass, the laws of mechanics also imply that a neutron star or a newly formed stellar black hole are catapulted at great speedsometimes to the point of being able to free themselves from the gravitational attraction of the Milky Way.

Astrophysicists therefore believe that there must be a large population of solitary stellar black holes that roam or swoop through our planet. Galaxy. The number of these objects can be estimated at approximately 100 million but there are several uncertainties regarding the models describing their birth, so actually it’s a bit more accurate to say that this number is probably somewhere between 10 million and one billion. Converselydetermining this number would make it possible to sort out these models and also to have information on the stellar and therefore chemical evolution of galaxies because they are enriched in new heavy elements with each explosion of type supernovae NS II.

But how to detect these isolated black holes since they do not accrete matter and therefore do not indirectly generate radiation?

A black hole that makes the stars shine

The general relativity gives the answer. It predicts that the field of gravitation which can end up bending a light ray which would be sent from a point very close to the surface of the events of a black hole, to the point that it falls in the direction of this black hole, is also able to deflect the rays stars in front of which this object can interpose for an observer to the point that the environment close to the black hole behaves like a gravitational lenswhich can temporarily increase the brightness of the star in front of which the black hole transits.

Astrophysicists have therefore undertaken to hunt events manifesting this phenomenon of gravitational microlensing with various instruments and two teams have just announced, via a publication in The Astrophysical Journal Letters and another in The Astrophysical Journalthat they had finally found a candidate for an isolated stellar black hole in the Milky Way.

The two teams initially based themselves on observation campaigns with photometric data which come on the one hand from theOptical Gravitational Lensing Experiment (OGLE) and on the other hand experience Microlensing Observations in Astrophysics (MOA). OGLE uses a telescope 1.3 meter telescope in Chile operated by the University of Warsaw, and MOA uses a 1.8 meter telescope in New Zealand operated by the University of Osaka. Since both microlensing surveys captured the same object, it gate two names: MOA-2011-BLG-191 and OGLE-2011-BLG-0462, or OB110462, for short.

The team led by Casey Lam and Jessica Lu at theUC Berkeley estimated the stellar black hole behind the event to be between 2,280 and 6,260 light years towards the center of the Milky Way, in the Carina-Sagittarius spiral arm of our Galaxy. She also estimates that the mass of the invisible compact object is between 1.6 and 4.4 times that of the Sun (the more massive the object, the stronger the lensing effect, so we can measure its mass). Astrophysicists are therefore cautious because it could be either a neutron star or a black hole.

But the members of the other team, led by Kailash Sahu from Space Telescope Science Institute in Baltimore (Maryland) based on the same data but also on observations from the Hubble telescope, is more certain of its assertions. For its members, the compact object is about 5,153 light-years away and above all it would have a mass of about 7.1 times that of the Sun. This time the object is too heavy to be a neutron star according to the theory of these objects, and the most likely hypothesis is that it is indeed a black hole and not a another exotic star still unknown.

Sahu’s team estimates that the isolated black hole is moving through the galaxy at the dizzying speed of 160,000 kilometers per hour, which is fast enough to travel from Earth to Earth. Moon in less than three hours.

This discovery allows astronomers to statistically estimate that the closest isolated stellar-mass black hole to Earth could be as close as 80 light-years away.