At the center of the Milky Way is there a supermassive black hole, Sagittarius A *, or a concentration of dark matter?.
At the heart of the Milky Way is a supermassive black hole that astronomers have called Sagittarius A * (Sgr A *). Its existence has been taken for granted for some years and the studies it was subjected to even earned the Nobel Prize in Physics 2020 to the American astronomer Andrea Ghez and the German astrophysicist Reinhard Genzel.
Yet now a new hypothesis, which brings up dark matter , questions this certainty. In fact, no one has ever seen the black hole, because a black hole is impossible to see (to begin with): astronomers have deduced its presence based on the gravitational effects it exerts on the objects that populate our galaxy, in particular on the stars that orbit near it.
ScienceHere is the first photo of a black hole
THE NEW HYPOTHESIS. But now a group of researchers from Italy, Colombia and Argentina argues that the same effects could be observed even if there were a gigantic mass of dark matter . Indeed, according to the researchers – who published the study in Monthly Notices / Letters of the Royal Astronomical Society – this hypothesis would explain certain phenomena even better.
The team’s suspicion was aroused by the strange behavior of an object called G2– whose exact nature is still unknown to astrophysicists, although for some it seems to be what remains of a binary star system – when it passed close to Sagittarius A *. The G2 object has miraculously emerged unscathed from the encounter with the alleged supermassive black hole, which should have a mass comparable to 4.1 million times the mass of the sun .
Everything we know about the Universe is summed up in the rooster segment of this pie chart: just under 5% of everything . This meager amount corresponds to what we call ordinary matter : nebulae, galaxies, stars, planets, ourselves … Of all the rest we can only say that there should be about 27% (in energy) of dark matter (which corresponds to the 85% of all matter we suppose to exist), and about 68% of an even more mysterious dark energy , of which we know nothing. For further information: fog on dark matter .
How it is possible that such a close encounter with a black hole has left this object intact is very difficult to explain, while it would not be if, instead of the black hole, one assumed the presence of a concentration of dark matter equal to about 500,000 masses solar. The researchers also hypothesize that dark matter could be made up of exotic particles called darkinos : they would be ultra-light neutral particles that, kept in equilibrium by their own gravitational attraction, would form a “ball of matter” with blurred outlines whose gravitational attraction would not have been enough. strong to destroy G2.
What gives consistency to this hypothesis is that it allows us to explain the behavior of the 17 stars that rotate very close to the heart of the Milky Way. Hypothesis of the black hole Sgr A * to be deleted then? Astronomers are on high alert, but for this hypothesis to become a theory, there must be other similar observations in other galaxies. It would also be necessary to explain other phenomena that are currently consistent with the hypothesis of supermassive black holes in the heart of galaxies, such as the jets of energy observed starting from some of them.
