The black hole at the center of the Milky Way may have a friend

This is according to the research of Prof. Samdar Naoz from UCLA, which examines the observations made of the center of the galaxy over the past twenty years and formulates theories that explain them

The black hole in the center of the Milky Way may have a friend, a massive black hole that was once at the core of a galaxy that was swallowed up within the Milky Way, and today it is apparently circling it closely, in preparation for a merger between them. This is according to a study recently published by Prof. Samdar Naoz, professor of physics and astronomy at UCLA.

In an interview with the Hidan site, Prof. Naoz, a theoretical astrophysicist, who did her doctorate at Tel Aviv University, and a postdoctoral fellow at Harvard, explains that she came to this conclusion after an in-depth examination and running over time of observations made by her experimental colleagues at UCLA, a group of whom have been following for over 20 years After the black hole in the center of the Milky Way - Sagittarius A*. It is currently estimated that the mass of the new black hole - about 100 thousand solar masses - is much smaller than the main black hole which is 4 million solar masses.

"At UCLA there is a very strong group that works on the center of the galaxy and its members have made many observations and it is very interesting to me as a theorist to understand what they see. In fact they have been watching for all these years the orbits of the stars around the black hole at the center of the galaxy.

I decided to check what we would see if there was another black hole among the stars closely circling the black hole at the center of the galaxy. The doctoral thesis I did at Tel Aviv University was on the evolution of galaxies through mergers. We have observational evidence that at the center of almost every galaxy is a massive black hole - between a million and a billion solar masses. It is clear that during the stages of the merger, the same galaxy will have two massive black holes before merging into one larger black hole.

The idea was to examine how the merger of two black holes can affect the orbits of the stars. I used an approximation of the three-body problem, where there are two large black holes and a much smaller star orbiting them. There is such a star for the Milky Way, its name is SO-2.
The very fact that there are two black holes orbiting each other affects the orbit of the star. We have a way to predict what the star will do quite accurately and on the other hand we have twenty years of observations of its actual orbit, and the ability to analyze big data., so we could test our prediction about its orbit. Although we cannot discover the second black hole, I can rule out some areas where it can exist and other areas where it cannot be found.
If there really is such a black hole, we can make further observations and focus on its mass and its distance from the big black hole, but we can already rule out the existence of a black hole with a mass of over a hundred thousand solar masses. The next step will be to use other stars and reach a better block.
Gravitational waves may help discover the new black hole

"In addition, if there really is another black hole during its orbit around the big black hole, it emits gravitational waves, so it is possible to observe them just like the signals received by the LIGO and VIRGO gravitational wave detectors, in fact the mergers whose gravitational waves were measured were of much smaller black holes. "
"However," explains Prof. Naoz: "The problem is that they emit gravitational waves at a low frequency and therefore cannot be detected by LIGO, but they will be able to be detected by the Lisa satellite which will examine gravitational waves at a lower frequency and which should be launched soon."
"The very fact that they emit gravitational waves shows that a merger took place in the not too distant past. Our studies also time-locked the process and showed that the two-hole situation could not have existed for more than 10 million years. There is evidence that the stars that are close to the center of the galaxy were formed about 6 million years ago, that is, young and new stars and orbit the center of the galaxy in relatively stable orbits. And so if a merger occurred, the black hole of the merging galaxy should have quickly reached the center of the Milky Way."
According to Prof. Naoz, the future studies, in addition to the gravitational wave studies of course, should help us improve our understanding of the history of the Milky Way, where that black hole came from, whether it was part of globular clusters that fell into the central black hole as some scientists claim. In any case, Prof. Naoz explains that we still have a lot to learn about the factor that influences us the most, except perhaps our own private sun.