In January 2016, scientists of the LIGO Observatory entered history when they announced the first detection of gravitational waves. With the support of the National Science Foundation and scientists from Kaltekh and MIT, LIGO was specifically designed to search for and study these waves, predicted by Einstein’s general theory of relativity and caused by mergers of black holes.
According to a new study by a group of astronomers from the Center for Cosmology at the University of California, Irvine, such mergers are much more common than we thought. After the space survey, which was supposed to calculate and classify black holes, the university team determined that there could be up to 100 million black holes in our galaxy. This has significant implications for the study of gravitational waves.
The study recently appeared in the monthly notes of the Royal Astronomical Society. Under the leadership of Oliver D. Albert, a post-graduate student of the Department of Physics and Astronomy, scientists analyzed signals of gravitational waves detected by LIGO.
Their research began about a year and a half ago, soon after LIGO announced the first detection of gravitational waves. These waves were created by the fusion of two distant black holes, the mass of each of which was equivalent to 30 solar ones. As James Bullock, a professor of physics and astronomy at the University of California at Irvine, said, and co-author of the article:
“In fact, the detection of gravitational waves was a serious matter, as it confirmed an important prediction of Einstein’s general theory of relativity. But then we looked more closely at the astrophysics of the actual result of the fusion of two black holes with a mass of 30 solar. It was amazing, and we asked ourselves: how common are black holes of this size and how often do they merge? “
Traditionally, astronomers have held the view that black holes are usually of the same mass as our Sun. Thus, they sought to interpret the multiple gravitational waves detected by LIGO in the language of galactic formations that was already known. In addition, they also sought to create a basis for predicting future mergers of black holes.
And so they came to the conclusion that there should be up to 100 million black holes in the Milky Way galaxy, 10 million of which should have about 30 solar masses – that is, like those whose merger was discovered by LIGO in 2016. Meanwhile, dwarf galaxies – like the Dragon, which rotates at a distance of 250,000 light-years from the center of our galaxy – should contain about 100 black holes.
Further, they determined that today the majority of low-mass black holes (of the order of 10 solar masses) are in galaxies of 1 trillion solar masses (massive galaxies), and massive black holes (in 50 masses) in galaxies of 10 billion solar masses (dwarf galaxies) . After studying the relationship between the mass of galaxies and stellar metallicity, they interpreted the number of black holes of each galaxy as a function of its stellar mass.
A frequent phenomenon?
In addition, they also tried to determine how often black holes appear in pairs, how often they merge and how much time it takes. The analysis showed that only a small part of the black holes should participate in the merger in order to explain the observations of LIGO. He also proposed forecasts that showed that in the next decade even larger black holes should merge.
As Manoha Kaplinghat, professor of physics and astronomy, who took part in the study, says:
“We showed that only 0.1-1% of black holes should merge in order to explain what LIGO saw. Of course, black holes must be close enough to merge at a certain time, and this problem remains open … If current ideas about the evolution of stars are correct, our calculations show that fusions of even 50 solar masses should be detected in a few years “.
In other words, our galaxy can abound with black holes, and mergers can occur on an ongoing basis (by cosmological measures). Thus, we can expect that in the coming years in the future there will be new opportunities for detecting gravitational waves. This should not surprise, since the winter of 2016, LIGO has made two more discoveries.