14 DAY TRIAL // Astronomers find it very funny that the two most important forces dominating the way a galaxy looks like, behaves and travels through space cannot be detected. Though not “in league” with each other, both dark matter and black holes exert their influences through the pull of gravity.
Dark matter is believed to be a peculiar form of matter that cannot be readily detected. Yet, its influence is made visible by witnessing the gravitational effects it causes on regular matter. Conglomerations of the stuff are believed to make up about 22 percent of the mass of the Universe.
On the other hand, black holes are points of infinite density and gravitational pull, that exert such a huge attraction on everything around them, that not even light can escape, despite its speed.
Black holes, either in their solar or supermassive configuration, can be found throughout the Universe, at the core of any and all galaxies. The cosmic structures influence the behavior of stars, stellar nurseries and planetary systems in their surroundings, also through gravity.
In the past, some experts proposed connections between the existence of supermassive black holes and huge halos of dark matter. Most large galaxies that contain dark behemoths at their cores also feature dense dark matter rings around them.
Back in 2002, a group of researchers proposed that the two were connected through a fairly simple mechanism – the mass of black holes is influenced by the outer rotation velocity of the galactic disk.
In turn, that velocity is controlled by the dark matter halo extending way beyond the edges of the galaxy, the paper went on to say. Therefore, a tight connection existed between the two hidden forces in the Milky Way.
But the size of black holes has also been linked to the mass of the bulge the galaxy hosting them has. At this point, it remains unclear which factor is most influential in determining black hole growth.
In a new study from the Max Planck Institute for Extraterrestrial Physics (MPIE), experts John Kormendy and Ralf Bender sought to determine which of the two factors is more important.
“They indeed found that galaxies without a bulge – even if they are embedded in massive dark matter halos – can at best contain very low mass black holes,” an MPIE statement reads.
“Thus, they could show that black hole growth is mostly connected to bulge formation and not to dark matter,” the document goes on to say.
“It is hard to conceive how the low-density, widely distributed non-baryonic dark matter could influence the growth of a black hole in a very tiny volume deep inside a galaxy,” explains Bender, who also holds an appointment at the University Observatory Munich.
“It seems much more plausible that black holes grow from the gas in their vicinity, primarily when the galaxies were forming,” concludes Kormendy, who is also based at the University of Texas, in the US.