The astronomers' new discovery has the potential to double the number of supermassive black holes in the universe. Science has long believed that supermassive black holes are usually found only in the centers of large galaxies like our Milky Way, but the results of a new study support the idea that these objects may exist in the centers of dwarf galaxies.
The study began three years ago when astronomers from the University of Utah (USA) discovered a black hole conveniently located at the center of the ultra-compact dwarf galaxy M60-UCD1. However, more recently, the same team of scientists found two more dwarf galaxies with supermassive black holes at their centers, which suggests that such a connection is not as rare as previously predicted. The weight of this assumption is added by the fact that there may be approximately 7 trillion dwarf galaxies in the visible Universe, so it is difficult to talk about some kind of ordinary luck. What's more, new research has shown that, despite their size, dwarf galaxies can contain black holes even larger than those found at the center of our Milky Way.
“It just can't fail to impress. These ultra-compact galaxies are only 0.1 percent of the size of our Milky Way, and yet they somehow host black holes larger than the hole in the center of our galaxy,”says lead researcher Chris Ahn.
For clarity, we recommend watching the video below, which talks about how big black holes can be and how much mass they can have.
When astronomers began discovering ultra-compact dwarf galaxies in the 90s, they were immediately interested in one very strange detail - the mass of these galaxies did not correspond in any way to the mass of all the stars in them. As part of further research, it was assumed that this additional mass could be created by supermassive black holes.
“We still don't fully understand how galaxies form and develop. The black holes in their centers can tell us about how galaxies collide and merge with each other,”says An.
Using adaptive optics to more effectively observe galaxies, the researchers measured two ultra-compact galaxies: VUCD3 and M59cO. It was found that the mass of the black hole of the galaxy VUCD3 is 13 percent of the total mass of the entire galaxy. The black hole of the galaxy M59cO, in turn, accounts for 18 percent of the total mass of its galaxy. Scientists were quite surprised by this, since these indicators turned out to be much higher than those characteristic of the black hole of the Milky Way, whose mass is slightly less than 0.1 percent of the total mass of the galaxy. In addition, the results of the observations questioned the assumption that the observed objects are not actually dwarf galaxies, but are massive star clusters of hundreds of thousands of stars that appeared at the same time. Now scientists believe that these dwarf galaxies were once larger, but at one time they collided with even more massive galaxies, which tore them apart by the force of their gravity.
“We know that galaxies will collide and merge sooner or later. This is one of the essential features of the development of all galaxies in the Universe. For example, our Milky Way now, as I say this, is also devouring nearby dwarf galaxies, and after some time will collide with the more massive Andromeda galaxy,”comments one of the researchers, Anil Seth.
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“Our overall picture of how galaxies form is based on the fact that small galaxies are absorbed by larger ones over time. But the details in this picture were incomplete. Observing ultracompact galaxies, in turn, allows us to more clearly imagine the direct evolution of galaxies and find out what could have happened to these objects in the past."
The takeaway from this is that, despite their compact size, dwarf galaxies can hide the answers to the biggest questions about the universe.
NIKOLAY KHIZHNYAK