There were more massive black holes in the early universe than previously thought, a new study suggests.
A new method to predict the mass of the largest massive black hole believed to be hiding in the center of most galaxies has shown that these cosmic titans can grow faster than previously believed.
The results, from new computer modeling techniques, suggest that, billions of years ago, black hole could be bigger than scientists thought. This is a potential breakthrough, as it could help researchers understand how supermassive black holes reach such massive sizes.
“The black hole at the center of our galaxy is millions of times the mass of the daybut we also see others that we think are billions of times the mass of the sun,” study author Joseph Simon, a postdoctoral researcher at the University of Colorado, Boulder, said in a statement. “We have really good measurements for the mass of supermassive black holes for our own galaxy and for galaxies nearby. We don’t have the same kind of measurements for galaxies that are more distant. We just have to guess. “
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The two supermassive black holes described by humanity so far serve as startling examples of just how massive the scope of these cosmic monsters can be. Sagittarius A* (Sgr A*), in the heart of Milky Way, has a mass equal to about 4.5 million suns. The black hole hidden within the galaxy M87located about 6 million light-years away, has a mass equal to about 5 billion suns, however.
There are several theories about how supermassive black holes grow to incredible sizes, most of which involve mergers of smaller black holes.
But there’s a problem with this idea: Has there been enough time in the 13.8-billion-year history of the universe for these processes to have grown massive black holes, especially those that existed billions of years ago?
“There was an expectation that you could only see this massive system in the nearby universe,” Simon said. “Black holes take time to grow.”
Black holes were massive in the early universe
As the colliding black holes spin around each other, they send out gravitational waves – ripples in space-time that Einstein’s theory of general relativity It is said to be created by massively accelerating objects — streaming out into space. The final collision of the black holes sends out a massive burst of gravitational waves that signal the merger. Some of these waves reach Earth and carry information about the events that created them.
Simon is part of an effort called North American Nanohertz Observatory for Gravitational Waves (NANOGrav), which looks for a continuous stream of gravitational waves called the “gravitational wave background.” But, to fully understand it, scientists need to know the mass of the supermassive black hole through cosmic history.
To develop a new method of determining black hole masses, even for distant examples, Simon gathered information about hundreds of thousands of galaxies, some of which are so far away that the they were like billions of years ago. With this data, the researcher calculated black hole masses for some of the largest galaxies in the universe. He then used computer modeling to simulate the gravitational waves which will create these things.
This gave Simon a mass spread for black holes in the universe dating back around four billion years. The data revealed something unexpected: There was a greater selection of massive galaxies and massive supermassive black holes in the the galaxy billions of years earlier than currently predicted.
New research suggests that this supermassive black hole may not need as much time to grow as previously theorized. Similar conclusions were reached by astronomers who found unexpectedly large black holes lurking in the early universe.
In the next steps for this research, Simon intends to investigate black holes that are located even further away from Earth and thus can be seen even earlier in cosmic history. He hopes that this investigation could help reveal how galaxies like the Milky Way form, because supermassive black holes exert enormous influence on the galaxies that host them.
“Understanding the mass of black holes is critical to some of these fundamental questions such as the gravitational wave background, but also how galaxies grow and how our universe evolved,” he concluded.
The research was published in the May 30 edition of the The Astrophysical Journal Letters.
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