Black holes used to be theoretical until the first one was discovered and confirmed back in the late 20th century. Now, astronomers discover them all over the place. We even have direct radio images of two black holes, one in M87 and one in Sagittarius A* in the center of our galaxy.
So, what do we know about them? A lot. However, there is still more to learn.
A group of astronomers who used Chandra X-ray Observatory data discovered a massive supermassive black hole in a quasar embedded in a distant galaxy cluster. What they found provides clues to the origin and evolution of supermassive black holes.
Black holes' two-factor identification
There are a lot of challenges when it comes to studying a black hole, particularly a supermassive one. Every large galaxy has a central monster black hole, so it's important to know as much as we can about them. These cosmic behemoths contain millions or billions of solar masses.
They have strong gravitational pulls, and nothing, not even light, can escape their clutches. That affects our ability to observe them and their surroundings.
One thing that isn't quite clear yet: How do these monsters form and evolve?
The answer lies in part in two of their characteristics. "Every black hole can be defined by just two numbers: its spin and its mass," said Julia Sisk-Reynes of the University of Cambridge in the United Kingdom, who conducted a new study of a supermassive black hole some 3.6 billion years away from us.
"While that sounds fairly simple, figuring out these values for most black holes has proved to be rather difficult."
X-raying a black hole
Measuring the masses is difficult, although there are methods to do it. Measuring spin is a real challenge. Sisk-Reynes and his colleagues used Chandra X-ray Observatory data to study monster black holes.
The team examined H1821+643's central supermassive black hole engine and its spin rate, which it claims to be a whopping 30 billion times the size of the Sun. (By comparison, the Milky Way's central supermassive black hole has only 4 million solar masses.)
Why do X-rays exist? A spinning black hole dangles space around with it, and allows matter to orbit closer to it than it is possible for a non-spinning one.
Studies on the H1821+643 quasar's black hole reveal a strange rate, compared to other less massive holes that spin near the light's speed. The result for the quasar's black hole surprised the team.
"We discovered that the black hole in H1821+643 is spinning about half as fast as most black holes weighing between a million and ten million suns," said astronomer Christopher Reynolds (also of the Institute of Astronomy). "The million-dollar question is: why?"
Origin and evolution of black holes
According to co-author James Matthews (also at the Institute of Astronomy), the history of H1821+643 might hold the key to figuring out its slower spin rate.
During galaxies collisions, he hypothesizes that supermassive black holes like the one in H1821+643 likely grew through mergers with other black holes.
It's well-known that galaxy collisions build up larger galaxies over time, and so these same activities (including dwarf galaxies' collisions) are fair game as possible factors.
It's possible that this black hole's outer disk was damaged in a collision, which sent gas out in random directions during the event.
The spin rate of the black hole would be lowered by these kinds of activities, or it might be torn around in a completely different direction. That means such black holes might exhibit a variety of spin rates depending on their previous histories.
Matthews concluded that the moderate tilt for this ultramassive object is a testament to the universe's largest black holes' violent and chaotic past.
"It may also provide insights into what will happen to our galaxy's supermassive black hole billions of years in the future when the Milky Way collides with Andromeda and other galaxies."
Universe Today published this article in part as an adaptation.