Astronomers refer to a massive object known as Sagittarius A* as being located close to the Milky Way Galaxy’s center. It’s possible that our galaxy and this “supermassive” black hole grew together. Similar behemoths may be present in the center of nearly all massive galaxies in the universe, according to scientists.
According to Joseph Simon, a postdoctoral researcher at the University of Colorado Boulder’s Department of Astrophysical and Planetary Science, some can grow to enormous sizes.
“The black hole at the center of our galaxy is millions of times the mass of the sun, but we also see others that we think are billions of times the mass of the sun,” he said.
The astrophysicist has devoted his professional life to researching the behavior of these challenging items. He used computer simulations, or “models,” in a recent study to estimate the masses of the greatest supermassive black holes in the universe using a mathematical concept called the black hole mass function.
In other words, Simon sought to determine what you might find if you could put each of these black holes one by one on a humongous scale.
His findings indicate that black holes may have been significantly larger than previously thought billions of years ago. The discoveries may shed light on an even greater mystery, explaining the processes that molded things like Sagittarius A* as they evolved from tiny black holes into the enormous objects they are now.
Understanding the masses of black holes is critical to some of these foundational questions like the gravitational wave background, but also how galaxies grow and how our universe has evolved.
Joseph Simon
“We’re starting to see from a variety of different sources that there have been pretty massive things in the universe since pretty early on,” Simon said.
He published his findings May 30 in The Astrophysical Journal Letters.
Galactic symphony
For Simon, those “pretty massive things” are his bread and butter.
The astrophysicist is part of a second research effort called the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Simon and hundreds of other researchers from the US and Canada have been working on the project for 15 years in an effort to find a phenomena called the “gravitational wave background.”
The idea relates to the regular flow of gravitational waves, or enormous space-time ripples, that oscillate through the universe on a nearly continual basis.
This cosmic churn also owes its origins to supermassive black holes. Simon said that the center black holes of two galaxies may collide or even merge if they encounter one other in space. They spin endlessly around one another before colliding like two cymbals in an orchestra, but this collision produces gravitational waves, which physically alter the fabric of space and time.
However, in order to comprehend the gravitational wave backdrop, astronomers must first determine the precise mass of the supermassive black holes in the universe. Bigger cymbals, Simon said, “make a bigger bang and produce much larger gravitational waves.”
There’s just one problem.
“We have really good measurements for the masses of the supermassive black holes for our own galaxy and for galaxies close by,” he said. “We don’t have those same kinds of measurements for galaxies farther away. We just have to guess.”
Black holes on the rise
In his new research, Simon decided to guess in a whole new way.
First, he gathered information about hundreds of thousands of galaxies, some billions of years old. (Light can only travel so fast, so when humans observe galaxies that are farther away, they’re looking back in time).
With the aid of this knowledge, Simon was able to estimate the black hole masses of the universe’s greatest galaxies. The gravitational wave backdrop those galaxies might produce and that currently covers Earth was then simulated using computer models.
According to Simon’s findings, the cosmos has a full assortment of supermassive black holes that date back about 4 billion years. He also noticed something odd: There seemed to be a lot more large galaxies spread throughout the universe billions of years ago than some previous studies have predicted. That didn’t make much sense.
“There’s been the expectation that you would only see these really massive systems in the nearby universe,” Simon said. “It takes time for black holes to grow.”
His research, however, adds to a growing body of evidence suggesting that they might not need as much time as astrophysicists once believed. The NANOGrav team, for example, has seen similar hints of giant black holes hiding in the universe billions of years ago.
For the time being, Simon wants to investigate all of the black holes that reach even further into the past in order to find out how the Milky Way Galaxy and eventually our own solar system came into being.
“Understanding the masses of black holes is critical to some of these foundational questions like the gravitational wave background, but also how galaxies grow and how our universe has evolved,” Simon said.
