It looks like we’ve finally located some of the “missing” black holes in the universe.
A cluster of stars called IRS 13 near the center of the galaxy appears to harbor a black hole at its center. What’s more, the way these stars cluster and spin suggests that the black hole is rare — in the intermediate mass range, between those with star-like mass and those with supermassive mass.
Such intermediate-mass black holes are found extremely rarely, which is what makes IRS 13 interesting in itself… but what’s even more amazing is its location.
The black hole, located just 0.1 light-years from the galactic center, appears to be one of the building blocks that fuels the continued growth and evolution of the supermassive black hole at the heart of the Milky Way, Sagittarius A* (Sgr A*).
This is vital evidence that could help us understand how black holes grow, bridging the gap between stellar mass and supermassive black holes.
Black holes represent the evolutionary endpoint in the lifetime of a massive star, but the observed masses of these objects are puzzling.
In the stellar mass range, we have black holes that form from the collapse (and merger) of the cores of massive stars. For a black hole formed from a single star, the maximum mass is about 80 times the mass of the sun.
Supermassive black holes have a poorly defined mass range, but are generally accepted to be millions to billions of times the mass of the Sun. Anything between about 100 solar masses and 100,000 to a million solar masses is the intermediate mass range, where shockingly few objects have been found.
The reason this is so shocking is that it leaves the evolutionary path between small black holes and large black holes blank.
There is a gap in the observational statistics between stellar-mass black holes and supermassive black holes that cannot be easily explained – meaning we have little or no evidence of growth from one point to the next.
IRS 13 detected A little over 25 years agoThis star has puzzled astronomers ever since. At first, it was thought to be a single massive star. Then another massive star was discovered. binary. then Wolf-Wright stara massive star on the brink of a supernova.
It has since been identified. As a small groupBut it remains a puzzling mystery. It is so close to Sgr A* — a black hole with the mass of 4.3 million suns — that such a cluster should not be able to maintain its close structure.
A team led by astrophysicist Florian Peischer of the University of Cologne in Germany wanted to solve this mystery, so the researchers took a look at the way the stars and gas clumps in the cluster move. They expected the motion to be relatively random, but instead they found it to be quite orderly.
There are two possible explanations for this. The first is that the influence of Sgr A* is somehow changing the orbits of objects in IRS 13. But the team concluded that there must be something inside the cluster, keeping it together with gravity.
They did observations and modeling to see if they could pinpoint what it was. By tracking the group’s movements, they were able to pinpoint where the dense object might be.
At this location, they observed X-rays and a ring of ionized gas rotating at about 130 kilometers (81 miles) per second.
Then they calculated the mass of the object at the center of the ring using all of these motions. The scientists estimated the object to have a mass equivalent to about 30,000 solar masses. There’s only one thing it could be: an intermediate-mass black hole.
Future observations with newer instruments will give us more insight into this mysterious object, but for now, this cluster appears to represent an important step toward understanding black hole evolution.
“IRS 13 appears to be the building block for the growth of our central black hole SgrA*,” Bisker says.
“This fascinating star cluster has continued to surprise the scientific community since its discovery nearly twenty years ago. Initially, it was thought to be an unusually heavy star. However, thanks to high-resolution data, we can now confirm the composition of the building block with an intermediate-mass black hole at the center.”
The research was published in Astrophysical Journal.