Black holes form when a massive star runs out of fuel. Gravity causes the core to collapse down to an object so dense that light itself can not escape. In the Milky Way galaxy, there are expected to be over 100 Million black holes, though of course we can’t see them. The one we can see is the supermassive black hole Sag A*, lying deep within the core of the galaxy. But how did Sag A* form? Was it from the merger of many smaller black holes? Or is there some other process forming the most enigmatic objects in the universe?
One of the amazing things about supermassive black holes are that they often exist as incredibly bright Active Galactic Nuclei (AGN). Because they are so bright, we can see them across the universe, all the way back to a time 700 Million years after the big bang. But around that time, stars were barely forming, so how could we have a supermassive black hole when the stars haven’t been around long enough to form the black holes that supposedly merged together?
The answer, might be that supermassive black holes don’t form through mergers of smaller black holes. But how?
A team of theoretical physicists has run a series of simulations where they seeded black holes within dense clumps of dark matter, representing galaxies. In most cases their seeds failed to grow very much, except for one central seed, which grew to over two million solar masses in only 2 million years. This is certainly in the realm of a supermassive black hole.
It doesn’t give any definite answers, but it does give researchers a place to look moving forward, as it opens a door to developing the right conditions without relying on smaller black holes from the outset. The universe is a bizarre place, and just when you think you’ve got it all figured out, science throws you a curve ball.
But that’s what’s exciting!