What if two black holes meet

Now imagine a star 10 times bigger than the Sun. Now, take that star, and squeeze into an area about the size of Canberra. That is a black hole - a small one. Black holes come in three main sizes - stellar mass black holes, intermediate black holes, and supermassive black holes. Stellar mass black holes are the baby black holes, the result of exploding or rather collapsing stars about 10 to 60 times the mass of our Sun.

There could be upwards of 10 to 50 million of these black holes in our Milky Way galaxy alone. Inside a star, it is smashing elements together fusion to create heat and energy.

As it does it this, it is adding extra mass in its core. To support this extra weight, it burns more fuel, which in turn, creates more mass. At some point, a star cannot keep up this epic battle, and it starts to collapse in on itself. And it also looks like these two are about to collide. It turns out that even such gravitational giants as black holes occasionally run into each other in the seemingly vast Universe.

Are you about to see a nuclear bomb-like explosion of supersize proportions? The reality might be a little disappointing. Bear with me here, because to understand how black holes collide, you need to arm yourself with a bit of theory. Black holes come in all shapes and sizes. And, of course, the magnitude of the collision would depend on which black holes are slammed together. Stellar-mass black holes are the most common type.

They can have up to 20 solar masses, but could fit in a ball much smaller in diameter than our Sun. As they were circling around, they would begin pulling matter and gas into a vortex between them. Get comfortable, because it could take billions of years for their centers to merge. The excess energy from the collision would be expelled back into the Universe as gravitational waves. As I mentioned before, colliding black holes can change the shape of the space around them.

They do it by rippling this space with gravitational waves. Albert Einstein predicted gravitational waves over a hundred years ago. The cool thing about these waves is that they affect the distance between the Sun and the Earth. However, theorists have come up with ideas about how a black hole merger could produce a light signal by causing nearby material to radiate.

If confirmed, it would be the first known light flare from a pair of colliding black holes. That detection allowed the ZTF scientists to look for light signals from the location where the gravitational wave signal originated. These gravitational wave detectors have also spotted mergers between dense cosmic objects called neutron stars, and astronomers have identified light emissions from those collisions. The authors hypothesize that the two partner black holes, each several dozen times more massive than the Sun, were orbiting a third, supermassive black hole that is millions of times the mass of the Sun and surrounded by a disk of gas and other material.

When the two smaller black holes merged, they formed a new, larger black hole that would have experienced a kick and shot off in a random direction.

According to the new study, it may have plowed through the disk of gas, causing it to light up. So the detection by ZTF, coupled with what we can learn from the gravitational waves, opens up a new avenue to study both black hole mergers and these disks around supermassive black holes. Gravitational waves have never been directly observed.

However, they are a fundamental prediction of Einstein's theory of general relativity. Detecting them would provide an important test of our understanding of gravity. It would also provide important new insights into the physics of black holes. Large instruments capable of detecting gravitational waves from outer space have been built in recent years.