So, a black hole is a collapsed core of a very big star. Their gravity is so strong, as we know, even light can’t escape. However, black holes can collide.
In the early 20th century, Einstein predicted that gravity is a distortion of spacetime. He also predicted that massive objects moving through spacetime should generate ripples, like waves moving through the ocean.
Even if you walk, you leave tiny gravitational waves that compress and expand space around you. Nonetheless, it would need an extremely energetic event to produce waves that we can detect.
However, after hundred years, finally in February 2016 physicists announced the collision of two massive black holes. Together with the Laser Interferometer Gravitational-Wave Observatory (LIGO), they witnessed this cataclysmic event occurring more than a billion light-years away.
Once black holes come close to each other, they cannot escape each other’s gravity. Thus, they merge to become one bigger black hole. Events like this are extremely violent. Just like we explained above, they send ripples through space and we notice them here. Physicists call these ripples gravitational waves.
An artist’s impression of merging black holes, sending ripples through space. Credits: Swinburne Astronomy Productions
However, we don’t know much about these events. We have done simulations on powerful computers to replicate the event, but we still cannot fully understand it.
Explaining a collision
In the universe, we can find binary stars, monsters, many times bigger than the sun, orbiting each other. However, every star gets born, lives its life and finally die. In this case, when the two stars die, they go supernova, their core collapses, thus, they form a black hole. Now, we have two black holes orbiting around each other.
They radiate gravitational waves, which causes their orbit to decay. So, these black holes will spiral toward each other until they eventually collide. Like this, they create one of the most energetic explosions in the known universe.
An interesting fact is that this giant cataclysmic event happens completely in silent. Nothing can escape a black hole.
However, when the two black holes collide, they just create a more massive black hole. And this is the event that sends gravitational waves around the cosmos, detectable across more than a billion light-years.
Depending on their mass, there might be three types of black holes: stellar, supermassive, and miniature black holes.
As far as we know, supermassive black holes lie in the heart of every galaxy. Sagittarius A* is the location of an astronomical radio source at the center of the Milky Way. Various observations show that a supermassive black hole lives there.
Thumbnail image: Taken from a scene displayed in the documentary science television series called “How the Universe Works.”