- A black hole is an object in space that is so dense and has such strong gravity that no matter or light can escape its pull. Because no light can escape, it is black and invisible. There’s a boundary at the edge of a black hole called the event horizon, which is the point of no return — any light or matter that crosses that boundary is sucked into the black-holes. It would need to travel faster than the speed of light to escape, which is impossible.
- Anything that crosses the event horizon is destined to fall to the very centre of the black hole and be squished into a single point with infinite density, called the singularity.
Size of black holes:
Small black-holes are called stellar-mass black-holes. They have masses similar to those of larger stars — about five to 20 times the mass of the sun. The other kind is supermassive black-holes, which are millions to billions of times more massive than the sun. That’s the kind the Event Horizon Telescope has been trying to photograph, as bigger objects ought to be easier to see. There is some evidence that black-holes between these two sizes exist, but that has yet to be confirmed.
While black-holes are very massive, that doesn’t mean they take up a lot of space. Because they’re so dense, they’re actually quite small. According to NASA, a black hole 20 times the mass of the sun could fit inside a ball 16 kilometers wide — the width of the Island of Montreal at its widest point.
Location of black holes:
- Super massive black-holes are found at the centre of most galaxies, including our own Milky Way. The one in our galaxy is called Sagittarius A* and is one of those the Event Horizon Telescope has been attempting to photograph.
- Sagittarius A* isn’t the only black hole in our galaxy, though. Earlier this year, astronomers discovered another 12 within three light-years of it, suggesting there could be upwards of 10,000 black-holes around the galactic centre.
Origin of black holes:
- Super massive black-holes are believed to form at the same time as the galaxy that surrounds them, but astronomers aren’t sure exactly how.
- Stellar mass black-holes form when a star with a mass greater than three times that of our sun runs out of fuel. It explodes into a supernova and collapses into an extremely dense core that we know as a black hole — something predicted by Albert Einstein’s general theory of relativity.
- Einstein’s theory also predicts the size and shape of the black-holes that the Event Horizon Telescope is trying to photograph.
There is a region of space beyond the black hole called the event horizon. This is a “point of no return”, beyond which it is impossible to escape the gravitational effects of the black hole.
Event Horizon Telescope Project:
EHT is a group of 8 radio telescopes (used to detect radio waves from space) located in different parts of the world.