What is Black Hole ?

John Michell (1783) and Pierre-Simon Laplace (1796) were the first people to propose the concept of “dark stars” or object which, if compressed into a small enough radius, would have an escape velocity which exceeded even the speed of light. Later, the term “frozen star” was used to describe the last phase of a star’s gravitational collapse, when light unable to escape from its surface would make the star appear frozen in time to an observer.

As your feet begin to get stretched by gravity's pull, they will become increasingly more attracted as they inch closer to the centre of the black hole. The closer they get, the faster they move. But the top half of your body is farther away and so is not moving toward the centre as fast. The result: spaghettification!

Physicists now believe that black holes actually radiate small numbers of mainly photon particles and so can lose mass, shrink then ultimately vanish over time. This unverified evaporation process is known as “Hawking Radiation”, after Professor Stephen Hawking who theorized its existence in 1974

It might sound crazy that black holes could spawn new universes – especially since we're not sure other universes exist – but the theory behind this is an active field of research today.

It is now thought that most galaxies are held together by supermassive black holes at their centers, which cluster hundreds of solar systems around them. In fact, 30,000 light years away at the centre of our own Milky Way galaxy is a black hole with 30 million times the mass of our own sun.

A very simplified version of how this works is that our Universe today, when you look at the numbers, has some extremely convenient conditions that came together to create life. If you tweaked these conditions by even a miniscule amount, then we wouldn't be here.

The singularity at the centre of black holes breaks down our standard laws of physics and could, in theory, change these conditions and spawn a new, slightly altered universe.

Black holes are one of the most interesting parts of astronomy to learn about! Here are some fun facts to answer any questions you might have about black holes.

The way this works has to do with the disk of material that orbits around a black hole. The material that is nearest to the fringe of the event horizon on the inner edge of the disk will orbit much more quickly than material at the very outer edge of the disk. This is because the gravitational pull is stronger near the event horizon.

A black hole appears black because its gravitational pull is so strong that not even light can escape. It also acts like a hole because things around it, like stars, “fall” into it. Therefore, it is called a black hole.

To compare, nuclear fusion converts about 0.7 percent of mass into energy. The condition around a black hole converts 10 percent of mass into energy. That's a big difference!

Yes! The “point of no return” is the place where the gravitational force in the black hole is too strong to overcome. This point is called the “event horizon.” If something gets past the event horizon there is no way it can escape.

Scientists have even proposed that this kind of energy could be used to power black hole starships of the future.

Scientists believe there is be a supermassive black hole at the centre of nearly every galaxy – including our own. These black holes actually anchor galaxies, holding them together in the space.

While it’s very very unlikely you will ever encounter a black hole, it’s fun to wonder about what would happen if you did. It certainly would not be a fun experience! Watch this video to learn a little bit about what might happen if you fell into a black hole:

Since a black hole doesn’t emit any light, it’s impossible to actually see it. Instead, scientists discover black holes based on how the things around it act. For example, they might notice that a star is losing lots of mass. That is because a nearby black hole is sucking in part of the star!

The black hole at the centre of the Milky Way, Sagittarius A, is more than four million times more massive then our sun. Although the black hole, which is almost 30,000 light years away, is pretty dormant at the moment, scientists believe that 2 million years ago it erupted in an explosion that may have even been visible from Earth.

As you reach the event horizon, you are moving at such high speeds due to the strong gravitational force from the black hole, that time will slow down.

Hawking radiation disperses a black hole's mass into space and over time, and will actually do this until there is nothing left, essentially killing the black hole. This is why Hawking radiation is also known as black hole evaporation.

The only difference between a black hole and our Sun is that the centre of a black hole is made of extremely dense material, which gives the black hole a strong gravitational field. It's that gravitational field that can trap everything, including light, which is why we can't see black holes.

If you shrunk our Sun down to a size of only 3.7 miles (6 km) across, for example, then you would have compressed all of the mass in our sun down to an incredibly small space, making it extremely dense and also making a black hole. You could apply the same theory to Earth or to your own body.

But in reality, we only know of one way that can produce a black hole: the gravitational collapse of an extremely massive star that's 20 to 30 times more massive than our Sun.