Mysteries of the Universe

Mysteries of the Universe

Do you know what's at the centre of our galaxy?

What lies at the very centre of our galaxy?

Clue: it's 4 million times as massive as our Sun, but fits into a space smaller than our Solar System.

Any ideas? There's only one thing that scientists know of that can be so small and yet so massive - a black hole. Black holes are one of the great mysteries of our universe. Scientists think that black holes can be smaller than an atom or a billion times more massive than our Sun.

A black hole is a place in space where the gravitational pull is so strong that not even light can get out. Their huge gravitational pull can rip stars apart. Have a look at this animation of a black hole destroying a star:

When a black hole destroys a star, it tears matter from the star's surface and drags it into orbit around the black hole. This matter gets superheated and starts to spin around the mouth of the black hole. Huge jets of radiation fire from the core of the black hole, which can be seen across the cosmos.

Black holes at the centre of galaxies with radiation emitting from them (c) NASA

Two blacks holes emitting radiation at the centre of galaxies (c) NASA

Because no light can get out, people can't see black holes - they are invisible. So how do we find them? Scientists can see how the huge gravitational pull affects the stars and gas around the black hole. They can also detect the enormous jets of radiation emitting from the centre of the black hole.

At the mouth of the black hole is the event horizon. At this point, even light can't escape the gravitational pull of the black hole.

The centre of a black hole is called the singularity. Even though we can see radiation escaping from a black hole, its centre is a mystery. What is happening there? No one knows. That's for the next generation of physicists - you - to work out.

Find a black hole! Explore the night sky with the Hubble telescope and see if you can find a black hole: http://hubblesite.org/explore_astronomy/black_holes/modules.html

Main image (c) NASA/JPL-CalTech

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