Sunday Space: the anatomy of a black hole

The black hole in the centre of the image is the ... black hole! The yellow donut shape is the gas and dust from stars and the galaxy spinning around the black hole, which will eventually fall into it. The swirly lines are polarised light (similar to how many sunglasses work), spiralling around, which is due to the very strong magnetism of the black hole.

This makes people wonder if nothing, not even light, can escape a black hole, how can you see a black hole?

Firstly, they are not holes - they are real, physical objects that are round and spinning.

When most people think of black hole, they think of the singularity - the very centre. However, there are lots of parts to the black hole and we need to understand their anatomy.

The singularity, the centre of the black hole, is an area in space where the gravity is so strong, nothing, not even light, can escape. It is an area where a massive amount of matter has been squeezed together, and where you have mass, you have gravity. And the more mass, the more gravitational pull it has.

The boundary of the singularity is called the event horizon - beyond this limit, the gravitational pull is so strong, not even light can escape. Further out, there is the limit where an object can orbit around the black hole without necessarily falling in - the innermost stable orbit. As you get further way, the force of gravity decreases, like all objects.

This is the reason why the sun isn't pulling us humans off of Earth. The sun is about 333,000 times more massive than the Earth, but also 150 million kilometres away, so its gravitational pull on us is much weaker than Earth's.

As stars and gas approach the black hole, they slowly get stretched and ripped apart - in a process we call spaghettification. As stars, planets, and other objects get ripped apart and fed on by the black hole, bits of material get flung around.

Since the black hole is spinning, this gas and dust spins in a disc around the black hole - for the same reason bits of rock and ice spin in a ring around Saturn. The gas and material around the black hole gets heated and glows, which is what we see - called the accretion disk. Not all black holes have this, so we can't see all black holes this way.

Some of the bits of eaten stars get shot out, in huge jets approaching the speed of light. Since the black hole is spinning, some of the old star stuff almost bounces off the black hole, and gets shot out perpendicular to the direction the black hole is spinning, out the top and bottom, or the poles of the objects.

Black holes may be a bit more complex than we usually give them credit for, but they definitely are amazing objects in the universe.