What are black holes — and what would happen if I get close to one?

Children ask about black holes on an almost daily basis. They are very aware of their existence and are incredibly curious about these elusive dark objects. Here are some of our answers to the most popular questions…

1 What are black holes?

Stars much bigger and more massive than the sun eventually explode when they run out of fuel. This is called a supernova, and it’s briefly brighter than a whole galaxy of hundreds of billions of stars.

Often the explosion leaves the core of the star behind. It is very small and compact, and is called a neutron star. It is still heavier than the sun but could fit into the UK (imagine that — one million Earths could fit inside the Sun, and yet this dead star could fit into our country). They are so dense that if you took a sugarcube of material from these stars it would weigh the same as Mount Everest.

While all neutron stars continue to glow for some time, some also give off a beams of particles, similar to a lighthouse and its spinning beams of light. If the star that went supernova is really big, the core becomes so dense that its gravity is strong enough to swallow up light and anything else that falls in. These are black holes.

2 What would happen if I got close to one?

If you approached a black hole you would feel the incredibly strong gravitational pull: your feet going in would be pulled more than your head, and you would be stretched. Scientists call this effect spaghettification.

Then you would be pulled into the centre and squashed into little particles to join everything else that fell in to this cosmic death machine. However, if you sat outside the boundary of the black hole (called the event horizon) and somehow protected yourself from spaghettification, time would tick slower for you.

You wouldn’t notice this — for you time would tick at its normal rate. However, if astronomers on Earth could see your watch they would see that it was ticking slower than their watches. Strong gravity slows down time.

Let’s say you spend a year very close to the black hole and then you decide to return home. How old would you be? Well, many years may have passed on Earth, tens, hundreds, thousands or maybe even hundreds of thousands of years will have gone by without you realising.

3 Where is the nearest black hole to us?

The closest to Earth is called V616 Monocerotis, which is 3,000 light-years away. This means that if we sent a text message to this black hole it would take 3,000 years to get there, travelling at the speed of light (300,000 kilometres per second). This black hole is around 10 times heavier than the sun.

4 How many of them are there in the Milky Way?

It is thought that there are 100 million black holes in our galaxy. There are at least a thousand times as many stars as there are black holes.

The biggest black hole in the Milky Way is called Sagittarius A* and it lives in the centre of our galaxy. It is 4 million times heavier than our sun. Don’t worry though, a text message to Sagittarius A* would take 26,000 years to get there.