Astronomy CosmologyJanuary 6, 2020

Black holes

Objects so massive that even light cannot escape

What is it?

Black holes are incredibly dense regions of space that exert such a massive gravitational force, even light cannot escape from them.

That’s a lot of science in one sentence.

So, let’s break the science of black holes down.

A black hole is a large amount of matter that is squashed to a tiny region of space.

Imagine fitting every piece of Lego in the world (that’s 400 billion bricks) into one brick.

That region of space would have a tremendous mass.

Let’s go back to our Lego example. If we squashed every Lego brick in the world into one brick, that’s going to be one immensely dense Lego brick. It’ll fall through the desk and have a huge gravitational field because the more mass an object has, the greater its gravitational pull.

The gravitational field of a black hole is so large that even light cannot escape its gravitational pull.

The boundary of this region where nothing can escape a black hole* is called the event horizon. In other words, if light crosses the event horizon, it won’t be seen again.

Here’s a random fact about balck holes. In the video, Red falls into a black hole. We can see he stretches out – a process called spaghettification – because the gravitational force at his feet is stronger than at his head. Here’s a more thorough explanation of what would happen if you fell into a black hole.

So what?

A black hole doesn’t look like a Lego brick or a star, or any other astronomical object out there.

We still don’t know what one looks like but in April 2019 a team of scientists managed to capture a direct picture of the event horizon.

Scientists have obtained the first image of a black hole, using Event Horizon Telescope observations of the center of the galaxy M87. The image shows a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun. Image credit: Event Horizon Telescope Collaboration.

But why do we study them in the first place? Because black holes help us test some of science’s leading theories. This includes Einstein’s predictions on gravity (a theory called general relativity), which predicts time dilates (moves slower) the closer you are to a more massive object (like a black hole).

In 2015, something called gravitational waves were also detected around two colliding black holes. These are tiny ripples in space-time and can help us “see” what’s happening in space to other objects.

Black holes could also unlock one of the biggest problems in physics. At the moment, two of our leading theories can’t work together. These are quantum theory (the science of the very small) and general relativity (dealing with gravity). They disagree because general relativity says information is destroyed when something falls into a black hole – but quantum theory says information can never be destroyed.

There are lots of different theories proposed to solve this inconsistency. If we could resolve this problem, we could unlock the mysteries of the universe.

What else?

* This statement isn’t right – we believe something could escape a black hole. Stephen Hawking demonstrated how black holes could emit particles, giving off a faint glow called Hawking radiation.

Also, did you know that black holes are incredibly common? Our galaxy alone may hold 100 million smaller black holes and most galaxies have a large black hole at their centre.

There’s a black hole at the centre of our galaxy too. It has a mass of four million Suns and it fits into a region of space that’s roughly the diameter of the orbit of Mercury (roughly 120 million km).