The Extremes of the Universe – and how we can use them

Rohan Katkar

Today, we hear the words ‘million’ and billion’ thrown around a lot. Bernard Arnault (the richest person in the world at the time of writing) has a net worth of 218.3 billion USD. One million years ago, the first human-like creature (hominid) set foot in the UK. Your friend might say, ‘I beat those guys a billion times.’ However, few of us can comprehend what those numbers really mean. We understand that a million, billion and trillion are massive, but in a world where they are used every day, we don’t see the difference between them. For most of us, a billion atoms mean the same thing as a trillion atoms.

But to get a true understanding of our world, we should sometimes take the time to get our heads around how significant these numbers really are. And nowhere is this more the case than when learning about the true extremes of the universe: black holes, the most massive objects in existence.

What is a black hole and how are they formed?

Put simply, a black hole is a region of space where nothing, not even light or other electromagnetic waves have the energy to escape it due to its immense gravity. To get out of a black hole once past its event horizon (you can think of it as the point of no return) you would have to travel faster than the speed of light, which is against the laws of physics. There are no other objects in the universe which have this property.

There are two ways a black hole can form: through a supernova and a kilonova. Let’s explore both.

Supernovas are the most extreme explosions in the universe, occurring when supermassive stars implode due to gravity at the end of their lives. Their iron cores are crushed as their immense mass (1.9891 x 10^31 kg) rushes towards them at 25% the speed of light (which would be 75,000 km/s), forcing them into spaces so small that they become black holes.

The same thing happens during a kilonova explosion. This is when two neutron stars collide, and these are the densest objects in the Universe. By the same principle, gravity crushes the matter during the collision, forcing it into a small enough space to become a black hole.

How big can black holes get?

Black holes exist in all sizes. There are those the size of a proton with the mass of a mountain; then there is V723 Mon, 24 times the mass of the Sun, but only 17.2 km (about 10.69 mi) wide; and Sagittarius A, the monster in the middle of the Milky Way with 17 times the Sun’s radius, but 4 million times the mass.

But there are also ultra massive black holes. The largest black hole known to humans; Phoenix A has a diameter of 590 billion kilometers. That’s 590,000,000,000 km. Think about that. Even going at the universal speed limit, the speed of light, it would take nearly a month to cover that distance. For comparison, Pluto is only 5 hours away at this speed.

How can we use black holes?

It's time to get into some weird science.

Consider this. You know that the Earth spins on its axis – that's why we have day and night. In the same way, stars also spin on their axes. Since most black holes are formed from stars, they are also spinning, very, very fast. Black holes have such gravity, that they literally drag space-time (it can be thought of as the fabric of the

universe) along with them. This creates a region of space called the ergosphere, and it is necessary to move faster than light to stand still here. Clearly, there is a lot of energy here, and this is the secret – we steal it.

We use a mirror that completely envelops the black hole, without being pulled in itself. Obviously, this mirror would have to be quite large. However, an advanced future civilization would not find this much of a challenge - the metal from a large asteroid would suffice.

Once this is done. We open a window in the mirror and shoot electromagnetic waves into it. A large amount of these shoot through the ergosphere, where they gain a huge amount of the black hole’s rotational energy. They bounce between the black hole and mirror, getting stronger each time. If we do not release them, we will have the most powerful bomb ever created – the mirror will explode. Once released, however, we can harness this energy, gaining enough to create a civilization lasting trillions of years.

Conclusion

The last paragraph may have sounded like science fiction, but it is very possible – we just don’t have the resources to do it. Black holes are extremes, without a doubt, and they will last longer than all stars in the Universe. With this in mind, the last human alive could end their life around a black hole, which sounds depressing, but shows how amazing these objects can be.

Credits

Most of the content in this article is from the ‘Kurzgesagt – In a Nutshell’ YouTube Channel. If you are interested in science, they have covered lots of fascinating topics. The videos used are listed below: The Black Hole Bomb and Black Hole Civilizations - YouTube Black Holes Explained – From Birth to Death - YouTube