I’ve already explained how black holes suck up everything, including light. You’d expect them to grow forever. However, that’s not what happens…
I’ve already written a longer explanation of black holes, see the link above. Just to recap: black holes form when a large enough star collapses. The collapsing mass is large enough to create a singularity, a point in timespace where the solution to the Lorentz factor shoots to infinity, meaning time stands still.
Black holes often form the massive cores of galaxies, sucking in the light of surrounding stars, and generally eating the universe. Time and space matter little inside them and nothing can survive passing the event horizon.
Or maybe it’s a little more complicated…
Stephen Hawking is widely known for his ‘a brief history of time’. He is also famous for discovering something we Hawking radiation.
Before we move on to the actual Hawking radiation, we have to talk about virtual particles. Quantum mechanics is a weird field of science. It predicts things that we mere humans have trouble wrapping our minds around. Most people will have heard of the Schrödinger cat, for example, but few actually understand what it means. And I still can’t wrap my head around why the theory of relativity says faster than light travel implies time travel.
One part of quantum mechanics that is baffling is the use of virtual particles. In certain interactions in quantum mechanics, you need virtual particles to explain what happens. These particles are usually a particle and its anti-particle that spring into existence for brief periods time and then vanish again. In the interim, they have real-world effects.
Virtual particles have been extensively verified. That doesn’t mean we completely understand them. The idea of particles popping into and out of existence at random is disturbing, and hard to fathom. Quantum mechanics and/or general relativity are known to be incomplete, as they conflict with each other, so maybe some better explanation will one day be found. However, for now, only virtual particles can explain some of the effects we are seeing.
Imagine a black hole. It’s in vacuum, sucking in everything under and including the sun. Also imagine virtual particles popping up all over the place and vanishing. These virtual particles are a matching matter and anti-matter particle.
Now imagine that every so often, a pair of virtual particles pop up, but before they can vanish again, the anti-particle falls into the black hole and passes the event horizon, and the virtual particle doesn’t. Oh dear, now our pair of virtual particles has lost one of its pair. The other particle sighs and scoots off on its own, becoming a real particle.
These escaping particles are known as Hawking radiation. The resulting radiation is very weak, but it does exist. Not only that, the process actually takes some energy from the black hole.
Black hole evaporation
Hawking radiation will transmit tiny amounts of energy away from a black hole. Over time, if no new matter falls in, the black hole will shrink. Little by little, the entire black hole will evaporate.
The amount of radiation is dependent on the size of the black hole. Microscopic back holes will evaporate in an instant, while super-massive black holes at the hearts of galaxies will outlive us mortals, our planet, and even our sun.
And you thought black holes would eventually suck up the universe.
Guess again. The universe is too large for this, and the black holes will slowly vanish. Eventually, all the galaxies in the universe will go out, and the black holes will evaporate, and then all space will be a dark cold void.
At least, that’s what our science says at the moment.