The life of black holes

Slide 1:

Hi, my name is Michaela Gates, and I’ve spent the last quarter of my senior year researching and studying the physics of black holes. In this presentation I’ve compiled everything I personally think you should know about black holes, from birth all the way until their death. I hope you find it as interesting as I do :).

Slide 2:

So let’s start from the very beginning. The start of the universe beginning. Primordial black holes were theoretically formed right after the big bang in the so called “radiation dominated era. The high density of the universe in this era led to areas of gravitational collapse, which I will later explain to be a black hole. But the black holes that we usually think of come from the death of stars.

Slide 3:

There are two main life cycles of stars. This one here is the path our sun will take, and all stars of similar or smaller size. All stars are born from ambiguous gas and dust that has clustered in space. Then it turns into a protostar, where the cluster’s gravity will make it collapse onto itself and make it grow more dense and hot to become the earliest stages of a star. And over billions of years it will burn up the hydrogen in its core, expand into a red giant. It will eventually “die” and leave behind its core, otherwise known as a white dwarf. And as it reaches its end, and the white dwarf cools down, it will finally become a black dwarf.

Slide 4:

But those obviously never become black holes. Only large stars, ones with 25x the initial mass of our sun, explode when they run out fuel. Much like our sun, these stars start out as dust and gas, evolve into a protostar, but that’s where their paths diverge. These large stars are called supergiant stars, and are so large, they can fuse elements up to iron in their cores. But when the core becomes iron and there is nothing left to fuse, these stars will cause an explosion called a supernova. A supernova is so bright that it actually outshines the rest of the galaxy, which is about 200 billion stars. This creates an incredibly dense star called a neutron star, which is the core of the now gone supergiant. And finally, when the neutron star collapses, it’s gravity is so strong that it creates a black hole.

Slide 5:

So what, exactly, is a black hole? It’s essentially an incredibly deep pocket in the space time continuum. If you look at the diagram, things bend spacetime with their gravity. Just think of a black hole having so much gravity that it’s like a never-ending well in space time. Once you reach the “lip” of that well, nothing can crawl out again. Not even light can escape a black hole, and nothing is faster than the speed of light. This “lip” is officially called the event horizon. It’s the point of no return. And since light cannot escape and it sucked in by the black hole, we cannot actually see it. We “see” them by observing their surroundings.

Slide 7:

Here are the main types of classifications of black holes:

• Stellar Black Holes - originate from large stars (next slide).

• Primordial Black Holes - originate from the Big Bang period (next slide).

• Supermassive Black Holes - the centers of galaxies, they have the mass of a billion suns. It’s still not clear how they are formed, but they are a result of galactic formation.

• Miniature Black Holes - still have yet to discover one, but they would be smaller than the sun

• Classification based on rotation or no rotation

Slide 8:

According to Stephen Hawking, there is a way for matter to escape black holes. Quantum mechanical theory explains that throughout the universe, particles and their counterparts, antiparticles are constantly popping in and out of existence. They typically do not last long, because the particle and its counter particle quickly annihilate each other. But when these particles pop into existence near the edge of a black hole, it is possible for one side of the pair to fall in. The other side of the pair escapes, but without the other side of the pair to annihilate them, they continue to exist in the normal universe, which isn’t supposed to happen because they borrow matter and energy in order to exist, so this particle exists on stolen matter, so the black hole radiates energy out into the universe through hawking radiation. This is the process in which black holes shrink over time. But it’s an unfathomably slow process. But more on that later.

Slide 9:

So over time, a lot of anti-particles and particles are escaping, and stealing mass and energy from the universe. The black hole has to keep radiating its mass and energy away in order to compensate. Eventually, the black hole is going to evaporate into nothingness and destroy all the information inside. This means that the information inside the black hole is lost forever because all that’s left is the hawking radiation. This is a huge violation of what we know, that matter cannot be created or destroyed.

Slide 10:

Quantum mechanics states that you ought to be able to completely account for the path of any particle in the universe. So if you throw a pizza into a black hole, you should be able to trace how that pizza is torn apart; you should be able to see what happens to the individual atoms that constitute the crust, the cheese, etc. Quantum mechanics demand that all particles in the universe can be accounted for and information cannot be deleted. When I say information I mean anything that it has swallowed, galaxies, stars, planets. So here we have this paradox, hawking radiation destroys information, but the information cannot be destroyed. But as we know, there is no such thing as a true paradox. There is an answer out there somewhere, humans just haven’t found that answer yet. This answer could lie in a bunch of places, it could be that our understanding of hawking radiation is completely backwards, or that the information in the black hole does survive its destruction. WE don’t know anything for sure, but there are some theories.

Slide 11:

This theory is a bit outlandish, but it was strongly supported by Hawking so we thought it would be important to include it. The idea is that a rotating black hole gives birth to an entire new universe, which is accessible by a wormhole. SO what if all the information that falls into a black hole in our universe is transported through the wormhole into another universe. Technically, the mass still exists, even if we can’t interact with it.

Slide 12:

All information that goes into a black hole becomes imprinted on the Hawking radiation/ The idea is that from the point of view of an outside observer, nothing ever actually crosses the event horizon, so everything that fell in the black hole could be seen on the event horizon. Scientists still know very little about black holes, and it isn’t like we can go and take a look. As technology develops, scientists continue to search for answers. Remember, there is no such thing as a true paradox.

Slide 13:

Black holes will be that last things in the universe because everything will have already died or been consumed by a black hole. It'll take one googol year for that largest black holes to radiate away, and for everything to have died. According to Wikipedia, a googol year is the large number 10¹⁰⁰. In decimal notation, it is written as the digit 1 followed by one hundred zeroes: 10, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000. That’s an incredibly long time.

Slide 14:

The death of a black hole means that everything in the universe has already died -- or been consumed by a black hole. Now I know this sounds dark, and consuming, (hehe), black holes are the most complex and interesting things you will ever find. It’s a constant reminder that we still have so much to learn. And that’s pretty incredible.