Written by: Sakshyam Karna - 26013, Grade VIII
Posted on: 22 September, 2021
Black holes are one of the strangest things in existence. What are they? How are they made? What happens if you fall in them? Let’s find out.
Stars are an incredibly massive collection of mostly hydrogen atoms that collapsed from enormous gas clouds under its own gravity in their core. Nuclear fusion crushes hydrogen atoms into helium realising a tremendous amount of energy. This energy in the form of radiation pushes against gravity maintaining a delicate balance between those two forces. As long as there is fusion in the core a star remains stable enough. But for stars with way more mass than our own sun, the heat and pressure at the core allow them to fuse heavier elements until they reach iron. Unlike all the elements that went before (hydrogen, helium, carbon, Neon, oxygen, silicon), the fusion process that creates iron does not generate any energy. Iron builds up at the center of the star until it reaches a critical amount and the balance between radiation and gravity is suddenly broken. Then the core collapses, within a fraction of a second the star implodes. Moving at about the quarter of speed of light feeding even more mass into the core. It’s at this very moment that all the heavier elements in the universe are created, as the star dies in a supernova explosion. This produces either a neutron star, or if the star is massive enough the entire mass of the core collapses into a back hole. If you looked at the black hole, what you’d really be seeing is the event horizon. Anything that crosses the event horizon, anything that wants to escape the event horizon needs to be travelling faster than the speed of light to escape, in other words it’s impossible. So, what we see is just a big black sphere that reflects nothing. But if the event horizon is the black part, what is the “hole” part of the blackhole? Well it is called Singularity. We are not sure what it is exactly. A singularity may be infinitely dense, meaning all the mass is concentrated into a single point in space with known volume or surface, or something completely different. Right now, we just don't know. It's like a “dividing by zero” error. By the way, black holes do not suck things up like vacuum cleaners, if we were to swap the sun for an equally massive black hole, nothing much would change for earth, except that we would freeze to death, of course.
So what would happen if you were to fall in a black hole? Let's start from the beginning, the experience of time is different around black holes, for outside yousee to slow down as you approach the event horizon, so time passes slower for you. At some point you’d appear to freeze in time, slowly turn red and disappear. While from your perspective, you can watch the rest of the universe in fast forward, kind of like seeing in the future.right now we don’t know what happens next, but we think one of the two things: one you die a quick death. Black holes curve so much that once you cross the event horizon there is only one possible direction. After you cross the event horizon you can only walk ahead.it’s like being in a really tight alley that closes behind you in every step. The center of black hole is so concentrated that at some point even tiny distances of a few centimeters would mean that gravity acts with millions of times more force on different parts of your body. Your cells get torn apart, as your body stretches more and more, until you are a hot stream of plasma, one atom wide. Two,you die a very quick death, very soon after you cross the event horizon, you would hit a fire wall and be terminated instantly. Neither of these options are particularly pleasant, how soon you would die depends upon the mass of black hole. A smallerblack hole would kill you even before you enter its event horizon, while you probably could travel inside a super massive black hole for quite a while. As a rule of thumb , the further away you are from the singularity you are, the longer you live, Black holes come in different sizes. There are stellar mass black holes, with a few times the mass of the sun and the diameter of an asteroid. And then there are super massive black holes, which are found in the middle of every galaxy and have been feeding for billions of years. Currently , the largest super massive black hole known is S5 0014+81 which is 40 billion times the mass of our sun, it is 263.7 billion kilometers in diameter, which is 47 times the distance from the sun to pluto. As powerful as black holes are, they eventually evaporate through a process called hawking radiation. To understand how this works, we have to look at empty space. Empty space is not really empty, but filled with virtual particles popping into existence
