A closer look at Black Holes
Black Holes in general relativity
Not long after the theory of relativity was published physics theorists realized that it predicted something so profoundly troubling many believed it couldn't exist in the real world. Anything very heavy and very small would create such strong gravitational field that space and time would be bent and twisted to breaking point. General relativity had predicted the existence of black holes.
Both physics and mathematics failed to fully explain the concept of a black hole. Einstein himself started believing that black holes could never physically form and that Mother Nature had some sort of mechanism that would stop them from being produced. In 1939 he wrote a paper explaining his new theory, although soon after being published the paper was proven wrong. Theory of black holes continued to boggle physics minds.
Black hole myths
- Black holes have become an essential part of the mythology of the cosmos, featuring as the dark, all-consuming spirits of space. But like most myths, though, you can't believe everything you've heard about black holes. Firstly, they may not even exist. Einstein's general relativity predicts that they can form, and we have very good indirect evidence for them, but in principle they might not be real. The evidence could be produced by some other phenomenon.
- Then there's the idea they're kind of universal vacuum cleaner, sucking up everything and anything that dares to come near and that their gravitational pull is unimaginably strong - thousands time stronger than the star's the black hole formed from. Actually, if you were in orbit around a star when it collapsed into a black hole, you would continue to happily orbit around it without being pulled in. In other words, gravitational pull doesn't change when star becomes a black hole. But what does change is the concentration of mass - black hole has the same mass as the star before, but it is concentrated in a point that is theoretically zero size. Because of that you can come much closer to that mass. And only then you'll start to feel the ruthless gravitational pull.
- The last myth is not about the black hole itself but about the first man to create a concept of it. In most cases people think that either Albert Einstein or Stephen Hawking were the first men to do it. Surprisingly, it was John Michell who, in a 1783 paper first proposed the idea that there were such things as black holes, which he called “dark stars.” Having accepted Newton’s corpuscular theory of light, which posted that light consists of minuscule particles, he reasoned that such particles, when emanated by a star, would be slowed down by its gravitational pull. He then thought that a star’s gravitational pull might be so strong that the escape velocity would exceed the speed of light. Since light would not be able to escape such a star, it would be invisible.
Building a black hole
Black holes are born when nature's most massive stars burn off all their fuel and violently collapse. The phenomenon of a dying star is called a supernova. During super nova, star with the mass of our sun shrinks to something that's probably about the size of planet Earth in a fraction of a second. It continues shrinking to a single point called singularity. Singularity, though said to be of a zero size, theoretically can't be smaller than a Planck area (Planck length squared).
All black holes have their own event horizon which is the point of no return - after you passed it through, gravitational force will be pulling you towards the singularity so fast, that you'll be moving faster than the speed of light. That’s why even light can't escape beyond that point.
Journey inside a black hole
Imagine being in a space suit, heading for the black hole feet first. Your feet would feel a much stronger attraction than your head. The difference in a pull across the length of your body would stretch you so much that you would end up like a long, thin piece of pink spaghetti. This process is known as spaghettification (despite rumors, scientists do sometimes have a sense of humor).
Black hole warping space and time
What's so special about singularity ?
Center of a black hole, called a singularity, is in theory a point. But, technically, it is not a point in space, it is a point in time! General relativity says that gravity is a warp in space and time. At the heart of a black hole time itself is well and truly twisted. Once you pass through the event horizon you are headed for a point in time, not a point in space. The time of you total obliteration is fixed at that moment...
Also, approaching my final paragraph, I could say that very long time ago everything you saw, see or will see once was a singularity.
Why are black holes important ?
- Center of a black hole - singularity - is a point. A point that is very complicated and troubling for all the astronomers that are working with it. Nevertheless they continue struggling to find out more about this phenomenon. But why, you ask? Well, it is well known that our universe is constantly expanding since its formation. But that also means that billions of years ago, our universe was also a single point - singularity. If we somehow managed to learn more properties of black hole's singularities, we might also know more about the universe itself...
- Very massive objects, like planets or stars, tend to warp space and time. Black hole is ridiculous mass concentrated in a zero size point. In theory that point has infinite density. Because of that space and time might not only be warped but also affected in some other ways. Nothing that crosses event horizon can get out of the black hole. But it might get out of it yesterday. Or tomorrow. Basically the object could be transported to a different timeline via 5th dimension (parallel universes). Of course nobody knows if none of this is true but for now black holes are the only scientifically possible ways to time travel.
- Most of galaxies known to humans have enormous size black holes inside them. But the most interesting thing is that there is a positive correlation between mass of the black hole and mass of the galaxy around it. What this actually means is that the black hole somehow determines the mass of the galaxy and even number of stars inside it. If you want to visualize - black hole to galaxy around it is like a grape to planet Earth, but somehow this grape can control something millions of times bigger...
Black holes deadly environment
Black Holes will eventually die
We live at a time in which most of the energy of our universe is produced by stars. Trillions of years from now all across the universe stars will begin to use up their fuel and fade away. The largest stars fall to towards the centers of galaxies where they are swallowed by supermassive black holes. As the universe decays it gives way to a long era dominated by dying stars and black holes. Eventually these black holes merge together to farm even bigger black holes. Pretty much all matter eventually will fall in these black holes and they will become the last what has left from our universe. Now if Stephen Hawking is right, all black holes emit heat radiation - they constantly lose enormous quantities of energy. This means when they are left without any matter to absorb they will decay enough energy to explode. When the last black hole explodes - it will be the end of our universe.
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