WHAT IS A BLACK HOLE?
Black hole is a region where gravity is so strong that even light cannot escape from it. Since nothing can travel faster than light, everything else gets dragged into black hole too.
The edge of a black hole is called the ‘horizon’. It is like the edge of waterfall. If you are above the edge, you can get away if you paddle fast enough, but once you pass the edge, you are doomed.
As more things fall into a black hole, it gets bigger and the horizon moves further out.
HOW IS BLACK HOLE MADE?
To make a black hole you need to squash a very large amount of matter into a very small space. Kind of like, filling a jam jar with matter equals to the size of earth. The gravitational pull will be so strong that light will be dragged back, unable to escape.
One way black holes are formed is when stars that have burned up their fuel explode like giant hydrogen bombs called supernova. The explosion will drive off the outer layers of star and the central region will be pushed inwards.
Much larger black holes are formed inside clusters and center of galaxies containing smaller black holes, neutron stars and ordinary stars. Collision between black holes and other objects will produce glowing black holes which swallow everything that comes too near to it. Our own Milky way galaxy has a super massive black hole at its center, several million times the mass of Sun.
HOW DO YOU SEE A BLACK HOLE?
Well, we can’t really see a black hole. Its like, looking for a black cat inside a dark room. But we can surely detect black holes by the way its gravity pulls on other things.
If we see stars orbiting around something we can’t see, we can conclude that it is orbiting around a black hole. Or if we see discs of gas or dust rotating around a central object which we can’t see, we know it can only be a black hole.
FALLING INTO A BLACK HOLE
If you fall in feet first, your feet will be nearer to the black hole than your head and will be pulled harder by gravity. So you will be stretched out lengthwise and squashed in sideways. So you will be torn apart and made into a spaghetti if the black hole is only few tomes the mass of sun.
But if the black hole if much bigger, you will pass the horizon of black hole without even noticing anything. However, someone watching you fall from a distance will never see you cross the horizon because gravity warps space and time near a black hole. To them you will appear to slow down as you approach the horizon and get dimmer and dimmer. You get dimmer since because the light you send back takes longer time to get away from black hole.
GETTING OUT OF A BLACK HOLE
Well people think that black holes are the ultimate prison since there is no way to get out of it. Anything that fell into it is gone forever. But this is not quite right. Tiny fluctuations in space and time mean that black holes are not perfect traps. It slowly leaks particles. This is known as Hawking’s Radiation. Smaller black holes evaporate faster compared to larger ones. The rate of evaporation is very slow at first, but then speeds up as the size of black hole gets smaller. Eventually after billions and billions of years, the black hole will disappear.
But what about the prisoners in the black hole? Well, they will be recycled into energy and particles. If we examine what comes out of a black hole, we can reconstruct what was inside. So the memory of what falls into a black hole is not lost forever, just for a long time.