Black holes are some of the most mysterious and fascinating objects in the universe. These are objects whose gravitational pull is so intense that nothing, not even light can escape once it enters a region at the boundary of the black hole known as event horizon. Once anything crosses the event horizon there is no force in the universe that can help it from falling inside the black hole. There are mainly three kinds of black holes. The smallest known black holes are ‘Primordial black holes’- that are thought to have formed in the early universe, the medium sized black holes known as ‘Stellar black holes’- that are formed when the center of a big star collapses and then there are the largest known black holes called the ‘Supermassive black holes’ that were formed at the same time as the galaxies they reside in.
Black holes by themselves have been a field of research for decades. People are down to Black holes because of their mysterious nature. There are a few things about black holes that make them unique and so mysterious.
- Black holes are powerful engines of nature
Black holes are probably the most efficient and powerful engine in the universe. Much of matter swirling into a black hole doesn’t fall in but is spit out outward at speeds close to the speed of light. These giant jets of matter have been observed to shoot out from Galaxies core. Giant spinning black holes are the only powerful known source that can produce such jets. This happens because some of the materials that don’t reach the event horizon get trapped in the Black hole’s powerful magnetic field. These jets of materials shooting out of the black hole emit huge amounts of energy.
- There is a Black hole at the center of our Milky way Galaxy
Yes, like most galaxies, there is a supermassive black hole at the center of our own Milky Way galaxy. The black hole, known as Sagittarius A has a mass of about four million times the mass of our Sun.
The image in the figure shows X-ray in blue color taken from Chandra X-ray observatory and infrared emissions are shown in red and yellow taken from Hubble Space telescope. The zoomed in view shows the black hole in X-rays.
- Black holes slows down time
According to Einstein’s theory, if you get closer to any massive body, times slows down. This effect can be observed on earth only by using very sensitive instruments because earth’s gravity is too weak to show any noticeable effect.
But since black holes are so dense and the gravitational pull is so strong that it literally distorts space-time. And that’s why near a black hole the slowing of time is extreme. If you can manage to orbit near the event horizon of a black hole for a while and then turn your spaceship round and fly back to earth – you will have travelled to the future! Depending on how long you stayed in orbit, you will find most people you knew are older or probably not alive!
- Trip to a black hole is a one way trip
The extreme gravitational pull of a black hole makes it impossible for anyone or anything to escape from it once it has crossed a certain region called the event horizon. Not even light can escape from this gravitational pull. You may be able to survive a trip (well at least for a while) through the event horizon of a supermassive black hole. But for a stellar mass black hole tidal forces are large even outside the event horizon. And so you will be ripped apart before you try to cross the horizon. In any case, once you cross the event horizon there is no turning back.
- Inside a black hole
So what’s inside this black hole? Well, that’s still a mystery.
Our understanding of laws of physics breaks down at the center of the black hole. A singularity lies at the center; it’s a point that contains infinite mass in an infinitely small amount of space. Einstein’s theory suggests that time is destroyed at the center, i.e. time as we know it ends there. We don’t know why time would come to end at the center of the black hole.
- If you fall into a black hole you will be spagettified
Lets say you survive your trip long enough inside the event horizon of a supermassive black hole. At first you will experience weightlessness i.e. you will be in a state of free fall. But as get closer to the center of the black hole you will start to feel tidal ‘stretching’, meaning if you legs would feel a much stronger pull than your head as it is closer to the center. You will experience this extreme stretching until you are ripped apart or spagettified. For a stellar mass black hole you will experience this even before you cross the event horizon.
- Black holes evaporate
Black holes do evaporate although we are not entirely sure how. Stephen Hawking showed in 1974 that black holes are not entirely black, they do emit radiation and as a result black hole shrink. Eventually they will vanish completely. And this process is known as black hole evaporation. However, this is a very slow process and some of the very small primordial black holes evaporate over long periods of time and massive black holes can live for billions of years.
- Black holes do not suck or at least not if you keep your distance
A very common misconception about black hole is that many people think black holes suck everything around them. Yes, they are undoubtedly very weird objects in space but they definitely do not suck things into them like a monster. As long as you keep a safe distance from the event horizon you are safe like any other place in space. In fact, the black holes gravitational field is the same as any other object of the same mass.
- Universe inside a Black hole
Some scientists claim that inside a black hole there is one-way door between two universes. If somehow you manage to survive a trip through the center black hole of our Milky Way galaxy, you may end up in another universe. If that’s true, then we might be living inside a black hole right now. It can be hard to believe at first, but it may actually be the best explanation of how our universe came into existence. Unfortunately, there is no way to do a direct experiment to prove this theory since no information can get back out of a black hole. The only thing we can do is to study black holes from outside and develop theories about what lies inside a black hole.
- Its possible to see a black hole form
Yes! It is possible to see the beginning of its formation of stellar black holes. Stellar black holes form when the center of a massive star collapses in upon itself. This causes the star to explode and huge amount of energy is released during this process emitting a flash of gamma rays. This happens when a star goes supernova. This is the last view of the stars core that can be detected using telescopes before it collapses into a black hole. Telescopes can detect the fading of the dying star and the formation of a black hole.
If you would like to know more about black holes, there are many books out there. My personal favourite is Kip Thorne’s Black Holes and Time Warps: Einstein’s Outrageous Legacy, if you are interested.
Do you know of any other mind-blowing facts about black holes? Then share your knowledge in the comments below.