FAQs- Black holes

What exactly are Black holes?
I get that a question a lot. People think that black holes are something out of science fiction, a region of nothingness, often embodying a wormhole (a tunnel-like connection between two distant points in space), etc. etc.

The truth is far less glamorous. If anyone want the professional and expert definition of a black hole, look it up on wikipedia. However, be warned that some of it may fly far above your head. This post has a brief description for kiddies.

A black is not science fiction. It is perfectly true, and a surprisingly common phenomenon. It is the wormhole part which is sci-fi. There cannot be any 'quantum' connection of any sort between two points in the Universe. The term quantum itself is misleading, like when people use high-funda terms to make it look as if they know something when actually they know squat!

Anyways, back to the topic.

A black hole is sort of an afterlife for a big star having at least 1.44 solar masses (for non-rotating bodies), or 24 solar masses (otherwise). When a star finishes its life cycle, the outer layers expand in a very large cosmic explosion, called a supernova. The core, however, retains all of the original gravity of the star, and collapses in on itself. This collapse is very rapid, and squeezes all the mass into a point that is ver small in diameter. At this point, the density is very high, and so is the gravitational force of the body. The force is so great, that even light can't escape the event horizon, and gets trapped inside. This body appears invisible (no light reflected off its surface reaches us), and so is known as a black hole.

If a Black Hole is invisible, how can we see it?
Simply by observing how visible matter interacts with it. Around a black hole, matter from nearby bodies (or stars, as in a binary system) gets accreted around it. All this matter forms a sort of disc (similar to Saturn's rings) called the accretion disc rotating at high speed. Also, at the poles along a black hole's rotationary axis, two beams of high energy X-rays are emitted. These are called jet streams. As a black hole rotates, these jet streams swing around. So if we see an hourglass pattern of X-rays in space with nothing at the centre, we know it's a black hole.

Another interesting thing is that black holes often act as giant cosmic lenses. If there's a black hole in the foreground with a band of stars in the back, by observing the motion of the band of stars, we can see if there's a black hole. The light is refracted and bent along the event horizon, giving it the appearance of a lens.

Here's another funny method. You know how kids play ring-a-roses? They just keep revolving around nothing in particular. By observing similar behaviour in nebula clouds, or in planets, we can guess at the location of a black hole. This is easier than it seems because of the absence of light from a black hole.

What will happen if you fall in a black hole?
Interesting question. Astrophysicists get that a lot. The phenomenon of falling into a black hole can be described by a term - 'spaghettification'. As hilarious as it sounds, that is probably very accurate in describing the effect.

If you stand on any body with mass, your feet, which are closer to the ground, experience more gravity than your head, which is farther away. Since gravity is a very weak force, on large planets, you won't feel the difference. But on a black hole, the radius is so tiny, that the difference will be very large. So your body will begin to stretch along the middle as you get closer. The lower portion of your body will fall faster than the upper part of your body, stretching it even more. Eventually, you'll be ripped into two. This will continue with the rest of your body (2, then 4, then eight parts) untill your reduced to atoms, and sucked down the even horizon. Funnily enough, you won't feel a thing, because you'll be long dead by then, crushed by the gravitational force way high up in orbit. Not very comforting, so don't try sky diving into one anytime soon!

What are wormholes?
Ah, finally the topic of Wormholes!
Well, theoretically, wormholes are possible. But practically, it's a long shot. According to Einstein's equations, space time is a sort of cloth on which galaxies and stuff are embroidered. Now, you could fold this cloth back upon itself. If you pass a needle (with a thread) through the two layers of cloth, passing through one end, out through the other), then this would represent a wormhole. It is an inter-dimensional tunnel connecting two distant points to each other via a shortcut.

Here, all the laws of physics would break down. All particles would revert to sub-atomic state (proton, neutron, electron) and out of the other end it would reassemble. The reassembling is the tricky part.

According to equations, they're allowed. But you know how equations are very annoying? Take for example, while solving a quadratic equation for area, you get two values; one positive, one negative. The negative one is obviously wrong, so you convert it to modulus of its form, blah blah blah... Practically, negative area is crap!

Similarly here. Mathematics can get you all sorts of crazy stuff. We logicians are given the heavy duty of sifting what is possible from what is crap. Logically, creation of such a region is filled with paradoxes. And nature doesn't take paradoxes too well. Two solution? Get out! It's a bit like that with the Universe.

Since I don't really entertain the idea of an inter-dimensional passageway, I didn't bother to research this topic. But if you sincerely wanna know, I can look it up for you.

What are singularities?
Singularities are related to black holes, but quite distantly. Singularities are factors with the denominator zero, or very close to zero. This gives the quantity the potential to go very near infinite. It's sort of like zooming in on a point. You can go in forever and ever, but it'll never get larger, because it has no dimensions. It's a place where all physical lines meet, and go no further.

Black holes are not exactly singularities because their radius (in this case, the radius is the denominator) are not quite zero.

More Questions and Answers in the next blog...