Black hole

The universe, unlike what people generally would like to believe, is not that friendly. It is filled with

bizarre and the most alien things possible. The huge masses of rocks hurling faster than the fastest train

on earth, the scorching radiations from the stars that we dont generally feel, thanks to the atmospheric

shield, and the low pressure of the space trying to burst open all your veins.

Above all there is the black hole the monster of all monsters.

Dont let the name fool you: Black hole is anything but empty space. Black holes are these terrifying

dense entities scattered over the universe that mercilessly grip on everything they can get their hands

on. They pull specks of dust, small rocks, asteroids, planets, and even gigantic stars, and dont let any of

them escape their grip. To get the sense of how strong black holes hold on to their prey, get this, even

light cant escape them once entered. Thats why they are called black holes we cannot see them.

So, how do we know they are there? We deduce them by detecting their effect on nearby bodies. Its

like looking out of a window and seeing all the tree-tops bent in one direction, and inferring that a

strong wind must be blowing in that direction. When particles from nearby bodies are pulled towards a

black hole, the friction results in emit of x-rays. An accretion disk is formed which is detected using x-ray

detectors on earth.

Figure 1 - Gas Jet coming striking off an accretion disk.

A phenomenon known as gravitational lensing can also tell us about the black holes presence. If a

distant galaxy and a black hole are lined up, we see a distorted image of the distant galaxy as if

something in the space were bending the rays coming from the galaxy, like a lens. Einsteins General

Theory of Relativity suggests that a massive object can wrap the space-time fabric so as to bend the light

rays passing through it. So, we conclude that, something massive, which we cannot detect using any of

our conventional means, must be out there in the darkness of the space.

Black holes appear to exist in two radically different size scales. Stellar-mass-black-holes are generally

10-24 times the mass of the sun and are peppered throughout the universe, while supermassive-black-

holes are millions, or even billions, of times as massive as the sun, and lie at the center of virtually all

galaxies including our Milky Way.

How come these destructive giants are wandering in our universe? When massive stars die, they leave

behind a dense remnant core. If the remnant core is about 10 solar mass, the core collapses under its

own gravity to a single point: singularity the innermost part of a black hole. (The outermost part is

called the event horizon.) This dense core has a gravity high enough to not even let light escape its

bound. Thus, a black hole is formed.

One thing to be clear about is that black holes have no more vacuuming power than a normal star of the

same mass. For instance, if the sun were to instantly convert into a black hole, the earth would go cold,

but wouldnt budge from its orbit.

Black holes dont only affect space, but time too. Black holes, with their incredible gravitational pull, are

basically time machines. Get on a rocket, travel to Sgr A* (See Figure 2), ease extremely close to the

event horizon, but dont cross it. For every minute you spend there, a thousand years will pass on Earth.

Its hard to believe, but thats what happens. Gravity trumps time.

Figure 2 - Sgr A* black hole

In a sense, our universe is a black hole too. Think about a two dimensional world a world on a surface

of a sphere. The light beam in that universe would never know the up-direction. The light beam would

never leave the surface of the sphere, essentially being trapped in that dimension. This property not

allowing light escape its bound is of a black hole.

The final point in a black hole singularity is also proposed to be the seed to a new universe. Our

universe is believed to be formed by a violent explosion of an infinitely small point the phenomenon

known as Big Bang. It is proposed that multiple such universes may exist, and singularities can be what

explodes to form all the matter in that new universe.

General relativity theory predicts, that nothing would happen when you reach the event horizon. You

just pass through, unaware that youre now lost to the rest of the universe. Youre fine. Your watch on

your wrist ticks along as usual. Though you would be frozen at the horizon for the observers outside the

black hole. Its often said that black holes are infinitely deep, but this is not true. There is a bottom. You

wont live to see it. Gravity, as you fall, will grow stronger. The pull on your feet, if youre falling feet

first, will be so much greater than the tug on your head that youll be stretched until youre ripped apart

you will be spaghettified.

Besides what we said about the ferocity of black holes, there is still a chance that they could be ruthless.

Samir Mathur, professor of physics at The Ohio State University and black hole sympathizer, thinks that

black holes aren't the ruthless, all-consuming mega-behemoths that we've made them out to be. He

proposed the fuzz ball theory for black holes, which is based on the string theory and suggests that the

event horizon is not rigidly defined, but is fuzzy, and when you reach the horizon, nothing would happen

to you, rather a hologram replica of you would be created and would be sent inside the black hole.

So, we may say that black holes are the terrifying all-swallowing entities wandering in our universe,

which may be the mother of other multiple universes.