Falling into a Black Hole

Parts of a black hole and the fate of an object that falls into one

Hello fellow enthusiasts, it is great to see you again.

As is obvious from the title, this article is in continuation to my previous article on the Black Holes. Today, we would be talking about the parts of a black hole and the fate of objects that fall into it. I hope you are as excited as I am. So, let’s begin.

A beautiful depiction of a black hole, because, why not?

We will begin with some basics, starting with the knowledge of what the various parts of a black hole are.

1.      Singularity: Singularity is the point in space where the mass of a black hole is supposed to be concentrated. The point has zero volume and an infinite density. It is the hole part of the black hole. (The very existence of a singularity in a physical world is mindblowing. It makes for an interesting point of discussion.)

2.      Event Horizon: The event horizon is a sphere of zero thickness around the singularity. It is marked by the surface at which the gravitational pull of a black hole is so strong that even light cannot escape. For escaping the event horizon your velocity should be greater than the speed of light. And which according to the General Theory of Relativity is impossible. So, no escape! It makes up the black part.

3.      Photon Sphere: The Photon sphere is the region around a black hole with gravity so strong the photons start to revolve around it. It is a point where light doesn’t necessarily get sucked inside the black hole, but doesn’t necessarily return. Its thickness equals one-half times that of the Schwarzschild radius (or the radius of the event horizon).

4.   Ergosphere: The region around a black hole where it is not possible to remain stationary is called an ergosphere. It exists only in rotating black holes. Its shape is that of an oblate spheroid - bulged at the equator and flattened at poles. Since the Ergosphere is outside the Event Horizon, it’s possible to escape the black hole from here. When the object leaves, it leaves with extra energy accumulated from the spinning black hole.

Accretion Disk: Material, such as gas, dust, and other stellar debris that has come close to a black hole but not quite fallen into it, forms a flattened band of spinning matter around the event horizon called the accretion disk. An accretion disk is most clearly visible in a quasar. It may or may not be present in all the black holes. 

Parts of a black hole

So, it was as far as parts of a black hole goes. Now, let’s jump to the fun part!

What would happen if we fall into a black hole?

As we will study later but we now take it for its word, gravitational fields bend space-time. A star situated behind our sun would appear a bit displaced due to this warping of space. But what happens when a massive object as massive as an entire galaxy or a black hole comes in between? We would see a distorted, smudged, or smeared image. If we are looking at a galaxy, say A, and galaxy B is in between, galaxy A would look to us like a ring or smudge around galaxy B. This phenomenon is known as gravitational lensing.

Gravitational Lensing by a black hole

This is one phenomenon we needed to know before we could proceed. Let's get going!

For simplicity, we will take an uncharged, non-rotating black hole that is not already feeding. As we approach this black hole, distortion of the sky grows greater and greater (due to gravitational lensing). A large part of our field of view looking forward into the black hole is filled with darkness. When half of our field of view is filled with darkness, we have reached the photon sphere (where the photons orbit the black hole here, remember?). If we could theoretically stop for a moment and look sideways, we would see the back of our own heads. As the light has travelled from our back and after revolving around the black hole came to us again.

Photon Sphere

The gravitational field also warps time. For an observer looking at us, time would appear moving slow. This is the phenomenon of time dilation. For them, our approach to the black hole would seem to get slower and slower, until we reach a point – The Event Horizon. Space and time are so warped up here we have only one direction of motion, and that is inside it. We can only move in the forward direction. And as for the observer, we would appear frozen in space. 

The light coming from our body would get increasingly red-shifted until we disappear (The wavelength would keep on increasing even if it is not in the visible region. Our information or the information of any object that has fallen into the black hole would be preserved on its surface. Thus, information is conserved. This statement has more meaning than it appears now. Its significance will be better visible when I would talk about Hawking Radiation). They would not see us actually get past the event horizon.

Astronaut frozen in space

But for us, things would be completely different. We would continue our journey inside the event horizon, to our inevitable death!

Our view of the whole universe would get compressed into a smaller and smaller point behind us. We may die before we actually reach the event horizon by hitting a firewall (A black hole firewall is a hypothetical phenomenon where an observer falling into it encounters high-energy quanta (plural for quantum; which is the minimum amount of any physical entity involved in an interaction) at or near the event horizon). If we enter a black hole, large enough, we can remain for hours going inside it before it starts hurting. And why would it hurt? The answer is, as we approach singularity, the gravitational field gets so strong that even a small distance of say 1 cm would have a difference of millions of times of gravitational pull. The molecules in our body will be torn apart and we would get stretched to billions of pieces. In fact, this phenomenon has a special name! Spaghettification. 

You die either way

Here, we will die! Actually, we would not be alive to see what happens to us as we reach the singularity. We would never be alive to see a naked singularity. The singularity always exists in the future for us. This way in which the Universe protects or “censors” a black hole from being observed gives rise to a hypothesis – The Cosmic Censorship Hypothesis. The naked singularity and cosmic censorship hypothesis make for our next topic of discussion.

But, the question remains, what happens when our remains finally reach singularity?

We actually don’t know. We may get sucked into the singularity and completely disappear against all the laws of physics.

or

As another theory suggests, we may enter a wormhole. These are shortcuts in space-time. Inside a wormhole, we can travel faster than the speed of light from one point in the Universe to the other. It makes use of theories involving other dimensions. It is something like “Doraemon’s anywhere door”. This also a potential candidate for an interesting discussion. But, of course, you know we can’t cover it here. (As we would get completely off-topic plus the word limit…) So, let's be hopeful future articles bring more about them.

I hope you enjoyed reading this article as much as I enjoyed writing it. I'll sign off now, but before that,

We are doomed.

here, I present to you our doom. :)

See you later!