Why Is A Black Hole Really So Special?

The first direct image of a supermassive black hole at the core of Messier 87 galaxy (image credit: EHT Collaboration)

The notion of a black hole has always stimulated my curiosity. There is just something about this unfathomable entity that pulls me towards it (pun intended). Be it from a scientific perspective or a science fiction perspective, black holes are full of mystery and awe.

After diving headlong into the topic, I have decided to write a series of essays that cover the various aspects of black holes — from the seemingly trivial to the most profound. This essay is the first in the series, where I try to cover the fundamental intuitions surrounding the notion of black holes.

To this end, I will be explaining the idea behind black holes in two levels of intuition — one targeted at a child, and one targeted at an adult. If you are as excited for this topic as I am, strap yourself in for the ride. Who knows what exists beyond the event horizon?

This essay is supported by Generatebg

The Black Hole — Explanation to a Child

Imagine a child who is roughly ten years old. Such a child would not have learnt about most physics concepts necessary to understand black holes. However, curiosity knows no bounds. Here is my take on explaining the intuition behind a black hole to such a child.

A black hole is a special physical entity that forms when stuff that normally occupies a lot of space gets crushed and forced into a significantly smaller space. Imagine a sponge ball. If you crush this ball, its weight does not change, but the space it occupies (known as volume) gets smaller. This phenomenon is what we call an increase in density.

Imagine the same phenomenon happening to a star. When a star is heavy enough to explode into a supernova, the exploding matter loses the ability to escape the star’s own gravitational pull.

Under certain specific conditions, this turns into a chain reaction where the star’s core collapses into itself. The star’s core is unable to escape the collapse because it does not have enough thermonuclear fuel left to power its way out. To you and me, this event appears as if the star is eating itself up.

Why is the Black Hole Special? — A Child’s Version

A black hole is formed when the density of matter increases beyond a certain threshold. Beyond this threshold, anything that wants to escape the gravitational pull of the black hole needs to travel faster than the speed of light. That’s right. Even light cannot escape a black hole.

Since any light that gets into the black hole cannot escape, we cannot observe what is going on inside it. This is what makes it a mystery. Now you might be wondering why light approaches a black hole in the first place. A black hole doesn’t suck in stuff like a vacuum cleaner.

Physicist Albert Einstein showed that a black hole bends the space around it in such a manner that the entire space in its vicinity is completely bent towards it. Anything that enters this space is bound to head into the black hole, as there is no other path available. To appreciate how celestial objects bend space around them, check out the following experiment demonstrated by a very clever teacher.

In the case of the black hole, the bending is so strong that anything that is close enough has no way to escape. That is what makes black holes both mysterious and special at the same time.

---

The Black Hole — Explanation to an Adult

Imagine an adult who has a basic understanding of physics and has reasonable real-world experience when it comes to physical phenomena. Such a person would not be an expert in either physics or mathematics but would be able to logically reason with the help of the fundamentals that they possess. Here is my take on explaining the intuition behind a black hole to such an adult.

In a way, black holes represent the limits of our current understanding of physics. While Newtonian laws treat gravity as a force, Einstein’s theory of relativity treats gravity as a geometric property of space and time. To get a vague understanding of how this works, the video that I have linked above is very resourceful.

A black hole is a geometric feature in the fabric of spacetime where gravity acts like a sink. Anything that passes close enough to a black hole gets pulled into this gravitational sink. Let’s get a little more precise with this ‘close enough’. The boundary beyond which no object can escape a black hole’s gravity is known as the event horizon. As I mentioned previously, not even electromagnetic radiation such as light can get past the event horizon.

Having said this, black holes are not evil beings that go on sucking in everything in their path. Say there existed a black hole in the place of the sun in our solar system. Further, suppose that this black hole possessed the same mass as our sun.

In such a case, the Earth would orbit around this black hole just like the sun, and wouldn’t get pulled into it. On the ‘known’ side of the event horizon, black holes are mostly just like any other celestial body when it comes to physics as we understand it. It is beyond the event horizon towards the centre of the black hole that we don’t understand well yet.

Why is the Black Hole Special? — An Adult’s Version

In 1915, Albert Einstein developed his Theory of General Relativity, which allowed for the existence of black holes (no one had observed black holes at that point). This ‘possibility’ did come, however, with a catch: a singularity. Let us say that there are two indestructible objects just outside the event horizon of a black hole. One of them decides to jump into the black hole (the seeker) and the other one decides to observe (the observer).

As the seeker goes into the black hole towards its centre, the observer experiences the seeker moving towards a point in space before leaving a visual record on the event horizon (the observer cannot experience what happens beyond this point). As the seeker moves beyond the sight of the observer, the seeker experiences themselves moving towards a point in time (not space!) — something inevitable!

In science, singularities should be taken with a grain of salt. Usually, they indicate the limits of a theory and not the limits of science itself. Therefore, it is prudent to assume that we need a better understanding of physics to explain what happens beyond the event horizon.

In a way, newer developments in physics such as the Quantum Field Theory in Curved Spacetime aim to tackle these challenges.

These mysteries are what make the black hole such a special phenomenon to study and explore.

Final Remarks

What I have tried to present in this essay is just a rough intuition for the notion of a black hole. There are so many more interesting details surrounding just about every aspect of black holes that make the whole topic even more fascinating.

As I mentioned before, I will be writing a series of essays on this topic. Throughout the series, I will be covering each significant detail one at a time. If you feel that there are specific details that you wish for me to cover, please do let me know in the comments section!

---

Reference and Credit: Janna Levin.

If you’d like to get notified when interesting content gets published here, consider subscribing.

Further reading that might interest you:  How Can You Hear Acceleration Without Modern Technology? and How To Tell A Real Law From A Fake One?