Sahaana V
- Apr 27, 2021
- 5 min read

Dose of STEM: A Non-Terrifying Guide to Vacationing Near a Black Hole

Are you intrigued by the idea of embarking on a vacation to a black hole? Is it even conceivable? Black holes are one of the most violent celestial objects in the universe. You may have heard the cautionary tales of being stretched and contorted to the point of disintegration if you venture too close to a black hole, ultimately succumbing to its voracious appetite while your energy remains eternally trapped. With such perilous risks, why should we entertain the notion of vacationing near something so dangerous? Let us dive in to understand black holes better. Let's delve deeper into the captivating realm of black holes to gain a better understanding.

PART 1: VACATIONING NEAR A BLACK HOLE

WHAT KIND OF BLACK HOLES CAN WE VISIT? WHAT SITES OF ATTRACTION ARE THERE? WHERE CAN I STAY?

THE ANSWER: You can visit supermassive spinning black holes (You read that right)

Short explanation:

The reason why you should visit a spinning black hole is that it is possible to narrowly escape the event horizon (if, of course, you are from the future or belong to an advanced civilisation). Why a big black hole? A smaller black hole is more dangerous because they cause more tidal effects, resulting in spaghettification before you reach the event horizon. The black hole is the site of attraction (pun intended), but it is better to view it from a safe distance, which could be more than 1AU (96 million miles). Beware of radiation from the accretion disk!

Long explanation:

When a massive star nears its end, it collapses under its own gravity to form a tiny black hole. But eventually, this black hole gets bigger due to its insatiable hunger. This star, which eventually becomes a black hole, spins and according to Newton's law, an object that is spinning will not stop unless something is stopping it. It has angular momentum, and to conserve this angular momentum, as the star keeps on shrinking, the momentum will make it spin faster and faster till it collapses to form a black hole. The black hole continues to spin with that speed.

Every black hole has an event horizon, the point beyond which nothing can escape, and a singularity, where all the mass which was sucked in is concentrated. To be specific, a singularity is a point in space with no surface area. In a spinning black hole or a Kerr black hole (there are two types of black holes based on spin — Schwarzschild and Kerr black hole), it is called a ringularity, with zero thickness, no surface, and a very fast spinning speed! (Remember the conservation of angular momentum?) When a black hole spins at such a high speed, it drags space along with it; it warps space and time. As a result, a region of space-time called the ergosphere develops around the black hole.

An ergosphere is a crazy place! Since the Black Hole transfers its kinetic energy to everything in the ergosphere, you would be continuously spiralling around till you enter the event horizon. Then, well, you’re dead meat; to be specific, you would undergo spaghettification; you would be vertically stretched and horizontally compressed until you break and be lost forever. To stay still in an ergosphere, you need to travel faster than the speed of light. It is impossible! But here is a trick - we can use the energy in the ergosphere, and it is abundant!

We can use the Penrose process, named after Sir Roger Penrose, the 2020 Nobel laureate in Physics. He realised that energy transfer can occur in the ergosphere itself and designed this concept in 1969. Imagine that you are stuck in a whirlpool. If you want to achieve a high speed to get out, you would swim in the direction of the whirlpool. Similarly, in a black hole’s ergosphere, you may want to do that but also leave something behind.

If we launch a rocket into the ergosphere, it can be split into 2 parts where one part would fall into the black hole, and the other would be ejected out at immense speed! Does that sound familiar? You may have seen the movie Interstellar which illustrates the same concept. However, if you are a normal human being, it is easier said than done.

Penrose Process: A part of the rocket falls into the black hole and the other part is ejected.

A FRIEND OF MINE FELL INTO A BLACK HOLE— WHAT DO I DO?

THE ANSWER: We don’t know yet, but most probably you can’t do anything about it.

Short explanation:

Hawking radiation may come to their rescue, at least theoretically. However, chances are, your friend will not come back.

Long explanation:

Professor Stephen Hawking, in 1974, had theoretically found out that black holes emit black-body radiation* because of the spooky quantum effects near a black hole. It is created by the conversion of quantum energy fluctuations into particles-antiparticle pairs near the event horizon. One falls into the black hole and the other escapes before they annihilate each other. The particle that escapes has positive energy, whereas the particle that falls into the black hole has negative energy relative to the outside universe. Hence, the black hole loses energy and thus mass. As the black hole emits energy, it gets smaller and smaller (it is recommended you travel as far away as you can since it is getting smaller), and eventually, it disappears.

However, it was later found out that Hawking radiation, in essence, carries no information, and this contradicts Quantum mechanics. Professor Hawking's calculations showed that quantum information is destroyed. If you are determined to bring your friend back by finding a better way and proving Hawking and other physicists wrong, you can use this website as a starting point.

WHAT ARE THE WARNING SIGNS THAT I AM TOO CLOSE TO A BLACK HOLE?

THE ANSWER: Radiation, time dilation and spaghettification.

Explanation:

In the accretion disk (a disk of debris outside the event horizon), gravity compresses the debris, which in turn increases the temperature. This causes it to produce tons of lethal radiation. As you get closer to a black hole, time will pass by slower for you as compared to the rest of the universe. Imagine that you are on a spacecraft and are going around a black hole, say, at the speed of light (this is a hypothetical situation; it is impossible to travel at the speed of light). Time would have passed slowly for you. However, the clock on Earth is moving much faster. In fact, many years would have passed on Earth! You would be a few years older, but the people on Earth would be much older than you. This phenomenon is called time dilation. Spaghettification needs no more explanation.

PART 2: BLACK HOLE CIVILISATIONS (COMING SOON)

Abstract

What are black hole civilisations? Is it possible for humans to inhabit a place close to a black hole? (Please note that by close, we mean the shortest, safe distance) Stay tuned for our next article on black hole civilisations.

Do you know any cool facts about black holes? Do you know any other ways to harness energy from a black hole? Comment down below!

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