If there was a black hole on earth, what would it look like?

Question

If an answer does exist, I'd love to hear it. I'm trying to incorporate a doomed earth story in something I'm writing, and the end of the world I'm going for is a black hole.

Let's say the black hole was created in the Philippines (I chose it because it's on the equator). Here's a map for reference.

If I was standing 90 degrees of that, in Kenya, or if I was standing 180 degrees of that, in Mexico; what would I see in those two separate instances? What if I was standing in Japan above it, or in Australia below it?

Let's also say I was riding a boat towards the source of the black hole. Unlike most imagined scenarios where I am orbiting the black hole and slowly falling into it, this time I'm no longer orbiting it - I'm getting sucked into it instead. I'm imagining that the black hole will "half" be inside Earth and "half" will be in the atmosphere. But as it pulls me in, what will it look like to me (if I was massless, so no tidal forces)? It's probably not going to be a black hemisphere sticking out of the ground. Light will be lensed around it in some way so as to appear like a hole in the air.

Also, if the black hole was very small, it probably won't have a strong gravitational pull, and assuming it doesn't disappear, you'd be able to look at it (or at least, its effect on the light in its surroundings). Of course, as you approach it, it would still have an event horizon, so spacetime would still be warped if you're near enough and the surroundings will still experience tidal forces.

As the black hole gains mass, it will get larger, and so its event horizon will increase. If I was standing in Kenya and the event horizon "washes over me," (as in a water wave) what will I see?

I've so far imagined that, at least when seen from outer space, there will be a hole on the ground and light will be lensed around it. When you are on the ground, though, it becomes a bit harder to imagine.

I do hope someone can lend me a hand!

Edit: Someone had previously answered this question, but I'm not sure why it's been deleted. It was pointed out to me, though, that a black hole cannot stay in place. So an additional question for me is, does that mean it is impossible to be standing still, and the event horizon "washes over you"?

Edit2: Here's a guiding thought experiment that could answer the question. Imagine that you are in outer space directly above the black hole, looking at the black hole that is on the earth's surface. Can you imagine what it would look like? It would simply be a hole with the surrounding light gravitationally lensed around it (possibly lensing the entire earth if it's big enough - but let's say it's not).

Now imagine that you are on the direct opposite of where you were above - you're right behind the black hole this time, looking directly at the black hole but unable to see it because the earth is blocking your view.

Now try to imagine, from the second image, rotate the earth into the first image. I find it a bit hard to do. Just as the black hole is appearing as you rotate the earth, how would the light be lensed?

Answer 1

An interesting and horrifying possibility for your book could be that of a tiny black hole with negligible mass relative to the mass of the Earth. It would silently sink into the ground, completely unnoticed. It would make damped oscillations around the center of the Earth until eventually staying within the nucleus. There it would stay unnoticed, slowly growing like a parasite. The Earth radius would start to diminish, and thus the crust would have to adapt by means of earthquakes - very weak at first, but of increasing frequency and strength. Eventually, chains of volcanoes would appear along giant fault lines, heating and poisoning the atmosphere, bringing total obliteration. After that, the Earth would continue shrinking until all that was left would be a tiny black hole with little more than one Earth mass in the place where our planet was. And the Moon would stay there as a horrified witness of the catastrophe.

Nothing on Earth would be able to stop the process and save us. Nothing except Chuck Norris.

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Note: Classical GR black holes are fully determined with just three values: mass, electric charge and angular momentum (No-hair theorem). If the charge is large enough in the black hole of your novel, then the hero might be able to confine it by using strong magnetic fields.

Answer 2

There are some visualizations of what it would look like to travel past the event horizon, assuming you survive the process of course.

This video gives you an idea of what the black hole looks like. What you see is a distortion of everything around you, as bit like looking through curved glass.

Unfortunately these videos aren't set on Earth; I'm sure the hole chewing up Earth would look spectacular, but I don't know how long this might last. I suspect things would get pretty hot as matter is compressed on its way towards the hole.

Answer 3

The premise of the question is wrong: if you dropped a small black hole (one less than the mass of the Earth) into the Earth, only a small fraction of Earth's mass would end up in the black hole.

The maximum angular momentum of a black hole of mass $M$ is $\frac{G M^2}{c}$. For the Earth's mass, this is around $7.9 \times 10^{30}$ kg m$^2$/s.

The angular momentum of the earth is around $7.1 \times 10^{33}$ kg m$^2$/s.

That angular momentum has to go somewhere, and the only place it could go is into pieces of the Earth that either end up orbiting the black hole or escaping to infinity. These pieces would presumably comprise nearly all of the mass of the Earth.

I don't know exactly what would happen. Probably, the Earth would eventually be destroyed, but I really don't know how fast or how it would happen. Whatever happens, you are probably going to get killed in some way other than being sucked into the black hole.

Answer 4

In this, I have taken the assumption that the singularity is created within the atmosphere, perhaps by an experiment or some such, rather than a wandering black hole, and therefore starts life with much less mass than the earth. A naturally created black hole travelling in space would generally be far more massive, having been created from a collapsing star. in the latter case, the planet would simply be shredded as it nears the event horizon, killing everyone on the planet, or possibly just swallowing the earth in seconds, dependent on the relative motions and trajectories of the two

The thing about a singularity is that any matter which falls within its event horizon is consumed, and from an external frame of reference instantly becomes part of the mass of the singularity. Any mass which exists within the atmosphere of earth will move towards the earth at an acceleration of 10 m/s/s. A singularity would not be slowed by air resistance, as it would draw in any air molecules that contacted the event horizon, rather than displace them.

Also, due to the curvature of the Earth, nothing within the atmosphere near the philipines would ever be visible from 90 or 180 degrees away in any direction.

Therefore this singularity would fall rapidly to earth, where it would proceed through the crust experiencing drag equivalent to the ability of whatever matter it contacts to resist, albeit briefly, being torn apart by the singularity pulling in any matter contacting the event hozizon. once through the crust to the liquid part of the core, it would accelerate again, initially passing directly through the gravitational centre of the earth repeatedly back and forth, until it consumes enough matter to shift the centre of gravity of the earth, at which point, the singularity and the earth would begin to orbit their common centre of gravity. This would result in erratic changes as the singularity consumes matter in intermittent pulses, as it passes in and out of voids created by it previous motions.

as the singularity consumes more and more of the planet, the earth would break up under the vibrations caused by the wobbling motion within, speeding the growth of the singularity, as the remains of the crust fall inwards to the common centre of gravity, where they will be consumed by the ever growing black hole. when the earth is fully consumed, the black hole would continue to orbit the sun in its place, until it consumes enough orbiting debris to begin a spiral orbit towards the sun, likely collecting venus and mercury on the way. when it eventually hits the sun, it will repeat the process on a much larger scale, either consuming the star entirely, leaving a black hole in its place, or potentially destabilising the sun enough that it goes supernova before the black hole can consume it.

If the singularity had enough mass to survive longer than a few seconds after creation, without evaporating, I would expect it to destroy the earth completely in just a few hours, with all life being wiped out quite early on due to the cataclysmic disruption to the crust.

If a living person were to enter the event horizon, they would die, torn apart by the forces inside. However, they would feel nothing as the electrical nerve impulses from the affected nerves would never reach the brain, themselves being pulled into the centre of the singularity.