I just had an idea not sure if this would work but if we dropped something into very deep water like the marina trench could the pressure crush it small enough to create a black hole?
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$\begingroup$ Welcome to the astronomy SE btw. Earn another badge by taking the tour! astronomy.stackexchange.com/tour $\endgroup$– El BromistaCommented Sep 21, 2016 at 20:21
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1$\begingroup$ Why stop at bottom of marina trench, why not all the way to the center of the Earth. $\endgroup$– Knu8Commented Sep 22, 2016 at 10:01
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$\begingroup$ There is already stuff down there like water and likely dead flora and fauna. Those aren't being crushed into black holes are they? $\endgroup$– zephyrCommented Sep 22, 2016 at 15:28
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3 Answers
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There already is something at the bottom of Mariana Trench. Rocks and stuff. Luckily they haven't been turned into black holes. So empirically, we can say that the answer is no. If it had, it would have attracted its surroundings, and eventually the rest of Earth would fall into it.
To create a black hole, you need to compress a certain mass to within a certain radius. But solids and liquids are really hard to compress. Although the pressure at the bottom of the Mariana Trench is over 1000 atmospheres, water is compressed only by 5%. And solids like rocks and metals are virtually incompressible$^\dagger$.
Even at the center of the Sun, where the pressure is 250 billion atm, the density is only 150 times that of water (under 1 atm). That is, 1 kg of water placed at the center of the Sun would fill not one liter, but $0.7\,\mathrm{cl}$. But to turn a mass $M$ into a black hole, you'd have to compress it to within it so-called Schwarzschild radius, which is given by $ r_\mathrm{S} = 2GM/c^2, $ where $G$ and $c$ are constants. For $M = 1\,\mathrm{kg}$, this equates to $10^{-25}\,\mathrm{cm}$, much smaller than the radius of an atom.
Such conditions arise only in extreme events, such as the core of a dying star collapsing, and even then only the most massive stars. So unfortunately, you won't be able to create a black hole.
$^\dagger$Solids are not entirely incompressible, since otherwise sounds wouldn't be able to propagate through them.
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No, for a black hole to form the core of a star much larger than our sun must collapse into itself, forming a singularity. This happens after a star has expended it's fuel no longer being able to offset the inward force of gravity. The result is a rapid release of its outer layers in a supernova. The resulting core then collapses into the singularity. The mass is so great that this singularity is an infinite bend in space time.
Of note, if we took your object and were able to squeeze it down so small that it's radius reached the Schwarzschild radius, it could become a black hole. The Mariana Trench could not provide enough pressure to this.
There exists little fish and organisms near the bottom of the Mariana Trench. Dropping something like a penny would just cause it be distorted by the pressure above it.
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1$\begingroup$ While we are mostly used to black holes forming from stars, that's not a criterium for something to be a black hole. The LHC at CERN is potentially creating black holes, and they are definitely not dealing with core collapse stars over there. Anything can become a black hole, if it becomes dense enough! $\endgroup$ Commented Sep 21, 2016 at 21:37
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$\begingroup$ @nataliaeire aye, but I didn't want to confuse this person. I didn't want the follow up of, "Yeah it would crush it so small that a black hole would form." Although, my answer is isn't as complete as pela's. However, I'll try and edit my answer to be more complete. $\endgroup$ Commented Sep 21, 2016 at 21:43
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2$\begingroup$ @nataliaeire: Under the standard model, you'd need 1e17 times the energy of the LHC to create BHs from colliding particles. If string theory is correct, you could perhaps create one, but it would evaporate immediately. Even if Hawking radiation is a lie, it would grow too slowly to engulf Earth in billions of years (if there is ≥7 dimensions) or have observable effects in the Universe (if there are 5-6 dimensions). This is not my field of expertise, though, but Earth is hit ~1e5 times per second by cosmic particles with energies ≥ the LCH energy and we're still here, so I think it doesn't work $\endgroup$– pelaCommented Sep 22, 2016 at 10:44
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$\begingroup$ @pela Yes, though, I don't see why you would bring up engulfing the Earth, seeing how that, too, is not a criterium for being a black hole. And that is my point; that to get a black hole you "simply" need to compress something within a certain radius for any given mass. In other words, I thought your answer was more complete. $\endgroup$ Commented Sep 22, 2016 at 21:51
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2$\begingroup$ @nataliaeire: I apologize, I put more into your comment than you deserved. It's just that a couple of years ago, there was quite a lot of criticism from some people who thought that the LHC were able to create BHs, that would then engulf Earth. Your point is absolutely valid. $\endgroup$– pelaCommented Sep 23, 2016 at 9:21
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Theoretically any object with a mass great enough that its own gravity is able to overcome its molecular movement and provided there is no forces to counteract that force such as atomic fission or fusion can in deed implode to a singularity, however the pressures from the sea are far to weak even at the center of the earth to initiate such a reaction it takes a mass of over 3 times that of our sun to even come close. On the other hand it may be possible hypothetically to compress an Eisenstein Condensate kept at temperatures near 0K (say 1k) at extreme pressure might be able to form a mini hole. But the heat caused by that pressure would disrupt the process and even if successful it would evaporate in pico seconds
