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ExtonGuy t1_j584frx wrote

Actually, the speed of light is 299 792.459 km/s. But that's a nit.

Your mass with an escape velocity just a hair under the speed of light would already be practically invisible. Any light that left would be red-shifted to extremely large wavelengths, such as (for example) 300 000 kilometers. That's more than 23 times the diameter of the Earth. Also, the energy of the photons would be corresponding low. Detecting (seeing) such a photon would require an antenna of about that size.

Your mass would be, I guess, some type of hyper-neutron star with a mass of 3.56 x 10^(57) hydrogen atoms. I speculate that quantum fluctuations alone would be enough to cause collapse into a black hole.

The mass doesn't "suddenly" become invisible. It becomes invisible very gradually.

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bgplsa t1_j58ib7a wrote

Great answer but I don’t understand the becoming invisible very gradually part can you elaborate?

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citybadger t1_j59r94t wrote

Light climbing out a gravity well loses energy. Unlike a object with mass, it doesn’t slow down as it loses energy, because it’s light - it can’t slow down. So it instead gets lower in frequency - “red-shifted”. Gamma rays become X-rays, which become ultraviolet light, which become blue visible light, which become red visible light, then infrared, microwave, and radio. Visible light climbing out of ordinary neutron star will be red shifted. Some of the red light will be invisible because it shifted into infrared.

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Sykowsh t1_j5a1wnx wrote

Also relativity. Your atom with speed of just a tiny bit lower than speed of light would have such a relative mass on itself, that it could under the influence of your BH create some sort of space censure around itself,
from the perspective of an outside observer. ....or I confuse apples with pears.

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its-octopeople t1_j584l19 wrote

Gravitational redshift would likely mean that any light escaping from your one-atom-short-of-a-black-hole would no longer be in visible wavelengths. So it might not look visibly different at all.

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neovb t1_j582aiu wrote

Relativity aside, something going the speed your mention would only hypothetically be able to escape the black hole before the event horizon. After it crosses the event horizon it could no longer escape the black hole's gravity.

But I think the answer to your question is no, since the faster something goes the higher it's mass. To reach the speed of light for anything with mass is effectively impossible, as at the speed of light any thing (no matter how small) would have an infinite mass and therefore require infinite energy.

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DarkArcher__ t1_j58laqs wrote

When it comes to escape velocity, mass isn't the only factor. 11.2 Km/s is Earth's escape velocity at the surface. Its lower the higher you go. This also applies to any object wanting to become a black hole, because if you have something that's a hair away from having the right density to become a black hole (the volume in this case being of the space within the event horizon), its just gonna ever so slightly collapse on itself under its own gravity and become a true black hole.

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Anonymous-USA t1_j581h0f wrote

But this hypothetical “mass” would be traveling faster than the speed of light, which no mass can theoretically do.

Even a massless photon cannot escape a black hole, not because of the gravity (the photon has no mass and therefore immune to gravity), but because space through which the photon travels is itself warped. So the “escape velocity” exceeds any information, mass or massless, matter or energy, past the event horizon.

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Unlikely_Concept5107 t1_j59tlj0 wrote

Im no expert but isn’t “gravity” and “warped spacetime” really just the same thing?

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Anonymous-USA t1_j5af6kl wrote

Hard to say since no one actually knows what gravity is! 😆 But the distinction I was making is that a photon has no mass, so light doesn’t actually change directions due to gravity so much as it travels a strait line through a warped space-time.

ie. Gravitational force F=(G × M1 × M2) / D^2

Photon M2 has mass of 0. This suggests it could escape the black hole as there’s no gravitational force between them, but obviously it cannot due to the curvature of space.

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boundegar t1_j59n2ra wrote

Question doesn't really make sense. Verb has no subject. Who or what is "going to the very limit?"

What you might be asking is if a neutron star gradually accretes mass, will it reach a threshold and collapse into a singularity, and the answer is yes, in theory. A bunch of gravitational waves would result, and I think scientists have detected waves with the right pattern - but there's no way to directly observe this.

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egregiouscodswallop t1_j5a6jmt wrote

Since the explosive forces, swirling gasses, and gravitational rotations create a total force that is NOT spherical, there is likely a window of time when part of your blackhole requires an FTL escape velocity while the other hemisphere still lets loose photons and gamma rays. So a critical atom (singular)? No, probably not. There is also an accretion disc around blackholes which block and reflect light back into the central mass. So for a non-zero amount of time, the blackhole is not trapping photons but the blackhole system (the Greater Metropolitan Blackhole) does effectively trap everything.

Tl;dr there would be a window of time and mass during which your escape velocity is sub c but nothing escapes AND/OR your escape velocity reaches c but not uniformly in a sphere.

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softpointjp t1_j58frcr wrote

Escape velocity is not dependent on mass. Like the experiment where a golf ball falls at the same acceleration as a bowling ball. It’s a characteristic of earth or other planet/black hole.

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