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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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