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Size of black holes limited

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Clawg
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Good news if you plan to live forever:

A new study by researchers from the US and Chile suggest there is an upper limit on the mass of black holes. Using a variety of observational data they trace the accretion history of black holes, from which the mass and growth rate of the black holes can be determined. A study of the predicted distribution of black holes with varying masses according to the accretion history and its comparison to observed distribution, suggests the mass of black holes is upper bound.

http://thefutureofthings.com/news/1313/is-...es-limited.html

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My guess is that the limit is asymptotic, that "gravity can't get to the other side in time" or something like that. Or it could be that such black holes evaporate using TWO different kinds of methods, one being hawking radiation and another being a low density evaporation similar to stuff on the inside phasing out. Or maybe, stuff is being pushed through the singularity into a new universe. Who knows?

Edited by TuringAI
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Well, if there is anyway to go out, I'd at least like to have the experience of being sucked into a black hole. Maybe Jesus is on the other end? B)

I don't think you'd like that experience. As you got closer to the black hole, the gravity at your head would be drastically different from the gravity at your feet. The result: you'd rip in half. The same would happen as the two halves of you moved closer to the black hole: your halves would split in half, etc. It'd be like someone just picked you up and tore you into shreds. If someone was in orbit outside the black hole, watching you go in (yes, you can orbit a black hole just as you can orbit a star), they'd see your bits rip to shreds, and then at the last second, as you crossed the event horizon, the image of your remains would become frozen, and then fade to red, then disappear into the infrared, to the micro-wavelength, to the radio wavelength, etc. As for you, if your head remains intact across the event horizon, and you somehow remain conscious, right before you're crushed at the center, in that fraction of a fraction of a second, you could look out at the universe and see the entire future of the universe pass by in an instant.

(at least, that's the popular interpretation)

Edited by brian0918
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I don't think you'd like that experience. As you got closer to the black hole, the gravity at your head would be drastically different from the gravity at your feet. The result: you'd rip in half. The same would happen as the two halves of you moved closer to the black hole: your halves would split in half, etc. It'd be like someone just picked you up and tore you into shreds. If someone was in orbit outside the black hole, watching you go in (yes, you can orbit a black hole just as you can orbit a star), they'd see your bits rip to shreds, and then at the last second, as you crossed the event horizon, the image of your remains would become frozen, and then fade to red, then disappear into the infrared, to the micro-wavelength, to the radio wavelength, etc. As for you, if your head remains intact across the event horizon, and you somehow remain conscious, right before you're crushed at the center, in that fraction of a fraction of a second, you could look out at the universe and see the entire future of the universe pass by in an instant.

(at least, that's the popular interpretation)

Actually, if the black hole were large enough, spaghettification wouldn't occur until well after you have passed the event horizon. Passing the event horizon would not seem to be anything special.

Outside the event horizon, a black hole has a "photon sphere" where light orbits the black hole. If you were in the photon sphere, with the black hole below, and you looked directly ahead, your line of sight would go clear around the black hole, and you'd see the back of your own space helmet. As far as I can tell, you would be surrounded by an inside-out funhouse-mirror image of yourself. Below, you would see only blackness. (If the black hole is very large, you might still not be able to see yourself. Your image would be a thousand miles away and only as tall as you. It would be a very thin line at the horizon.)

Once you are inside the photon sphere, you'd have to look up at a higher and higher angle just to see outside of the black hole. So imagine being surrounded by a funhouse image of yourself, suspended over blackness, and seeing a circle above you with the entire universe inside.

It would be very bright close to the "horizon" because at that angle your line of sight spirals around the black hole many times on its way out. All the light from around the black hole would be gathered into a small region of arc. If you looked straight up you would see straight out. It would be darker. The image of the universe would repeat inside the circle, with more and brighter repetitions closer to the edge.

As you fell into the hole, the funhouse image of yourself would get closer, and closer. The horizon would get higher up, smaller, and brighter. Maybe the curvature of space would reach a point where you could touch your funhouse image self and feel yourself touching yourself. You are effectively reaching around the black hole! But this image of you would keep getting closer. Eventually the "image" would crush you; you'd be crushed against yourself. That of course assumes you're going in alone.

This crushing power would encourage things to stretch out vertically. Your subatomic particles would probably slide above or below each other, but eventually each one would each be crushed against an image of itself.

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Outside the event horizon, a black hole has a "photon sphere" where light orbits the black hole. If you were in the photon sphere, with the black hole below, and you looked directly ahead, your line of sight would go clear around the black hole, and you'd see the back of your own space helmet. As far as I can tell, you would be surrounded by an inside-out funhouse-mirror image of yourself. Below, you would see only blackness. (If the black hole is very large, you might still not be able to see yourself. Your image would be a thousand miles away and only as tall as you. It would be a very thin line at the horizon.)

Actually, you'd see yourself whatever direction you looked. At a given point near a mass, the same velocity gives an orbit with the same semi-major axis, no matter what the direction--horizontally, at a slope, vertically.... So if light speed is circular orbital velocity at your altitude above the singularity, it won't matter what direction you look. (Straight up or down *might* be an exception).

Actually you don't even have to be at that exact altitude; any altitude for which light's velocity is less than escape could lead to this phenomenon (it's just that light will unavoidably have an elliptical (non-circular) orbit at that altitude.

Caveat to all of this: I am thinking in terms of Newtonian orbital mechanics; general relativity might give different results.

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Actually, if the black hole were large enough, spaghettification wouldn't occur until well after you have passed the event horizon. Passing the event horizon would not seem to be anything special.

Outside the event horizon, a black hole has a "photon sphere" where light orbits the black hole. If you were in the photon sphere, with the black hole below, and you looked directly ahead, your line of sight would go clear around the black hole, and you'd see the back of your own space helmet. As far as I can tell, you would be surrounded by an inside-out funhouse-mirror image of yourself. Below, you would see only blackness. (If the black hole is very large, you might still not be able to see yourself. Your image would be a thousand miles away and only as tall as you. It would be a very thin line at the horizon.)

Once you are inside the photon sphere, you'd have to look up at a higher and higher angle just to see outside of the black hole. So imagine being surrounded by a funhouse image of yourself, suspended over blackness, and seeing a circle above you with the entire universe inside.

It would be very bright close to the "horizon" because at that angle your line of sight spirals around the black hole many times on its way out. All the light from around the black hole would be gathered into a small region of arc. If you looked straight up you would see straight out. It would be darker. The image of the universe would repeat inside the circle, with more and brighter repetitions closer to the edge.

As you fell into the hole, the funhouse image of yourself would get closer, and closer. The horizon would get higher up, smaller, and brighter. Maybe the curvature of space would reach a point where you could touch your funhouse image self and feel yourself touching yourself. You are effectively reaching around the black hole! But this image of you would keep getting closer. Eventually the "image" would crush you; you'd be crushed against yourself. That of course assumes you're going in alone.

This crushing power would encourage things to stretch out vertically. Your subatomic particles would probably slide above or below each other, but eventually each one would each be crushed against an image of itself.

Yeah, that sounds cool. 2 tickets please.

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  • 2 months later...

A thousand miles across? That sounds kind of teeny tiny.

Looks like people have lots of ideas of what constitutes a black hole. It sure sounds to me like there'd be plenty of room in the great Outer Space for lots and lots of "big bangs" capable of sucking in, then giving birth to, new galactic clusters every other fortnight, at least.

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So if there's an upper limit, then given enough "food" for a black hole to feed it well beyond the upper limit, and at a faster rate than its evaporation rate, what would happen? Would it explode?

It wouldn't "explode". Decay is more like it. The only 'explosion' that would happen is at the quantum black hole limit level.

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  • 6 months later...

Several of you have referred to the evaporation of black-holes. The rate of evaporation is inversely proportional to the square of the mass. So except for microscopic black-holes, evaporation is negligible. See http://en.wikipedia.org/wiki/Hawking_radiation for more details.

I have been away so long, I have forgotten how to spell-check on this forum.

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