History UsefulNotes / BlackHoles

7th Jul '17 2:11:23 AM Tightwire
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Black Holes don't actually, technically, emit anything, despite what people say about them emitting radiation[[note]]This may not be true. Due to quantum effects at the horizon, a black hole emits a form of black body radiation and very, VERY slowly loses mass until it eventually evaporates. However, the energy of the radiation 'emitted' by a black hole is inversely proportional to its mass. This means that lighter black holes can quickly evaporate in a burst of radiation; this also means that larger black holes won't be able to evaporate, or even lose mass, for quite some time, due to the cosmic microwave background. This form of radiation is called "Hawking radiation", named after its discoverer (well, "predictor" wold be more accurate, no one has ever actually been able to observe this radiation yet - due to obvious reasons) Stephen Hawking. You can read more about this in [[https://en.wikipedia.org/wiki/Hawking_radiation the other wiki]]. However, until irrefutable evidence is found, it's just a hypothesis despite the fact that it's mathematically all working out.[[/note]]. That's the extreme conditions the matter entering the black hole is subject to. If you heat something up, it will give off radiation. And the matter entering a black hole gets very, VERY hot with all the spinning and stretching and friction and gravity it's going through. Nothing leaves after it's past the Event Horizon itself. However because a black hole is just so awesome, the matter wouldn't achieve those conditions in any other way, so it kind of is, except it's not.

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Black Holes don't actually, technically, emit anything, despite what people say about them emitting radiation[[note]]This may not be true. Due to quantum effects at the horizon, a black hole emits a form of black body radiation and very, VERY slowly loses mass until it eventually evaporates. However, the energy of the radiation 'emitted' by a black hole is inversely proportional to its mass. This means that lighter black holes can quickly evaporate in a burst of radiation; this also means that larger black holes won't be able to evaporate, or even lose mass, for quite some time, due to the cosmic microwave background. This form of radiation is called "Hawking radiation", named after its discoverer (well, "predictor" wold be more accurate, no one has ever actually been able to observe this radiation yet - due to obvious reasons) Stephen Hawking. You can read more about this in [[https://en.wikipedia.org/wiki/Hawking_radiation the other wiki]]. However, until irrefutable evidence is found, it's just a hypothesis despite the fact that it's mathematically all working out.[[/note]]. That's the extreme conditions the matter entering ''entering'' the black hole is subject to. If you heat something up, it will give gives off radiation. And the matter entering a black hole gets very, VERY hot with all the spinning and stretching and friction and gravity it's going through. Nothing leaves after once it's past the Event Horizon itself. However because a black hole is just so awesome, unique in how it operates, the matter wouldn't achieve those conditions in any other way, so it kind of is, except it's not.
7th Jul '17 1:53:07 AM Tightwire
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Black holes are strange things. Besides the singularity at the center[[note]]Assuming it exists, since it's believed it's an artifact caused by breakdown of relativity under those conditions, that would disappear with a -still not existent- theory of quantum gravity[[/note]], there is the event horizon, the point of no return, that once you cross it...[[DepartmentOfRedundancyDepartment you can't return]]. Once inside the event horizon, you literally cannot go back: spacetime is curved in such a way by the black hole's mass that any path you take leads to the same place: the singularity. In three-dimensional space the Black Hole is not a disc. The singularity is an infinitely small point in space that sucks things in from all around, so the event horizon is more like a ball - with the singularity at the center. Rotating black holes also have an ergosphere: a region near the event horizon, where space-time spins around the black hole at speeds so great that you'd need to move faster than light just to stay still, let alone move in a direction counter to the black hole's rotation.

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Black holes are strange things. Besides the singularity at the center[[note]]Assuming it exists, since it's believed it's an artifact caused by breakdown of relativity under those conditions, that would disappear with a -still not existent- theory of quantum gravity[[/note]], there is the event horizon, the point of no return, that once you cross it...[[DepartmentOfRedundancyDepartment you can't return]]. Once inside the event horizon, you literally cannot go back: spacetime is curved in such a way by the black hole's mass that any path you take leads to the same place: the singularity. In three-dimensional space the Black Hole is not a disc. disc, just like the sun is not a big yellow circle. The sun is a sphere, an event horizon is a smaller sphere, and the singularity is an infinitely tiny ball so small point in space and tightly packed that sucks things in from all around, it has basically turned itself ''inside out'' - so when you are inside the event horizon is more like a ball - with singularity, you are inside the singularity at the center.ball. Rotating black holes also have an ergosphere: a region near the event horizon, where space-time spins around the black hole at speeds so great that you'd need to move faster than light just to stay still, let alone move in a direction counter to the black hole's rotation.
4th Jul '17 8:26:39 PM Oh_what_fun
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''And it is getting closer.[[note]]Not exactly accurate. An engine that could achieve FTL by definition can reverse time and throw you into the past, that is, away from the hole. Just point yourself in ANY fucking direction and hit accelerate: once you break the light barrier, time reverses polarity and shoots you from the hole. And a hypothetical engine that achieves FTL without time paradoxes does so by changing the curvature of space around you, again foiling the black hole. On the other hand, it's hard to predict in what exact time period of the universe will you arrive when you break free; most likely, you'll be lost in time. Oh, and, by the way, if you have a magical spaceship that just can accelerate to any velocity, you have an ability to kick physics in the nuts and take names, because screw you, Einstein. So why not just rip through the event horizon with your bare hands and march out, whistling Dixie? (This Troper thinks you're full of shit. Correct me if I'm wrong, but wouldn't FTL travel mean nothing, if not even light can escape? So if it's faster than light, what difference does that make?)[[/note]]''

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''And it is getting closer.[[note]]Not exactly accurate. An engine that could achieve FTL by definition can reverse time and throw you into the past, that is, away from the hole. Just point yourself in ANY fucking direction and hit accelerate: once you break the light barrier, time reverses polarity and shoots you from the hole. And a hypothetical engine that achieves FTL without time paradoxes does so by changing the curvature of space around you, again foiling the black hole. On the other hand, it's hard to predict in what exact time period of the universe will you arrive when you break free; most likely, you'll be lost in time. Oh, and, by the way, if you have a magical spaceship that just can accelerate to any velocity, you have an ability to kick physics in the nuts and take names, because screw you, Einstein. So why not just rip through the event horizon with your bare hands and march out, whistling Dixie? (This Troper thinks you're full of shit. Correct me if I'm wrong, but wouldn't FTL travel mean nothing, if not even light can escape? So if it's faster than light, what difference does that make?)[[/note]]''[[/note]]''
4th Jul '17 8:14:54 PM Oh_what_fun
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''And it is getting closer.[[note]]Not exactly accurate. An engine that could achieve FTL by definition can reverse time and throw you into the past, that is, away from the hole. Just point yourself in ANY fucking direction and hit accelerate: once you break the light barrier, time reverses polarity and shoots you from the hole. And a hypothetical engine that achieves FTL without time paradoxes does so by changing the curvature of space around you, again foiling the black hole. On the other hand, it's hard to predict in what exact time period of the universe will you arrive when you break free; most likely, you'll be lost in time. Oh, and, by the way, if you have a magical spaceship that just can accelerate to any velocity, you have an ability to kick physics in the nuts and take names, because screw you, Einstein. So why not just rip through the event horizon with your bare hands and march out, whistling Dixie?[[/note]]''

to:

''And it is getting closer.[[note]]Not exactly accurate. An engine that could achieve FTL by definition can reverse time and throw you into the past, that is, away from the hole. Just point yourself in ANY fucking direction and hit accelerate: once you break the light barrier, time reverses polarity and shoots you from the hole. And a hypothetical engine that achieves FTL without time paradoxes does so by changing the curvature of space around you, again foiling the black hole. On the other hand, it's hard to predict in what exact time period of the universe will you arrive when you break free; most likely, you'll be lost in time. Oh, and, by the way, if you have a magical spaceship that just can accelerate to any velocity, you have an ability to kick physics in the nuts and take names, because screw you, Einstein. So why not just rip through the event horizon with your bare hands and march out, whistling Dixie?[[/note]]''Dixie? (This Troper thinks you're full of shit. Correct me if I'm wrong, but wouldn't FTL travel mean nothing, if not even light can escape? So if it's faster than light, what difference does that make?)[[/note]]''
26th Jun '17 6:21:32 PM nombretomado
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Black holes normally can't be seen (thus their moniker), but there are ways they are detectable: if they are near another [[StarKilling star and siphoning off mass]], they can form accretion disks, which glow hot. There's gravitation lensing, in which black holes are detected by the image distortions of objects behind them (TheOtherWiki has a nice animation for that [[http://en.wikipedia.org/wiki/File:BlackHole_Lensing.gif here]]). And then there's Hawking radiation, which basically is a way for black holes to radiate stuff (by quantum mechanics), and is a whole other can of non-zero entropy worms. One of its more practically relevant attributes is that a black hole loses mass/energy this way - the ''smaller it is, the faster it goes''! In other words, really small ones, like the ones that the Large Hadron Collider might produce, would just evaporate and be gone before you even notice them (although the immense release of energy from the Hawking radiation would be noticeable). A sun-mass black hole, on the other hand, would lose about a milligram of its mass-energy every 3.1 x 10[[superscript:31]] (31 nonillion) years, which they'd more than make up for by consuming the cosmic microwave background. A [[http://arxiv.org/abs/0908.1803v1 scientific paper]] proposes to use a small artificial black hole's Hawking radiation as a means to convert mundane matter into energy and thrust to power a spaceship.

to:

Black holes normally can't be seen (thus their moniker), but there are ways they are detectable: if they are near another [[StarKilling star and siphoning off mass]], they can form accretion disks, which glow hot. There's gravitation lensing, in which black holes are detected by the image distortions of objects behind them (TheOtherWiki (Wiki/TheOtherWiki has a nice animation for that [[http://en.wikipedia.org/wiki/File:BlackHole_Lensing.gif here]]). And then there's Hawking radiation, which basically is a way for black holes to radiate stuff (by quantum mechanics), and is a whole other can of non-zero entropy worms. One of its more practically relevant attributes is that a black hole loses mass/energy this way - the ''smaller it is, the faster it goes''! In other words, really small ones, like the ones that the Large Hadron Collider might produce, would just evaporate and be gone before you even notice them (although the immense release of energy from the Hawking radiation would be noticeable). A sun-mass black hole, on the other hand, would lose about a milligram of its mass-energy every 3.1 x 10[[superscript:31]] (31 nonillion) years, which they'd more than make up for by consuming the cosmic microwave background. A [[http://arxiv.org/abs/0908.1803v1 scientific paper]] proposes to use a small artificial black hole's Hawking radiation as a means to convert mundane matter into energy and thrust to power a spaceship.
31st Jan '17 8:28:27 AM kwsn
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-->-- [=RobotRollCall=], [[http://www.reddit.com/r/askscience/comments/f1lgu/what_would_happen_if_the_event_horizons_of_two/ here]].

to:

-->-- [=RobotRollCall=], [[http://www.reddit.com/r/askscience/comments/f1lgu/what_would_happen_if_the_event_horizons_of_two/ here]].
here]], now with [[https://www.youtube.com/watch?v=-kVsxVBz1Mg audio]].
22nd Nov '16 5:20:26 PM darkzonork
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Another useful note is that black holes are one of the predictions derived from Einstein's theory of general {{UsefulNotes/relativity}} - and even in its context certain theorists saw the predictions of black holes in relativity and [[http://arxiv.org/abs/gr-qc/0412058 expressed doubts]] at least about the classical model. One such theorist was, initially, Einstein himself, who rejected the premise of a black hole rather strongly. Black holes just didn't make sense, especially how they muck up the nice wonderful understanding of space and time we (think) have.

to:

Another useful note is that black holes are one of the predictions derived from Einstein's theory of general {{UsefulNotes/relativity}} - and even in its context certain theorists saw the predictions of black holes in relativity and [[http://arxiv.org/abs/gr-qc/0412058 expressed doubts]] at least about the classical model. One such theorist was, initially, Einstein himself, who rejected the premise of a black hole rather strongly. Black holes just didn't make sense, especially how they muck up the nice wonderful understanding of space and time we (think) (think we) have.
22nd Nov '16 5:19:19 PM darkzonork
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Another useful note is that black holes are one of the predictions derived from Einstein's theory of general {{UsefulNotes/relativity}} - and even in its context certain theorists saw the predictions of black holes in relativity and [[http://arxiv.org/abs/gr-qc/0412058 expressed doubts]] at least about the classical model. One such theorist was, initially, Einstein himself, who rejected the premise of a black hole rather strongly. Black holes just didn't make sense, especially how they muck up the nice wonderful understanding of space and time we (think we) have.

to:

Another useful note is that black holes are one of the predictions derived from Einstein's theory of general {{UsefulNotes/relativity}} - and even in its context certain theorists saw the predictions of black holes in relativity and [[http://arxiv.org/abs/gr-qc/0412058 expressed doubts]] at least about the classical model. One such theorist was, initially, Einstein himself, who rejected the premise of a black hole rather strongly. Black holes just didn't make sense, especially how they muck up the nice wonderful understanding of space and time we (think we) (think) have.
20th Oct '16 5:01:23 PM ScorpiusOB1
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* Magic: Black holes don't gain any super-magic powers of suction when they become black holes. Their mass exerts the same gravitational force as a star, planet, or any other object of the same mass. If our sun were suddenly turned into a black hole, nothing would happen to us. [[note]] other than the fact that all that energy normally radiated from the sun is suddenly gone[[/note]] Well, nothing would happen to the planet, though we'd most likely die off from cold and starvation. If we wanted to study a black hole, we could put a probe in orbit around it the same way we put probes around other astronomical bodies. It's not going to instantly spiral to its doom (at least not any faster than it would around anything else)[[note]]However, since a black hole is ''far'' smaller than a star and does not emit radiation except very faint Hawking radiation, the probe could orbit it much closer. Tidal forces aside, if it's too close to the hole then itcould destroy the probe, so if it orbits very close, it could be unable to leave its orbit unless it had a very powerful engine.[[/note]]

to:

* Magic: Black holes don't gain any super-magic powers of suction when they become black holes. Their mass exerts the same gravitational force as a star, planet, or any other object of the same mass. If our sun were suddenly turned into a black hole, nothing would happen to us. [[note]] other than the fact that all that energy normally radiated from the sun is suddenly gone[[/note]] Well, nothing would happen to the planet, though we'd most likely die off from cold and starvation. If we wanted to study a black hole, we could put a probe in orbit around it the same way we put probes around other astronomical bodies. It's not going to instantly spiral to its doom (at least not any faster than it would around anything else)[[note]]However, else)[[note]]However since a black hole (except very massive ones) is ''far'' smaller than a star and does not emit radiation except very faint feeble Hawking radiation, the probe could orbit it much closer. Tidal be orbiting one at relatively close distances. However tidal forces aside, if it's too close to aside that could destroy said probe unless the hole then itcould destroy was large enough to have weak ones, below a certain point the probe, so if it orbits very close, it could probe would be unable to leave its keep a stable orbit unless it had a very powerful engine.[[/note]]
and would need to use an engine in order not to fall into the black hole (once that engine's fuel is used up, said goodbye to it)[[/note]]
1st Oct '16 11:22:52 AM Morgenthaler
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To learn more cool facts about black holes, please read [[IrregularWebcomic David Morgan-Mar's]] [[TheRant rant]] [[http://www.irregularwebcomic.net/2175.html here]]. Or [[http://www.reddit.com/r/askscience/comments/f1lgu/what_would_happen_if_the_event_horizons_of_two/ this]] science question on Reddit. Seriously, they're awesome.

to:

To learn more cool facts about black holes, please read [[IrregularWebcomic [[Webcomic/IrregularWebcomic David Morgan-Mar's]] [[TheRant rant]] [[http://www.irregularwebcomic.net/2175.html here]]. Or [[http://www.reddit.com/r/askscience/comments/f1lgu/what_would_happen_if_the_event_horizons_of_two/ this]] science question on Reddit. Seriously, they're awesome.
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