Since she's be central to the plot of the Disney film "The Black Hole", would that make Black Hole-sensei a Disney Princess?
Both Black Hole Sensei and...I guess "M87-Sama" by default scream bloody murder to all stars. Having a Disney Princess villain would be a treat, wouldn't it?
ithekro said: Since she's be central to the plot of the Disney film "The Black Hole", would that make Black Hole-sensei a Disney Princess?
GMO said: Both Black Hole Sensei and...I guess "M87-Sama" by default scream bloody murder to all stars. Having a Disney Princess villain would be a treat, wouldn't it?
Makes a guest appearance in treasure planet too :D
The densest girl in the universe. But would she be denser than harem Protags?
The Swarzschild radius of a black hole is a linear function of its mass, whereas volume is a cubic function of radius. So a black hole gains volume faster than it gains mass, and larger black holes have a lower average density than smaller ones. M87* has an average density of about 170 kg/m^3, which is about one-sixth the density of water.
The Swarzschild radius of a black hole is a linear function of its mass, whereas volume is a cubic function of radius. So a black hole gains volume faster than it gains mass, and larger black holes have a lower average density than smaller ones. M87* has an average density of about 170 kg/m^3, which is about one-sixth the density of water.
Arcana55 said:
The Swarzschild radius of a black hole is a linear function of its mass, whereas volume is a cubic function of radius. So a black hole gains volume faster than it gains mass, and larger black holes have a lower average density than smaller ones. M87* has an average density of about 170 kg/m^3, which is about one-sixth the density of water.
The Swarzschild radius of a black hole is a linear function of its mass, whereas volume is a cubic function of radius. So a black hole gains volume faster than it gains mass, and larger black holes have a lower average density than smaller ones. M87* has an average density of about 170 kg/m^3, which is about one-sixth the density of water.
it would make sense if the actual radius/volume of a black hole wasn't litterally 0; the "volume" or "radius" you're talking about is the one of the event horizon, which isn't an actual corporeal entity but a phenomenon of light, the density of a black hole is always infinite because no matter (pun intended) it's mass, all of the mass is concentrated in an infinitely small, dimensionless point. BTW i've found that it's also a misconception that the size of the event horizon is always proportionnal to the mass of the black hole; i don't remember what are the other factors but there are other factors that can make the event horizon bigger or smaller than it should be. (i would guess the spin is one of those factors but don't quote me on that. don't ask me how the hell can a dimensionless single point have a spin either, i don't know lol, ask the professionnals, i'm just an amateur with interest in the subject)
it would make sense if the actual radius/volume of a black hole wasn't litterally 0; the "volume" or "radius" you're talking about is the one of the event horizon, which isn't an actual corporeal entity but a phenomenon of light, the density of a black hole is always infinite because no matter (pun intended) it's mass, all of the mass is concentrated in an infinitely small, dimensionless point
Black holes don't work that way.
Or rather, you're confusing the black hole itself (the 4-D region of space-time that nothing can escape from at least not in the short term without some funky timey-wimey 'magic' wormhole business going on), with its singularities. Yes, singularities, plural. One of them is the event horizon (technically a coordinate singularity, that goes away by changing the coordinate system), the other is at the center (apparently a real physical singularity). Pop science media and laypeople confuse all these three for each other all the time.
(And singularity technically just means "set of values where the mathematical model just blows up and become undefined". f(x) = 1/x? x=0 is a singularity.)
Though yes, because space-time just straight-up curls up and cry in the general vicinity of a black hole (the 4D region in space-time), it is hard to get meaningful definitions of volume and density for one. In... simple (ha!) terms, the volume of a black hole depends on what... timeframe you're looking it at. Or timeline. Basically a snapshot in time, really (at least if one ignores the rotation part), but you can get many different values for "volume" depending on how you're defining your coordinate system (how you're looking at it in time, chiefly).
Though, from the PoV of a distant observer (in a short period of time), which is to say, us sitting on Earth, just taking the Swarzschild radius and assuming a sphere is a good enough approximation. So Arcana55's point still holds.
And as for point sources of matter... you know that the electron is also (currently considered) a point particle, right? And quarks? And they both have mass? So, technically one can define them to have zero volume and infinite density too. But hey, they don't cause black holes or tear apart space-time (appreciably) just by merely existing!
...Because practically speaking, the internal 'volume' is a pointless measure. Instead you consider the 'volume' that the particle occupies. That is, a volume of (3-D) space where you have high probability of finding said point particle. Oh, let's so make it 99%, that's good enough. So an electron in the ground-state orbit of an hydrogen atom occupies a volume of ~10−30 m^3, which is a... good enough definition for most 'classical' purposes.
And what region of space within which you are certain to find the 'inner' singularity of a black hole? Bingo, the entire black hole itself, the whole warped space-time region. That's your volume of a black hole. And as mentioned, taking the Swarzschild radius and assuming a sphere is a good enough approximation (given certain caveats that I don't really plan on saying again).
stellademoness said:
BTW i've found that it's also a misconception that the size of the event horizon is always proportionnal to the mass of the black hole; i don't remember what are the other factors but there are other factors that can make the event horizon bigger or smaller than it should be. (i would guess the spin is one of those factors but don't quote me on that. don't ask me how the hell can a dimensionless single point have a spin either, i don't know lol, ask the professionnals, i'm just an amateur with interest in the subject)
It's not a misconception. it's how the "Swarzschild radius" is defined. Look it up. It's kinda like a lower bound. And for most back-of-the-envelope 'calculations' from the PoV of a distant observer (over a short period of time, etc. etc.), it's good enough.
As for spin, any spinning object has an effect on space-time. Yes, this includes you spinning a Beyblade top, or cosplaying a JoJo Steel Ball Run character, though the effect will be pretty preeetty negligible.. Or rather, any object with an angular momentum, whether actually spinning-according-to-the-common-dicitonary-definition or not. So this will affect the shape of the event horizon. Though if you want to bring in rotating Kerr black holes into it, well... it doesn't have a 'point' singularity in the center. Instead it's a ring!
Anyway, black holes, the entire region-of-warped-space-time-from-which-light-can't-even-escape (other than some minor caveats over a long period of time possibly involving exotic particles and wormholes) have angular momentum. So they have spin. They also usually, well, spin. Around an axis. Take a good enough telescope and you can even see it. Or just piggy-back on one of NASA's.
Point particles? They ALSO have spin. Though spin here means "intrinsic angular momentum' instead of "physical spinning around a fixed axis passing through the particle". If you've taken chemistry classes up to a certain point, this forms the whole basis of the Pauli Exclusion Principle for electrons, and explains why only two electrons can 'fit' within a single orbital. One spins 'up', the other spins 'down', and nuh-uh, they can't both spin in the same 'direction' at once (because 'magic' math that will take too many words to explain especially without LaTeX notation) .
TL;DR: General Relativity can be unintuitive, Special Relativity can be unintuitive, Quantum Mechanics can be unintuitive... and physicists starting from the Einstein era are 'bad' at coming up with names.
*STARES AT "CHARM" AND "STRANGE" QUARKS* (Yes, that's what they are called.)