black holes
May 4, 2006 6:35 AM
What does a black hole look like?
From where?
posted by planetkyoto at 6:52 AM on May 4, 2006
posted by planetkyoto at 6:52 AM on May 4, 2006
I think it literally looks like a black hole in space. Any nearby stars have their gas sucked off them, and that swirls around a black center.
posted by Orange Goblin at 6:52 AM on May 4, 2006
posted by Orange Goblin at 6:52 AM on May 4, 2006
Actually the wikipedia article I linked to has a simulated picture.
posted by ludwig_van at 6:55 AM on May 4, 2006
posted by ludwig_van at 6:55 AM on May 4, 2006
IANAPhysicist. But I do read lots of SF and read and watch lots of science stuff.
Unless they've lied to me:
A big black hole -- the kind you think about when you think of a black hole -- would look like a glowing donut. A big glowing disc of stuff (the accretion disc) spinning around an empty core (the hole itself).
A little one, with the mass of a mountain, might look like a little spark or glow dimly like hot iron from the Hawking radiation as it evaporates.
posted by ROU_Xenophobe at 7:05 AM on May 4, 2006
Unless they've lied to me:
A big black hole -- the kind you think about when you think of a black hole -- would look like a glowing donut. A big glowing disc of stuff (the accretion disc) spinning around an empty core (the hole itself).
A little one, with the mass of a mountain, might look like a little spark or glow dimly like hot iron from the Hawking radiation as it evaporates.
posted by ROU_Xenophobe at 7:05 AM on May 4, 2006
What you will see is many objects moving very quickly to a certain, dark spot in space. But the visible properties of these objects change in dramatic ways close to black holes.
Let's say you face yourself right in front of the black hole. Let's also suppose that magically, you have no mass and thus are not dragged in by its gravitational field (Deep, dark magic, to be sure). See all those stars all around you? Well, they aren't where you think they are. (Of course, with relativity, its hard to talk about "where" something is without also discussing how long it would take to reach it. But that's neither here nor there.)
You see, since a black hole is so massive the light that stars emit is bent around it. So as you move away from the blackhole, the star that seemed to be really close to being at exactly your right hand side, can, in fact, be way in front of you and only a little bit to your right. This effect occurs around any massive body (from stars to ships to billiard balls) and, in 1918, this bending of light around the Sun was used as the first (but not last!) verification of general relativity.
I would be remiss to ignore the redshifting of light coming from objects accelerating to you. Basically, as objects accelerate (remember acceleration = change in velocity per unit of time) away we view the light coming off of them as being more "red" than if it were standing still. When objects accelerate towards us, we view them as more "blue". Now, gravitationaly fields are exactly like acceleration fields, so this same shifting of color happens when objects are pulled into blackholes, or pulled towards any object with mass. It's just we don't notice it because the objects we are used to dealing with like computers and cups and planes and space stations don't have a lot of mass, and the effect is small.
I probably typed somethings out wrong, but I've got a quantum mechanics final to worry about first. Hope this helps!
posted by jmhodges at 7:06 AM on May 4, 2006
Let's say you face yourself right in front of the black hole. Let's also suppose that magically, you have no mass and thus are not dragged in by its gravitational field (Deep, dark magic, to be sure). See all those stars all around you? Well, they aren't where you think they are. (Of course, with relativity, its hard to talk about "where" something is without also discussing how long it would take to reach it. But that's neither here nor there.)
You see, since a black hole is so massive the light that stars emit is bent around it. So as you move away from the blackhole, the star that seemed to be really close to being at exactly your right hand side, can, in fact, be way in front of you and only a little bit to your right. This effect occurs around any massive body (from stars to ships to billiard balls) and, in 1918, this bending of light around the Sun was used as the first (but not last!) verification of general relativity.
I would be remiss to ignore the redshifting of light coming from objects accelerating to you. Basically, as objects accelerate (remember acceleration = change in velocity per unit of time) away we view the light coming off of them as being more "red" than if it were standing still. When objects accelerate towards us, we view them as more "blue". Now, gravitationaly fields are exactly like acceleration fields, so this same shifting of color happens when objects are pulled into blackholes, or pulled towards any object with mass. It's just we don't notice it because the objects we are used to dealing with like computers and cups and planes and space stations don't have a lot of mass, and the effect is small.
I probably typed somethings out wrong, but I've got a quantum mechanics final to worry about first. Hope this helps!
posted by jmhodges at 7:06 AM on May 4, 2006
If the black hole is near other objects, it will distort the paths of those objects. Some may orbit around it - if there isn't any matter falling into the black hole, then you'll see things orbiting what appears to be empty space. If stuff *is falling in then there will be all kinds of emission all over the spectrum, so what the black hole looks like depends on what wavelength you pick.
A black hole orbiting as part of a binary system with a visible star may pull a streamer of material off of the companion, resulting in the dramatic spectacle of a star with a curved, spiral 'tail' that eventually is consumed by the invisible companion.
Finally, if there is a black hole in an 'empty' vacuum (as empty as space gets, anyway) there will still be gravitational lensing effects around the black hole as it bends light passing near it. The Hubble telescope found isolated black holes exhibiting this behaviour. A black hole may also be detectable by looking for particle creation at the event horizon, as Hawking theorized.
posted by Dipsomaniac at 7:20 AM on May 4, 2006
A black hole orbiting as part of a binary system with a visible star may pull a streamer of material off of the companion, resulting in the dramatic spectacle of a star with a curved, spiral 'tail' that eventually is consumed by the invisible companion.
Finally, if there is a black hole in an 'empty' vacuum (as empty as space gets, anyway) there will still be gravitational lensing effects around the black hole as it bends light passing near it. The Hubble telescope found isolated black holes exhibiting this behaviour. A black hole may also be detectable by looking for particle creation at the event horizon, as Hawking theorized.
posted by Dipsomaniac at 7:20 AM on May 4, 2006
Cygnus X-1 is believed to be a black hole that is in the process of dismantling a neighboring star. You can see the hot gas from the star being pulled aside as it forms the black hole's accretion disk.
posted by kaseijin at 7:42 AM on May 4, 2006
posted by kaseijin at 7:42 AM on May 4, 2006
Things that you can see either generate or reflect light. If an object does neither of those things, there's nothing to see, and your eyes give a corresponding blank area.
Your brain shows areas with no stimuli from your eyes as black, even though we can see some black objects because they reflect light.
For instance, I have a black PC here. I can see it, because both the glossy and matte surfaces of it reflect light.
But a black hole neither generates nor reflects light. Your eyes have no data to process, so your brain puts black there.
posted by SlyBevel at 8:37 AM on May 4, 2006
Your brain shows areas with no stimuli from your eyes as black, even though we can see some black objects because they reflect light.
For instance, I have a black PC here. I can see it, because both the glossy and matte surfaces of it reflect light.
But a black hole neither generates nor reflects light. Your eyes have no data to process, so your brain puts black there.
posted by SlyBevel at 8:37 AM on May 4, 2006
i think the drawings are wrong... the gases would not be circulating so much like a disk as a sphere... the uniform distribution would kind of create a strange fuzzy spherical blur instead of a doughnut... right? It's just too convenient to assume that gas would come in and ring around it leaving a neat little visible black hole
posted by trinarian at 9:04 AM on May 4, 2006
posted by trinarian at 9:04 AM on May 4, 2006
The question is, how much more black could it be? And the answer is, none. None more black.
posted by GregW at 9:35 AM on May 4, 2006
posted by GregW at 9:35 AM on May 4, 2006
i think the drawings are wrong... It's just too convenient to assume that gas would come in and ring
No. It's an accretion disc.
posted by event at 9:54 AM on May 4, 2006
No. It's an accretion disc.
posted by event at 9:54 AM on May 4, 2006
Some black holes are pink. (Technically the pink hue comes from gases surrounding the black hole)
posted by justkevin at 10:16 AM on May 4, 2006
posted by justkevin at 10:16 AM on May 4, 2006
I heard they were green, but that could be totally made up. I like the idea that they're pink better.
posted by dagnyscott at 10:33 AM on May 4, 2006
posted by dagnyscott at 10:33 AM on May 4, 2006
dagnyscott: The idea that black holes are green refers to their efficiency when thought of as engines, not their appearance.
Source here, from The Register
trinarian: Tidal forces align the rotation of material to the rotational direction of the black hole itself, thus making a disc of material in one plane around the black hole.
posted by Third at 11:18 AM on May 4, 2006
Source here, from The Register
trinarian: Tidal forces align the rotation of material to the rotational direction of the black hole itself, thus making a disc of material in one plane around the black hole.
posted by Third at 11:18 AM on May 4, 2006
Related: collision of 2 black holes.
I highly recommend to watch the mpeg movie: beauty.
posted by bru at 11:46 AM on May 4, 2006
I highly recommend to watch the mpeg movie: beauty.
posted by bru at 11:46 AM on May 4, 2006
Until recently the prevailing opinion on the appearance of black holes was "nature abhors a naked singularity." In other words, a black hole can not be observed directly, only by it's effects on the environment around it, such as the examples given above. However, Stephen Hawking recently recanted his earlier opinion and has decided that information can in fact escape form a black hole. This would imply that, at least according to Hawking, a black hole can be observed directly.
posted by lekvar at 12:52 PM on May 4, 2006
posted by lekvar at 12:52 PM on May 4, 2006
As near as I can understand, the strict answer to the question involves unsolved questions relating to quantum gravity, which is indeed Hawking's baby.
One problem is that, in the current schema, rotating black holes warp space-time, locally, in such a way that it is possible for an observer to approach the event horizon of a black hole, then accelerate away, well outside the Schwarzchild radius, but within the ergosphere, having gained energy from the black hole in the encounter (and having made the black hole's spin slow down by the same amount of energy.)
This implies that energy, and hence information, can in fact leave a black hole, which implies some method of the energy getting out of the black hole (quantum tunnelling? quintessential radiation?). And if energy can leave a black hole somehow, presumably that phenomenon could be observed in such a way as to tell us something about the black hole in question. That means that the black hole must be able to "look like" something, not nothing.
No one seems able to agree on what that something is, though. As soon as I can condense this very interesting text file about gamma-ray bursts I've been writing into a paragraph or two, I'll make an FPP out of it.
posted by ikkyu2 at 8:00 PM on May 4, 2006
One problem is that, in the current schema, rotating black holes warp space-time, locally, in such a way that it is possible for an observer to approach the event horizon of a black hole, then accelerate away, well outside the Schwarzchild radius, but within the ergosphere, having gained energy from the black hole in the encounter (and having made the black hole's spin slow down by the same amount of energy.)
This implies that energy, and hence information, can in fact leave a black hole, which implies some method of the energy getting out of the black hole (quantum tunnelling? quintessential radiation?). And if energy can leave a black hole somehow, presumably that phenomenon could be observed in such a way as to tell us something about the black hole in question. That means that the black hole must be able to "look like" something, not nothing.
No one seems able to agree on what that something is, though. As soon as I can condense this very interesting text file about gamma-ray bursts I've been writing into a paragraph or two, I'll make an FPP out of it.
posted by ikkyu2 at 8:00 PM on May 4, 2006
Here is another image similar to the wikipedia one that might help you imagine a black hole
posted by thandi at 1:46 PM on May 5, 2006
posted by thandi at 1:46 PM on May 5, 2006
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"The gravitational field is so strong that the escape velocity past its event horizon exceeds the speed of light. This implies that nothing, not even light, inside the event horizon can escape its gravity."
posted by ludwig_van at 6:44 AM on May 4, 2006