Does a Black Hole Have a Shape? 108
StartsWithABang writes: When you think about a black hole, you very likely think about a large amount of mass, pulled towards a central location by the tremendous force of gravity. While black holes themselves may be perfectly spherical (or for rotating black holes, almost perfectly spherical), there are important physical cases that can cause them to look tremendously asymmetrical, including the possession of an accretion disk and, in the most extreme case, a merger with another black hole.
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Too many goatse links?
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No. Too many medium.com links.
Yay meaningless prattle on unreadable hipster site (Score:2, Informative)
Time for some physics lectures by an actual physicst instead!
For example, start here [cosmolearning.org].
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WTF is "geek culture"?
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I thought that came along with being part of the Nerd Herd...
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I think you have Nerd [geekandnerdculture.com] and Geek [thinkgeek.com] culture mixed up with plain Geeks [peopleofwalmart.com].
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WTF is "geek culture"?
Nowadays, it means wearing heavy framed glasses with non-prescription lenses, and watching shitty bands on your Mac laptop in a coffee shop, i.e. it's a subset of hipsterdom, but with ironically bad haircuts instead of ironically bad facial hair.
A further subset is teenage girls who, like, read a book once and are randomly quirky.
Some doubts (Score:2)
Re:Some doubts (Score:4, Informative)
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Re:Like a dice (Score:5, Funny)
Die.
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Sheesh that's a little harsh.
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"Die" is the singular form of "Dice".
"Dice" is plural.
Re: Like a dice (Score:1)
Whoosh.
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I wasn't sure if I should reply with the correct answer or "whoosh" myself.
Kind of hard to tell if people feel the need to iterate a joke or are genuinely oblivious.
I went with the former. My mistake I suppose.
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I was going to say 'fuck off' but 'Die.' is better.
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I was going to say 'fuck off' but 'Die.' is better.
Well you could have said fuck off and Dice. I hear that's twice as insulting.
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Fuck off, Dice.
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Get free satoshi (Bitcoin) [goo.gl] and Dogecoins [goo.gl]
Just out of curiosity - are you still 'mining' for digital coins?
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I'm still getting a few referrals from time to time.
I only ever mined Dogecoins months ago, I was way too late in the game to mine Bitcoins.
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I'm still getting a few referrals from time to time.
I only ever mined Dogecoins months ago, I was way too late in the game to mine Bitcoins.
Totally agree, I did it a few years ago to try it out however once I calculated electricity costs and having to buy and update asics all the time, it didn't look like a game you could profit from.
Thanks!
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trashdot is at it again (Score:3, Insightful)
This is literally the dumbest fucking question I've ever seen in a slashdot article header. Fuck you slashdot, you're getting stupid to the point of being insulting.
Re:trashdot is at it again (Score:5, Informative)
I don't know, What Interesting Things Can I Power With an External USB Battery? [slashdot.org] comes pretty close.
But yes, this is pretty bad. And if you click through to the article, you'll find that it's every bit as moronic as the summary makes it sound.
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I'm pretty sure a black hole is shaped like a pair of butt cheeks, with hands spreading it apart...
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This is literally the dumbest fucking question I've ever seen in a slashdot article header. Fuck you slashdot, you're getting stupid to the point of being insulting.
Potty mouth zero-content sniping comments and Dice troll crap. Do they come in spray cans these days? So a science article [medium.com] has stunning visuals and not a single damned equation, like some of the boring games discussed around here. Back inside your Schwarzschildlike radius!
Of course it is relevant and interesting to speculate what black holes look like. It's primal because they're the most perilous things yet conceived and yet no one has actually 'seen' one. Even more disturbing, the physics claims we never
Re:trashdot is at it again (Score:4, Insightful)
Potty mouth zero-content sniping comments and Dice troll crap.
I absolutely agree that GP's comment is a bit of hyperbole. But that doesn't mean he doesn't have something of a point.
So a science article has stunning visuals and not a single damned equation
I'm okay with nice visuals if they're advertised and discussed clearly. They're not here.
Of course it is relevant and interesting to speculate what black holes look like.
Except that's not what the title or TFS implies. They ask "Do black holes have a shape?" And the answer is clearly simple -- spherical or nearly so.
Done.
Posing that question to anyone who knows anything about science probably would cause a reader to wonder -- "Hmm, are there more exotic shapes to black holes I haven't thought of? Why would those exist?"
But TFA is not about that -- in fact, it's about basic phenomena that anyone who knows anything about black holes would already be familiar with, like accretion disks and the fact that light gets distorted around black holes.
TFA is not actually about the shape of black holes themselves. It's about the shape of other phenomena that occur around black holes, or the temporary shifts in such phenomena when black holes merge or whatever. And while it has pretty pictures, nobody who has even read one book on pop science astronomy will learn any new facts from it.
(And, oddly, TFA isn't aimed at a new audience either, since it doesn't really explain basic facts like why we see the accretion disk but not the black hole or anything basic like that.)
It's primal because they're the most perilous things yet conceived and yet no one has actually 'seen' one. Even more disturbing, the physics claims we never could actually see them, only their effects. So we become curious about those effects. Not just from idle fancy, we instinctively feel the need to know how they may appear to us, no matter how unlikely that they would, because they are dangerous.
NO -- THEY ARE NOT "DANGEROUS."
You must be one of those people who think of black holes as some sort of giant vacuum cleaner going around and sucking up stuff around the universe. Sorry -- they don't work that way. They have gravity which works just like any other star or other large mass. You could have a stable orbit around them, for example (obviously at a safe distance).
They're only "dangerous" if you went inside one. But if that's your criteria, so are stars. So is the planet earth with its molten rock interior.
Your post is spreading the exact kind of ignorance that Slashdot should be committed to stomping out.
If TFA were an article that served as an intro to black holes and actually addressed some of that BS you're spouting about how "disturbed" everyone must be about things that are supposedly "dangerous," I'd be fine with that. But it's not. If TFA were an article that actually had some interesting noteworthy science about black holes, I'd be fine with that. But it's not.
And if TFA is just an article about pretty pictures (which it is), then just advertise it as such. And make the title accurate -- something like "What do we see when we look toward a black hole?"
TL;DR: THAT'S why GP is right to be upset -- not because the article is light on facts, but because it's misleading about the fact that it is uninformative (and only about pretty pictures), and it presents itself as tackling questions which it does not.
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.... which is exactly what I've come to expect from anything from "StartsWithABang", and particularly things where she only cites a "medium.com" source.
I'm trying to figure out a way of editing out her posts from my Slashdot headline feed. Any ideas?
[to be fair - she also has a post up which links to a couple of
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Yeah. Any idiot knows that half a hole is still a hole, black or not.
Hypothesis: Medium.com pays to Slashdot editors? (Score:1)
The interwebs... (Score:1)
...has ruined me.
Another one? (Score:5, Insightful)
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Maybe its time to stop reading /.
Looks up at your UID. But you just started! Why leave when we're having all this fun?
It's okay. If you stick around here long enough, you'll get jaded and cynical and fit in perfectly with the groupthink.
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Sheesh, I made a mod more offended than the person I was replying to? No sense of humor.
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Betteridge (Score:2)
says 'no'.
TL;DR (Score:2)
Does a Black Hole Have a Shape?
Black holes do have a shape!
Done.
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But every "picture" suggests things rotate about them in an accretion disk. Which doesn't make sense if they were all pulled in from different directions
It makes perfect sense when material isn't uniformly present in all directions, as in the case when a black hole pulls matter from an orbiting star.
Then there's the rotation of the black hole. That might have an influence such that an accretion disk will form in the plane perpendicular to the axis even if matter is infalling uniformly from all directions (this is just a guess).
So again, we're looking at observational error. It doesn't fit with our theory.
It doesn't fit with your theory. I'm not sure exactly what your theory is, though.
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... or from any other source where it has an inherent angular momentum, or has AM by the relative position of the accretion disc's matter source and the barycentre of the black hole.
The final shape of the accre
Re:TL;DR (Score:5, Insightful)
AFAIK: black holes are not sphere shaped, from our perspective - they're shell shaped. From our perspective as an outside observer, the singularity does not exist. From our perspective, time has slowed down on each particle moving into it from a near stop; they never actually pass the event horizon. Even the mass of the parent star that formed the black hole never reaches the event horizon as it is defined at the point in time that the star is collapsing, even though the event horizon may in time swell to a size that extends beyond where a collapsing particle was. Any light emitted from a doomed collapsing particle which manages ultimately escapes will do so on an escape trajectory that will always appear to come from outside the event horizon, no matter how much the black hole grew while it was in transit. From our external perspective, the particle never entered; the area beyond the event horizon is not part of spacetime to us. Now, as for an entity moving into the black hole, the perspective is different - the "hole" is quite well defined spacetime and they can enter just fine. But from our perspective, that entity never entered - it just slowed down to a virtual stop, stretched out across the event horizon.
Again, AFAIK, from my reading of the answer to the Hawking information paradox.
We love metrics that are continuous. We perceive the world with a Euclidean metric. And we generally don't have trouble understanding metrics distorted from the euclidean, such as the taxicab metric. Even the concept of a metric with points that bend space, simple gravitational distortion, is something we can usually grasp well after we get used to the concept. But people have trouble picturing a metric where space is warped by gravity so much that there exist regions where our euclidean mind insists must be there but actually aren't.
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When it gets close, the light is redshifted (still "blackbody", but shifted down). Just as if it were much colder. And radiating far less (as per Stephan's law). Therefore it will look black. Compared to the ~3K of the empty universe, the black hole at the event horizon is practically zereo K.
Which means blacker than space.
But still radiating.
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No, from an outside perspective it's never inside the event horizon. Only from the perspective of the matter entering the black hole does it cross. Saying "by then it's well within the event horizon" is simply not accurate from an outside perspective. No data collected from Earth will ever correspond to a reality in which the object has passed the event horizon.
Which is why there's no information paradox: the information is never in an unreachable state from any perspective.
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I think AC has you, at least in one sense; time approaches zero at the singularity, not at the event horizon.
Not sure if that makes a difference to the outside observer though.
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Numerous pages, including this one from NASA [nasa.gov], say that from an outside perspective it takes an infinite length of time for an object to cross the event horizon. Here's an "Ask a Physicist" column [io9.com] about black holes that says that time distortion reaches infinity at the event horizon. The Wikipedia article on event horizons says the same thing [wikipedia.org].
From our perspective, nothing ever passes the event horizon and thus the information is never lost.
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Right, from an outside perspective. But from the traveler's perspective, they pass right through without even noticing the event horizon.
I remember reading something that said roughly, that as you approach a singularity, that absolute time slows. In other words, it takes the lifetime of the universe for something to actually fall into the singularity. Which makes you wonder then, how there could be a singularity in the first place
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And from the traveler's perspective the universe is consistent and there's no information loss either. They still see an apparent horizon, a place where time appears to stop, but they never reach it, it always recedes ahead of them. To them, the area beyond that apparent horizon is also not part of spacetime, but nothing ever manages to enter it so no information appears to be lost.
They of course eventually get ripped apart by tidal forces, but their information doesn't disappear into a "no-hair" singularit
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An interesting side effect of this would be that it would actually be theoretically possible to send a probe into a black hole and get a signal back from it. If you're REALLY, REALLY, REALLY patient, that is ;)
(more realistically, one would likely try to probe the insides by making mciro black holes inside colliders and trying to get them to consume particles before they collapse, then looking for traces of information in the aftermath of the collapse)
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No signal could reach us from inside the event horizon. The probe could continue transmitting as it falls towards the event horizon, which will take forever from our point of view.
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Not forever, as black holes don't last forever. They evaporate due to Hawking radiation.
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So given the above, it's fair to assume then, that if time slows down to nearly nothing, then the object motion mus
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No, from an outside perspective it's never inside the event horizon. Only from the perspective of the matter entering the black hole does it cross. Saying "by then it's well within the event horizon" is simply not accurate from an outside perspective.
The problem is you're having this argument while not taking into account the problems with discussing "simultaneity" in general relativity. One might argue, by this logic, that black holes never really exist (even though we seem to observe them, or at least clear evidence of their effects), or that they could never grow (even though we could see them getting bigger in finite time).
While some people are happy to just argue for those things, e.g., that black holes never really exist, it gets at a deeper ep
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No, from an outside perspective it's never inside the event horizon. Only from the perspective of the matter entering the black hole does it cross. Saying "by then it's well within the event horizon" is simply not accurate from an outside perspective. No data collected from Earth will ever correspond to a reality in which the object has passed the event horizon.
The more I think about your post here, the more wrong it sounds to me. The only way to conclude that an object has passed the event horizon would be to observe the absence of radiation from that object. And that definitely occurs in finite time, since photons are discrete. See here [ucr.edu], which offers the following explanation:
Now, this led early on to an image of a black hole as a strange sort of suspended-animation object, a "frozen star" with immobilized falling debris and gedankenexperiment astronauts hanging above it in eternally slowing precipitation. This is, however, not what you'd see. The reason is that as things get closer to the event horizon, they also get dimmer. Light from them is redshifted and dimmed, and if one considers that light is actually made up of discrete photons, the time of escape of the last photon is actually finite, and not very large. So things would wink out as they got close, including the dying star, and the name "black hole" is justified.
As an example, take the eight-solar-mass black hole I mentioned before. If you start timing from the moment the you see the object half a Schwarzschild radius away from the event horizon, the light will dim exponentially from that point on with a characteristic time of about 0.2 milliseconds, and the time of the last photon is about a hundredth of a second later. The times scale proportionally to the mass of the black hole. If I jump into a black hole, I don't remain visible for long.
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They sort of do, but they're so distorted from our perspective as to be unrecognizable. Matter entering a black hole appears progressively more stretched out across its event horizon and doppler shifted.
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Another one that I see a lot of people having trouble with: that of there being a universal speed limit. I'm surprised at how many people think this means there's a speed limit from all perspectives.
If we launch some incredible 100fold-staged antimatter spacecraft capable of reaching 0.999c toward Alpha Centauri 4,3 light years away, from the perspective of people on Earth, it'll never reach or exceed c and will take a touch over 4,3 years to get there. But from the perspective of people onboard the spacecr
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This is not only incorrect, but impossible. If my time is speeding up and I'm looking at your watch, it's going to appear to be slowing down, and vice versa. Two parties both slowing down will appear indistinguishable from either party, rendering the concept of time dilation pointless.
The rest of what you wrote is what I wrote, just phrased differently: that from the perspective
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This is ridiculous. Even "at the most superficial level introduction of relativity "you should know that if a person departs earth moving at "nearly C" and comes back, far less time will have past for them than someone who stayed on Earth the whole time.
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The twin in the rocket ship turns and heads back to Earth, and you can tell from the inertia. The rocket ship feels acceleration as it changes course, and the Earth doesn't. The Earth twin stays in the same (roughly) inertial reference frame, while the spaceship one switches frames.
It is possible to have multiple paths that meet again without any of them experiencing acceleration, but at that point we have to rely on general relativity, and frankly I don't understand it well enough.
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At no time does anything seem to be going faster than light from any perspective. If we had a magical power source and a magical way to accelerate everything in the spaceship at once*, then, yes, it could go to Alpha C that fast from the crew's perspective. The crew would observe the distance to be over 4 light years before starting and after decelerating at the target, but a vastly shortened distance while in transit.
*When we're talking about these speeds, "at once" gets rather fuzzy. I mean at once
black hole != singularity (Score:2)
so you get situations that can distort the shape of the event horizon or accretion disk(s), .. that is nice, but those are not black holes, they are just related phenomena
so you get to the point where you think your knowledge about black holes makes you an expert, but then you find out that you confused black holes with singularities.
StartsWithABan.... TL;DR (Score:3)
Wow it's amazing but I lost interest reading TFS at the very first word.
It's amazing how quickly Slashdot is able to convey meaning in a summary. Only one word in and I know everything I ever need to know about the post.
Extremely poor article on black holes (Score:2)
When an essay or article has statements ike this:
A black hole is therefore a region of space that is totally, utterly dominated by the force of gravity.
It's clear the author knows little to nothing about physics. The physics _inside_ a black hole is local and can be quite normal: there's no reason to think it's _not_ normal physics. The definition of black holes involves the net effect of gravitation _outside_ the black hole, with a net escape
Shaped like .... (Score:2)
There goes the planet... (Score:2)
Does a black hole have a shape? (Score:1)
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