Does a Black Hole Have a Shape?

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.

Comments

Yay meaningless prattle on unreadable hipster site

[Anonymous Coward]

Time for some physics lectures by an actual physicst instead!

For example, start here.

trashdot is at it again

[Anonymous Coward]

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

[aardvarkjoe]

I don't know, What Interesting Things Can I Power With an External USB Battery? 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.

Re:trashdot is at it again

[AthanasiusKircher]

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.

Re:Like a dice

[Tukz]

Die.

Another one?

[Pubstar]

Another SWAB post? In under a day? Maybe its time to stop reading /.

Re:Like a dice

[Anonymous Coward]

Sheesh that's a little harsh.

Re: Like a dice

[Whiteox]

I was going to say 'fuck off' but 'Die.' is better.

StartsWithABan.... TL;DR

[thegarbz]

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.

Re:TL;DR

[Rei]

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.

Re:TL;DR

[Rei]

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 spacecraft, they're reaching their destination in only 70 days. From our perspective, their time slows down 22,4-fold; from theirs, Earth time has speed up. We see their velocity as capped off at c; to them, it's as if they can just keep accelerating without limit.

Now, it's not exactly like "going really fast"; everything around them seems pinched toward the forward direction and shifted to blue, like this - the same situation as where we see light emitted from particles moving at relativistic speeds relative to us (such as a black hole's event horizon) doppler shifted and distorted. If the occupants of our spacecraft go fast enough, even the cosmic microwave background will be shifted into the visible spectrum. ;)

Re: TL;DR

[Rei]

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.

Re: Like a dice

[ArcadeMan]

Fuck off, Dice.

Re:Some doubts

[pollarda]

Actually, a good friend of mine Dave Nielson (professor BYU) did his PhD at the University of Texas on this very subject -- sort of. (His PhD was on what happens when two black holes collide.) So I asked him what happens when they collide and he said that they deform. The orbiting black hole and the central black hole both deform in the way you would expect. After they collide, they merge and the whole thing wobbles. (Think water or oil drops in zero G.) I left unimpressed -- not because he didn't do great work but, black holes deform under gravity and exhibit all the properties you would expect with regular fluids when they are attracted to each other or collide..