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

Please stop

[Anonymous Coward]

..please just stop.

Re:Please stop

[Tablizer]

Too many goatse links?

Re:Please stop

[OolimPhon]

No. Too many medium.com links.

Yay meaningless prattle on unreadable hipster site

[Anonymous Coward]

Time for some physics lectures by an actual physicst instead!

For example, start here.

Like a dice

[Anonymous Coward]

Yes black holes are shaped like a dice. It is a well known fact.

Re:Like a dice

[Tukz]

Die.

Re:Like a dice

[Anonymous Coward]

Sheesh that's a little harsh.

Re:Like a dice

[Tukz]

"Die" is the singular form of "Dice".
"Dice" is plural.

Re: Like a dice

[Anonymous Coward]

Whoosh.

Re: Like a dice

[Tukz]

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.

Re: Like a dice

[Whiteox]

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

Re: Like a dice

[MrKaos]

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.

Re: Like a dice

[Anonymous Coward]

That will depend on the number you get after you throw the die.

Re: Like a dice

[ArcadeMan]

Fuck off, Dice.

Re:Like a dice

[__aaclcg7560]

Not when you hit the event horizon.

Re: Like a dice

[MrKaos]

Get free satoshi (Bitcoin) [goo.gl] and Dogecoins [goo.gl]

Just out of curiosity - are you still 'mining' for digital coins?

Re: Like a dice

[ArcadeMan]

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.

Re: Like a dice

[MrKaos]

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!

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

[Noah Haders]

I'm pretty sure a black hole is shaped like a pair of butt cheeks, with hands spreading it apart...

Re:trashdot is at it again

[TheRealHocusLocus]

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 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 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.

Imagine the night illuminated by a house being completely consumed by fire, explosions, steam rising as jets from fire hoses sweep across its blackened face and through windows. Children splash in the puddles, step over hoses. People stand transfixed... why? And almost no one is clustered around the physicist who has set up a portable chalkboard on the corner and is trying to describe the exothermic process of combustion in real-time. They are interested, sure, but there will be time for that later. As the terrifying monster rages they must look, see it through to the end, because we are curious, intelligent resourceful beings and must look directly into the eyes of the Enemy.

Re:trashdot is at it again

[Anonymous Coward]

Pessimist. I don't feel as guilty trolling Stupid questions. We need a national holiday for dumb people, that way we can say, "please hold your questions till idiot day".
  waiting four years to express your opinion in a presidential election isn't working.

Re:trashdot is at it again

[Anonymous Coward]

No, that's just the event horizon. Don't look too deep into the center or it will swallow you.

Re:trashdot is at it again

[ArcadeMan]

Yeah. Any idiot knows that half a hole is still a hole, black or not.

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:trashdot is at it again

[Anonymous Coward]

Um, no. Half a black hole could very likely be a star. Not a hole, not black.

Re:trashdot is at it again

[Anonymous Coward]

Its better than the garbage video game articles we've been seeing.

You want to see better articles, submit them.

Re:trashdot is at it again

[RockDoctor]

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.

.... 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 other sources which are not medium. Which ameliorates my standing suspiscion that they're an account owned by Medium.com's advertising agency. Slightly ameliorates.]

Hypothesis: Medium.com pays to Slashdot editors?

[Anonymous Coward]

Just a hypothesis.

The interwebs...

[abednegoyulo]

...has ruined me.

Another one?

[Pubstar]

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

Re:Another one?

[weilawei]

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.

Re:Another one?

[Pubstar]

I actually cant remember the password to my old account due to the fact that I stopped reading for a bit. I was pretty active like 2004-ish.

Re:Another one?

[weilawei]

Sheesh, I made a mod more offended than the person I was replying to? No sense of humor.

/karma-burner fueled and ready to go.

Re:Another one?

[Anonymous Coward]

I actually cant remember the password to my old account due to the fact that I stopped reading for a bit. I was pretty active like 2004-ish.

And like me it's probably tied to an old defunct free email account so retrieving the password is impossible.

Re:Another one?

[Pubstar]

The fact that you called them out on their group think made them angry.

Betteridge

[Livius]

says 'no'.

TL;DR

[wonkey_monkey]

Does a Black Hole Have a Shape?

Black holes do have a shape!

Done.

Re:TL;DR

[Guildor]

The article is trying to say it's sphere shaped. 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 (spherical influence of gravity). So again, we're looking at observational error. It doesn't fit with our theory. There are so many questionable observations with regards to black-holes, I think it needs a re-think. The article talks authoritatively, making assertions that only gravity can answer, but this isn't true either. To me, it's click-bait. Nothing new to learn here, and nothing getting us closer to the truth. Black holes are one accepted answer to what we think we see, but are there any other acceptable answers that match the same observations? Are we even looking at a black hole at all?

Re:TL;DR

[wonkey_monkey]

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.

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

[Anonymous Coward]

honest question from somebody with near zero astronomical knowledge:

if stuff looks like it never enters the black hole, shouldn't black holes look like katamari balls instead of black holes?

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

[Anonymous Coward]

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.

Re: TL;DR

[Anonymous Coward]

GP is wrong. Matter can easily pass the event horizon, which is just the point at which it can no longer escape. Gravity isn't nessecarilly even that extreme at an event horizon; you could fall in without noticing.

From an outside observer's perspective, infinite time dialation occurs as matter approaches the singularity itself, so matter will never actually hit it. But by then it's well within the event horizon.

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:TL;DR

[Rei]

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.

Re:TL;DR

[Anonymous Coward]

From our perspective, their time slows down 22,4-fold; from theirs, Earth time has speed up

No, from both perspectives it seems like the time of the other has slowed down, including Earth from the perspective of the ship.

I'm surprised at how many people think this means there's a speed limit from all perspectives.

Because it is under relativity. The only way you can make something look like it is going faster than c on non-cosmological scales is if you start pulling measurements from different perspectives (i.e. frames). It only looks like your going faster than c to Alpha Centari if you use the time from the perspective of the space ship and the distance from the perspective of the Earth. If you stayed consistent, length contraction from the perspective of the space ship makes the distance between Alpha Centari and Earth look much shorter, so they never exceed c in their perspective either. If you are just going to mix things from different frames, there is nothing stopping you from doing that now and finding a frame paired with Earth's frame that makes it look like Voyager 2, or even a car on a highway, look like it is going faster than light, but none of which will be consistently show that from measurements within a single frame.

Re: TL;DR

[towermac]

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.

Re: TL;DR

[Rei]

Numerous pages, including this one from NASA, 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 about black holes that says that time distortion reaches infinity at the event horizon. The Wikipedia article on event horizons says the same thing.

From our perspective, nothing ever passes the event horizon and thus the information is never lost.

Re:TL;DR

[Rei]

No, from both perspectives it seems like the time of the other has slowed down, including Earth from the perspective of the ship.

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 of the people on the ship, the 4,3 light year journey only takes 70 days. They are not capped in their rate of travel by some cosmic absolute "speed limit". Only to a third party to which they are moving relative will their velocity appear to be unable to reach or exceed c.

Re: TL;DR

[towermac]

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

Re: TL;DR

[Anonymous Coward]

, that absolute time slows.

Then whatever you were reading is not consistent with general relativity...

In other words, it takes the lifetime of the universe for something to actually fall into the singularity.

This doesn't happen in really applicable to any relevant frame. To the outside observer, the infalling thing slows as it approaches the horizon, not the singularity. In a falling frame, you hit the singularity in a finite and rather short time scale. Even if you have two things fall separated by a small distance, neither takes a long time to get there from each other's perspective.

Re:TL;DR

[Anonymous Coward]

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.

Have you never seen anything about the twin paradox? Even at the most superficial level introduction of relativity, you get that time slows down when something is moving relative to the observer. In this example, Earth is moving relative to the spaceship, so its time will be slowed compared to time observed in the frame of the spaceship. It is not impossible, because there is no absolute time, and no requirement that two parties in different frames agree on time measurements.

The rest of what you wrote is what I wrote,

Certainly not considering you wrote:

from the perspective of the people on the ship, the 4,3 light year journey only takes 70 days

From the perspective of the people on the ship, the journey is no longer a distance of 4.3 light years. If the spaceship is going 90% of c relative to Earth, then in the spaceship's frame it will take them 2.08 years to make that trip, and also in their frame they will observe it takes light 1.87 years to go from Earth to Alpha-Centari.

Re: TL;DR

[Rei]

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" singularity, it remains to be released when the black hole evaporates. As a black hole evaporates, time showing the particles falling deeper and deeper into it becomes observable to the outside world (albeit incredibly distorted and with the matter ripped to bits).

Again, that's at least my understanding of Hawking's "black holes don't actually exist" concept, and it makes logical sense to me. From the perspective of a traveler, they're just falling to their deaths in an extreme sort of collapsed star. From the perspective of an outside observer, they've fallen into a spot where a the collapsed star has ripped a hole in spacetime that won't start back up (from our perspective) until the "hole" boils off. Nothing ever lost, nothing ever undefined, always part of our universe, just effectively frozen temporarily in time. From our perspective.

Re: TL;DR

[Rei]

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)

Re: TL;DR

[AthanasiusKircher]

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 epistemological question of what sort of observation is necessary to prove something "exists." We infer the existence of a lot of things by their effects, even if we can't observe them directly. For very long periods of time, black holes do exist according to that latter definition.

No data collected from Earth will ever correspond to a reality in which the object has passed the event horizon.

That's true in the sense that there is no visible event of an object crossing the event horizon in finite time.

But, on the other hand, we can also observe changes in the black hole occurring in finite time (formation, growth, evaporation), which seems to imply actual travel across the event horizon. It's complicated to explain why both such things are possible, though this answer seems to get at some of the problems.

Which is why there's no information paradox: the information is never in an unreachable state from any perspective.

That's somewhat true, but it's a somewhat different question to determine what it means for a distant observer to judge "whether something is inside the event horizon." Do we mean:

(1) "I visually saw that thing go inside the event horizon" (false -- obviously, since the definitely of "event horizon" precludes observation of such a thing)

Or

(2) "That black hole appears bigger than it did a billion years ago, so it must have absorbed mass from that thing" (could be true)

Personally, I think (2) would count as "data collected from Earth [that] correspond[s] to a reality in which the object has passed the event horizon."

Re:TL;DR

[Rei]

Have you never seen anything about the twin paradox? Even at the most superficial level introduction of relativity, you get that time slows down when something is moving relative to the observer.

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.

From the perspective of the people on the ship, the journey is no longer a distance of 4.3 light years. If the spaceship is going 90% of c relative to Earth, then in the spaceship's frame it will take them 2.08 years to make that trip, and also in their frame they will observe it takes light 1.87 years to go from Earth to Alpha-Centari.

First off, apart from trying to add confusion, why did you change the velocity from the one I gave? Secondly, from a trip travel time perspective, it doesn't matter whether you view it as time dilation or length contraction. The trip at 0.999c takes 70 days from the perspective of the crew. That's the beginning and end of it right there. From their perspective, it's as if they got there moving far faster than the speed of light, as if there were no limits on how fast they could keep accelerating. With an infinite supply of energy, they could travel the 4,3 light years in what they perceive to be 7 days, 7 hours, 7 minutes, or 7 seconds (let's ignore G-forces here, or how to have such vast quantities of energy at their disposal). The crew of a spacecraft experiences no "upper limit" to how fast the universe will allow them to traverse a distance.

Re:TL;DR

[Anonymous Coward]

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.

Then you are speaking as if you've only heard of the twin paradox in some superficial way and never actually read about it. Heck, even the intro paragraph of Wikipedia article on the "paradox" (most paradoxes in physics aren't actual logical paradoxes...) quite clearly points out that both the twin on Earth and the twin traveling away see the other's time as slowed. The resolution has nothing to do with the clock on Earth looking like it is going faster to the traveler during constant velocity motion between end points.

From their perspective, it's as if they got there moving far faster than the speed of light

This never happens in any frame within relativity. They will still observe light to be going at the same speed, and getting from their origin to their destination in less time than it took them. You can't decouple time dilation and length contraction, they both happen together. In relativity, there is nothing special about distances measured from Earth's frame. Otherwise you get nonsensical results, like observing that light is traveling faster than light, and are likely to completely screw up issues related to simultaneity.

Re: TL;DR

[AthanasiusKircher]

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, 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.

Re:TL;DR

[Anonymous Coward]

Time stretches when you're leaving and compresses when you're coming. The twin 'paradox' appears when you make the U-turn to come back home.

Re:TL;DR

[Anonymous Coward]

From our perspective, their time slows down 22,4-fold; from theirs, Earth time has speed up

This is not how time dilation works. It doesn't care what direction you are going in, only the relative speed. Earth sees the spaceship traveling at 0.999c, and hence a time slowed to 4.5%. The spaceship sees earth traveling at 0.999c, and hence sees Earth's time slowed to 4.5%. There is no way to distinguish which frame is moving vs. not moving as there is no absolute frame of reference. Anything moving relative to you will have a time dilation appearing to slow down. You only can see time going faster for another point with acceleration/gravity.

Re:TL;DR

[Agent0013]

But wouldn't it be the Earth that is doing the U-turn and coming back at you? Seriously, if there is no preferred reference frame, then both twins could end up being younger than the other one depending on which frame you look at it from. So in the end they are the same age? I have never heard it told that way before though!

Re: TL;DR

[david_thornley]

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.

Re:TL;DR

[david_thornley]

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.

Re:TL;DR

[david_thornley]

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 from the point of view of the ship.

Re: TL;DR

[Anonymous Coward]

Prove it

Re: TL;DR

[Rei]

Not forever, as black holes don't last forever. They evaporate due to Hawking radiation.

Re: TL;DR

[Anonymous Coward]

You can see how wrong you are when considering the limit of supermassive black holes. At their (outer, Kerr) event horizons, space is gently curved enough that the gravitational redshift as infalling matter approaches the horizon from the outside is NEGLIGIBLE. Stars cleanly crossing the horizon of something more massive than Sag-A* will simply disappear from view for an Earthlike observer. (Stars in orbits very slightly more elliptical than the ISCO will be shredded apart, however it will not be because of spaghettification, and few massive objects will ever reach such an orbit anyway).

Re: TL;DR

[Anonymous Coward]

At their (outer, Kerr) event horizons, space is gently curved enough that the gravitational redshift as infalling matter approaches the horizon from the outside is NEGLIGIBLE.

Gravitational redshift is not a local function of curvature, but a global function that depends on the curvature over the whole path of the light. It doesn't matter how gentle curvature is at the source, and the red shift experienced as you approach the event horizon of a black hole is not a function of size or rotation speed of the black hole.

Re: TL;DR

[Guildor]

Picture this : A massive object that is partly inside the event horizon, partly outside, and approaching via rotation around the black hole. If time is exerted differently on the inside when compared to the outside (observable) then this means the part of the object on the inside must actually accelerate in velocity to keep pace with the remaining part of the object outside the black hole.

So given the above, it's fair to assume then, that if time slows down to nearly nothing, then the object motion must also approach the speed of light. But given that it takes infinite amounts of energy to achieve this, from where does the energy come?

Re: TL;DR

[Guildor]

Yeah, black holes collapsing. This doesn't make any sense! If infinite gravity, and infinite time exist in a black hole, they're a permanent fixture in time and space. I'm sure you've read some paper that talks about disappearing black holes, but perhaps it's more realistic there was never a black hole in the first place.

Re: TL;DR

[Guildor]

Does anyone know if gravity affects a radio wave? I don't think it does??

Re:TL;DR

[RockDoctor]

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.

... 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 accretion disc is then going to be a complex composite of the original matter's AM, and any torque imposed on it by the gravitational asymmetries in the region around the black hole. I don't have the maths to describe it, but that has been the empirical description for several decades - possibly up to 4 decades.

Re:Yay meaningless prattle on unreadable hipster s

[umghhh]

Basic course is, I think, not something that one could expect to be interesting for a /.er (ones that would need basic course, and there are many, would have to start with reading comprehension and basic maths first possibly augmented with basic philosophy). There are other courses and if one looks for entertainment like physics content I would look for something like this interview - it is interesting, not to deep for an afternoon after work and not too easy for a curious mind.

event horizon != black hole

[Anonymous Coward]

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

Does a Tholian Web Have a Shape?

[Anonymous Coward]

Yes, yes it does.

If you please, also consider this.

I think, therefore I am, I think.

Or for the funny-bone in you.

Turn to the next page.

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:StartsWithABan.... TL;DR

[Anonymous Coward]

Would be nice though if it was tagged with medium so I don't even have to click it.

black hole != singularity

[Rockoon]

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.

Yes

[Anonymous Coward]

But every time I try to draw the shape it keeps getting sucked in.

Re:Yes

[Anonymous Coward]

So, it's shaped like an egg?

Re:Yay meaningless prattle on unreadable hipster s

[Anonymous Coward]

This article (or at least purported in the summary--I've long since given up trying to read anything at the target site) deals with physics. Reading comprehension, writing, basic literacy, philosophy, math, and all that, sure have their place and need to be linked more since the submissions the editors let through indicate a distinct lack of (expected) depth (in the readership). This very serial poster is a case in point, since he's posting a fluffy mass of fluff posts about physics topics he obviously didn't understand himself, and so he himself would be in need of a refresher or two.

Since one has to start somewhere and this is ostensibly about physics (in reality it's about showcasing his own smartnessivity while consistently making errors indicating comprehension failures, so it's clickbait for an uninformed audience that wants to feel smart but isn't expected to be able to spot the problems in what poses as content there!--IOW a hipster circle-jerk in science-y sauce and now I'm proposing "jerkcircle" as group noun for hipsters), a link to something substantial dealing with physics, even very basic physics, would be the first choice. For let me be more clear than I ought need to be: It is about the lack of substance, not about the level. And in that case we go back to basics, revisit the foundations, make sure they're firm and well-understood, and build from there.

He is an "actual physicist".

[Anonymous Coward]

Not liking him doesn't remove his qualifications.

Your post demonstrates precisely why the question

[Anonymous Coward]

Your post demonstrates precisely why the question must be asked and answered. Rotating black holes have a toroidal shape (if they have a large enough spin). What about black hole capture of another black hole? Spherical? Not? When it's spiralling in, the shape changes.

Remember, the only shape we can see is the shape of the event horizon.

And it's not always spherical.

Your claim it is indicates why this discussion was entirely warranted. Even you, who believe yourself completely up to date and cognizant of the science have it completely wrong.

Slashdot error

[Anonymous Coward]

I keep going to slashdot and getting this weird site claiming to be news for nerds. I think the admin needs to add this to the .htaccess

Options +FollowSymLinks
RewriteEngine on
RewriteCond %{HTTP_HOST} ^slashdot.org[nc]
RewriteRule ^(.*)$ http://www.medium.com/$1 [r=301,nc]

Re:Yay meaningless prattle on unreadable hipster s

[Anonymous Coward]

Basic course is, I think, not something that one could expect to be interesting for a /.er

It's not the 90's anymore - the average /.er is a "geek culture" poser piece of crap.

Re:Yay meaningless prattle on unreadable hipster s

[Megol]

WTF is "geek culture"?

StartsWithABang - sod off!

[Anonymous Coward]

Earth calling StartsWithABang, come in StartsWithABang: Slashdot isn't your personal advertisement system for boosting viewership on your medium blog. How the hell do seemingly DOZENS of these fucking StartsWithABang stories make it to the front page of slashdot each month??? Fuck off. It's in no way shape or form NEWSWORTHY if a dude writes a speculative pop astronomy blog entry. Again. And again. And again.

And I love astronomy! I'm studied and well versed in the field and it's been a life long hobby. I read and watch TONS on the topic each month. When you piss off an astronomy lover like me, with astronomy, it should tell you something! SOD OFF.

Besides we have more important news - like how DICE HOLDINGS are a bunch of biased tyrants and practice censorship when their poop stinks on SOURCEFORGE.....

Or yeah. The other great one this week, "DUUUH, USB BATTUHRY, WHAT FOR CAN I USE IT FOR HUH? DUUUHHRRR... (BURP)"

And while i'm at it FUCK BETA. I protest, and am inches away from writing off this fucking website. It had a long and glorious history, but this shit that Slashdot has become is really depressing. I miss CmdrTaco....

Re:Yay meaningless prattle on unreadable hipster s

[Anonymous Coward]

Analytical event horizons of merging black holes

The Geometry of Black Hole singularities

Extremely poor article on black holes

[Antique Geekmeister]

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 velocity greater than C. Normal physics inside a black hole itself is critical to the "cyclic" models of the universe, where the gravitational mass is sufficient to draw the mass of the closed universe back and initiate a new "Big Bang". According to this model, the universe itself is one large black hole which we live inside. That's quite difficult if we're in a region of space that is "totally, utterly dominated by the force of gravity".

Some of the theoretical difficulty and potential for weird physics comes in observing the internal physics from outside the black hole. There's potential for a distinct set of physical laws, because it's effectively isolated and we can't observe the inside from the outside. But even those physical laws seem to obey angular momentum and charge, which can be be observed from outside the black hole itself much as the black hole's net gravity can be observed from outside.

Finally, there is no compelling reason to believe that there is _ever_ such an object as a completely spherical, detectable black hole, which is what this poorly researched article keeps talking about. Extremely small black holes, formed by possibly electrically neutral and non-spinning compressed objects, effectively evaporate extremely quickly for reasons described by Stephen Hawking described decades ago. Such an object might be spin neutral and electrically neutral, but would evaporate too quickly to be observed well at galactic distances. It's difficult to imagine there is any circumstance in which a larger black hole would have no spin whatsoever, and a spinning black hole is _not_ spherical. The earliest models of black holes described spinning black holes, including the work by Kerr, Penrose, and Hawking. (http://arxiv.org/abs/1306.1019)

It would be understandable to leave out such details in a shorter essay that didn't make such absolute claims. But no competent science editor would have ever let this be printed in any science magazine above the 1st grade level: the proliferation of bad chemistry, physics, and biology of such badly written content is a disheartening effect of modern web publishing.

Black Holes Have no Size

[Anonymous Coward]

Well, one might imagine a black hole would have a shape, since it is formed by gravity and thus the shape of the mass which is the source of the gravity would define the limits of the black hole. However, shape is information, and as we know, nothing can escape a black hole, and so information about the hole's shape cannot escape either. Indeed, the information that there is sufficient mass inside to generate a black hole cannot escape the black hole. The same goes for the information that the mass inside has become uncompacted in some sort of "big bang." We could be in a black hole right now, with our universe constantly expanding because our hole is constantly growing, yet we cannot escape our universe because all lines leading out of it simply curve back inside it, failing to connect to the space outside.

Damn, writing completely made-up BS is easy. I should have my own medium.com. I could call it psychic.com or maybe bullshit.com.

   

Some doubts

[Roger W Moore]

Asking questions like "Does a Black Hole have a shape?" makes you have doubts about those qualifications though. In physics you need to be careful to be precise. Anything which exists has a shape and yet he is not questioning the existence of Black Holes nor even whether they are spherical but rather whether they appear distorted from spherical by their gravitational field bending light.

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..

Re:Some doubts

[Roger W Moore]

It sounds like he was answering a different question: "What is the shape of a black hole?". That's a perfectly reasonable question to ask. Asking whether they have a shape is akin to asking: "Does something which exists have a shape?". In fact this article is actually a violation of Betteridge's law because the answer is 'yes', Black Holes do indeed have a shape although that answer imparts no useful information whatsoever.

Re: Some doubts

[Anonymous Coward]

"Anything which exists has a shape"

Again, you need to be careful here. This all depends on what you consider a "shape". Does "shape" mean a closed manifold? A shape as viewed from where? Since we know jack shit about black holes, most especially what lies beyond the event horizon, it's entirely possible that black holes don't truly have a closed manifold "shape"... Sure they might look like a circle or sphere from our perspective, but from inside the event horizon they might twist into any possible number of configurations that are not closed. If you ever hear anyone talk about the universe and they say "of course X is Y", you're dealing with a closed mind, and probably an imbecile.

Re:Yay meaningless prattle on unreadable hipster s

[Anonymous Coward]

Virginity, BO, bad teeth, personal grooming issues and horrendous fashion sense.

Yes

[Anonymous Coward]

It's basically a cone with a finite diameter but an infinite radius, if you consider the radius as the length of the side of the cone.

Shaped like ....

[PPH]

... medium.com. Because we just got sucked in again.

There goes the planet...

[__aaclcg7560]

I always though a black hole was shaped like a bathtub drain in space.

Re:Yay meaningless prattle on unreadable hipster s

[alex67500]

I thought that came along with being part of the Nerd Herd...

Does a black hole have a shape?

[Fuzi719]

Of course, and it looks like Kim Kardashian.

Better than more Rand Paul propaganda

[Anonymous Coward]

It's better than the Rand Paul propaganda that keeps getting posted.

The Republitarian whiners have managed to drive off nearly all the physics nerds--so this is what they get.

Re:Yay meaningless prattle on unreadable hipster s

[budgenator]

I think you have Nerd and Geek culture mixed up with plain Geeks.

You mean ...

[YoungManKlaus]

a shape other than round or elipsoid

Re:Yay meaningless prattle on unreadable hipster s

[lokedhs]

Her qualifications say: 'PhD in astrophysics, currently working at the University of Sussex". Say what you will about the content, but she does seem like a real astrophysicist.

Re:Yay meaningless prattle on unreadable hipster s

[tehcyder]

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.