Black Hole's "Point of No Return" Found 130
dsinc writes "Using a continent-spanning telescope, an international team of astronomers has peered to the edge of a black hole at the center of a distant galaxy. For the first time, they have measured the black hole's 'point of no return' — the closest distance that matter can approach before being irretrievably pulled into the black hole. According to Einstein's theory of general relativity, a black hole's mass and spin determine how close material can orbit before becoming unstable and falling in toward the event horizon. The team was able to measure this innermost stable orbit and found that it's only 5.5 times the size of the black hole's event horizon. This size suggests that the accretion disk is spinning in the same direction as the black hole. The observations were made by linking together radio telescopes in Hawaii, Arizona, and California to create a virtual telescope called the Event Horizon Telescope, or EHT. The EHT is capable of seeing details 2,000 times finer than the Hubble Space Telescope."
Editors (Score:5, Informative)
What in the name of everything you hold holy were you thinking when posting this?
Sure, the news is interesting, but while we're getting used to spelling errors and broken links on the front page, a blatantly mis-formatted link is something new, I think.
Re:Editors (Score:5, Funny)
What in the name of everything you hold holy were you thinking when posting this?
This is Slashdot. They hold plaintext holy.
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Sure, the news is interesting, but while we're getting used to spelling errors and broken links on the front page, a blatantly mis-formatted link is something new, I think.
Not in a Slashdot summary... The "editors" post them fairly regularly.
Re:Editors (Score:5, Funny)
What in the name of everything you hold holy were you thinking when posting this?
I think you meant to say:
What in 'http://news.harvard.edu/gazette/story/2012/10/the-name-of-everything-you-hold-holy-were-you-thinking/the name of everything you hold holy' were you thinking when posting this?
Re:Editors (Score:4, Insightful)
I think at this point in time, you could probably randomly assign slashdot editorship to anyone with an internet connection and get a more dedicated, professional, giving-even-the-slightest-shit approach to the task.
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you could probably randomly assign slashdot editorship to anyone with an internet connection
That's smart. Open the doors to those with good comment karma and then track their editor karma separately. Lord knows, there's no lack of willingness to provide feedback on editorial quality here.
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That's even better! And actually practical.
Readers definitely seem to have a greater investment in the quality of the site than the editors do.
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I was thinking the black hole sucked the HTML tags out of the original post.
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Very appealing to the mainstream, i guess, but i wonder why go ahead and say "Black Hole"? Sounds fairly boring. Better call it "Giant Sucker" or so next time.
Re:Editors (Score:5, Informative)
Of all of the things the editor got wrong on this post, this is one of the things actually stated in the stub. I can forgive you for not getting that far, though; This post is utterly appalling.
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Glad my post got still modded up tho
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It is one thing to not RTFA, but couldn't you at least read the summary? They are not talking about the event horizon smarmy-pants.
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I need a plugin (Score:2)
That link cleaned up (Score:5, Informative)
If you're too lazy to cut and paste. :)
http://news.harvard.edu/gazette/story/2012/10/point-of-no-return-found/ [harvard.edu]
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Re:That link cleaned up (Score:5, Interesting)
Thanks for that. Not everyone can view /. via a home computer screen with mouse. I was going to try to meticulously "select text" myself on my 2 1/2" smartphone screen and post the link, an excercise in futility at times.
First world problems.
Besides not being funny any more, your statement demonstrates a lack of knowledge of mobile devices in developing countries.
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Yeah I bet non clickable links are a major problem when you're forced to work as a slave labourer underground for Kali cultists until their high priest tears your heart out in a savage ceremony.
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Not everybody in the "third world" lives like that.
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Not everybody in the "third world" lives like that.
You are missing the Temple of Doom reference.
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Or, you know, if you use Firefox you can select the link and right click...
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Did you use CTRL-X or CTRL-C? Or Edit/Copy vs. Edit/Cut?
I'm guessing it was copy. Copy and paste. Like Xerox, a copier. Not a cutter.
"Cut and paste job" refers to the older method of physically cutting apart something to make a new work. Like Thomas Jefferson's Bible. It is also pejorative, implying something that can be done by one with little brain.
You can say the piss poor editing is a "cut and paste" job, because it is. A user being too lazy to "copy and paste" is pejorative enough, going the ext
Unstable? (Score:1)
What does unstable mean? I hadn't thought an orbit can be unstable outside of sf-movies ;-). How does an atom in orbit loose energy to fall into the black hole? Gravitational or electromagnetic waves?
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Re:Unstable? (Score:5, Funny)
Anyone versed in GTR here to help?
When the heart rules the mind
One look and love is blind
When you want the dream to last
Take a chance forget the past
Seasons will change
You must move on
Follow your dream
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Anyone versed in GTR here to help?
When the heart rules the mind ...
Yes, a perfect example of why we came up with the "Blah blah blah (Bbb)" construct, so no-one would go tripping off to "Grand Trunk Railroad" when "General Theory of Relativity" was intended. :-P
Sigh. Maybe the "editors" should outsource editing to /. readers. Email the submission to five /. readers you trust, tell 'em to review it and write a summary, then the "editor" picks one of the submissions which will be the summary/submission.
"Editor" problem solved. You're welcome. I guess I should patent it n
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Anyone versed in GTR here to help?
When the heart rules the mind
One look and love is blind
When you want the dream to last
Take a chance forget the past
Seasons will change
You must move on
Follow your dream
Burma Shave.
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What does unstable mean?
Could be many things... gravitational tidal stresses exceed any known material tensile strength, maybe the Unruh effect if it really exists exceeds the vaporization temperature of everything, maybe hawking radiation vaporizes any known thing... Which one wins probably depends on total mass...
A journalist filter is like an event horizon, in that information cannot escape once it enters. Which is too bad.
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gravitational tidal stresses exceed any known material tensile strength
Tital stress for a free falling object is finite at the event horizon. The more massive a black hole is the lower the differential gravity at the horizon.
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Indeed, I doubt a human in free-fall would feel a thing when crossing the event horizon of a supermassive black hole, it's the little ones you have to watch out for.
Well, yes, that too. The bigger reason a human would never feel a thing when crossing the event horizon is that the neurons in his brain that were closer to the black hole would be unable to send signals to the neurons further away.
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Depends on the size of the hole. There does not have to be a large gravitational gradient at the event horizon.
Black holes don't create gravity.
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I researched it some more and
http://en.wikipedia.org/wiki/Epicyclic_frequency [wikipedia.org]
seems to explain it.
Maybe a really poor /. car analogy is that some cars, when you try to skid pad test them to see what kind of cornering force you can muster, will smoothly take on load and spin faster and smaller circles, but at a certain radius they just fling out of control all over the place all random like, and it turns out fluid/vapor orbiting a black hole behaves the same way, smoothing spinning in until at a certain defin
Re:Unstable? (Score:4, Informative)
I regard this as basically a red herring, not to mention mixing up two different things.
The epicyclic frequency and disk stability has to do with the fluid dynamics of an accretion disk - that kind of stability does not require a black hole (look at Saturn's rings, which also have sharp edges).
The key word in Innermost Stable Circular Orbit is "stable" - the meaning is not that this orbit is not decaying (it is), but that it is stable to small perturbations. Inside the ISCO, a small perturbation will cause big changes, and the orbit will rapidly decay. So, outside the ISCO, the orbit is slowly decaying - "inspiraling" - while inside the ISCO, the orbit will decay very rapidly (i.e., "plunge" into the black hole). But, still, if you had a super-duper rocket, you could escape to infinity from inside the ISCO, as long as you hadn't crossed the event horizon.
All of this ignores tidal deformations, which convert orbital energy into heat and can also rapidly decay orbits.
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>look at Saturn's rings, which also have sharp edges
I believe the sharp edges of Saturn's rings are attributable to the shepherd moons. This also appears to be true for the rings of Jupiter and Uranus. Not enough is known about the Nuptunian ring system to say for certain about it.
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A journalist filter is like an event horizon, in that information cannot escape once it enters. Which is too bad.
At last; media explained.
Re:Unstable? (Score:4, Informative)
In Newtonian gravity, 2-body orbits are stable, unless there is drag or some other non-gravitational force.
In General Relativity, orbiting bodies emit gravitational radiation, which carries away orbital energy, and so no orbit is truly stable. However, this only really becomes important near a neutron star or (even more so) near a black hole, where the gravitational radiation energy loss can be significant, and objects can spiral into each other fairly rapidly.
Of course, in either theory, the question of the stability of 3 or more body orbits is very complicated, and still an open area of research, but suffice it to say that N >2 body orbits need not be stable, although ejection of orbiting material is more likely than capture by the central body.
Re:Unstable? (Score:5, Interesting)
Comment posting limits (and time...) won't let me respond to many individual comments, so I will see if I can address a few things at the same time here.
For a given angular momentum of something going around a black hole, you can work out what potential energy it would have at different radii. In a normal Newtonian case, you can think of having some satellite orbiting at some speed. If you try to push that satellite further in, while still maintaining its angular speed, it will try to pop back out since it is essentially going too fast to orbit at a smaller radius. There is a minimum in the potential energy of the satellite where it would have a circular orbit for that given angular momentum, as it would just stay at that radius. The potential energy about this radius would be like a bowl, if you push the satellite inward, it would roll back down toward the radius corresponding to a circular orbit. Momentum would of course carry it beyond that point, so it would oscillate in radius between some place closer and some place further from the circular orbit. This would give you an elliptical orbit where the radius goes between two values. The potential energy for over radius for a given angular momentum would look roughly like the red curve in the image here [oregonstate.edu].
Now, for a black hole, GR gives some differences from Newtonian gravity when you get closer. The potential energy curve now looks more like this [amazonaws.com]. There is still a stable orbit, as you can see it could oscillate around the minimum there like a marble in a bowl. In other words, small pushes on a perfectly circular orbit will turn it into a slightly elliptical orbit that is still pretty close to the circular one. However, if you push it far enough inward to get over that bump, the orbital radius would be like a marble just rolling down that hill toward the black hole. Now, the size of that bump changes depending on what angular momentum you are talking about. As you increase the angular momentum, which in Newtonian gravity would just give you a smaller radius for a circular orbit, that bump gets smaller. There is a point where the bump goes away, such that you just now have a curve that decreases with decreasing radius. Hence, a particle in such an orbit would continue to move closer to the black hole, as there is lower potential energy the closer it gets.
This is all due to the geometry of space around a black hole. Weird stuff like the circumference of a circle not being 2 pi r depending on how you measure the r from the black hole, which is why orbits no longer have the same stability they have in Newtonian gravity. This is not an effect due to gravitational waves. The orbiting particle can be something like a proton where the gravitational waves would be too small to matter. However, if you are talking about the orbit of a massive object, like a star or second black hole, then the gravitational waves become significant. In that case, the orbit at any radius would slowly decay due to emitting gravitational waves. Once the decay orbit hits the radius of the innermost stable orbit, the decay would greatly accelerate.
This is also not an effect of rotation or frame dragging, as it happens with a non-spinning black hole solution too. However, spinning black holes and frame dragging do factor into it, such that for a spinning black hole, the inner most stable orbit is smaller if you are going in the right direction around the black hole. Although there are other effects that the frame dragging causes. You get things like the ergosphere, a region where due to frame dragging, you would have to go faster than light to look stationary from an outside viewer, so all matter within that region is spinning around the black hole.
This is also quite distinct from the event horizo
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Even without coffee this was a really insightful explanation. I would have to go back to university to study GR to grasp the influence of this geometry of space but the graphs provoke a dim understanding of the unstableness (is this a word?) of an orbit. thanks.
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This is also quite distinct from the event horizo
For an instant, before I saw "Read the rest of this comment...", I thought, OMG, the post got sucked in!
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How does an atom in orbit loose energy
Fission and fusion usually set LOTS of energy free.
I thought they were both the same. (Score:4, Insightful)
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The Event Horizon concerns massless particles (e.g. light) , the Stable Orbit massive.
Re:I thought they were both the same. (Score:5, Informative)
Nonsense. Light can fall into a stable orbit too! And light, because it's moving, has mass too.
Maybe you meant matter, when talking about the stable orbit.
Ugh. No. Photons have no mass. They have momentum. Relativistic mass isn't actually mass, and in fact, physicists have been trying to get rid of the term, because of the confusion it causes.
Point of no return = distance below which no stable orbit can exist. If you have thrust, you can actually get out of the "point of no return", it's further away than the event horizon. You just can't have an unpowered orbit that won't eventually decay into the event horizon.
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Imagine a 1 kg beachball made out of highly reflective material. Now add 1 kg*c^2 joules of photons bouncing inside it. Will the gravitational attraction of the object you created be that of 1 kg or 2 kg?
"Mom! My beachball just exploded and vaporized the dog!"
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2 kg. However, it is more useful to think of this as the sum of the mass of the beachball and the energy of the photons because both of these can be measured in the rest frame of the beach ball. In the rest frame of a photon, the photon doesn't exist. This is another way of saying that photons do not have a rest frame and that they do not have mass. It is clearer to equate rest mass with mass to keep it separate from measurements different observers will disagree on. All observers will agree on the rest mas
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I've never looked at the wikipedia articles you mention except to look up the mass of the proton.
In my opinion, the invariant mass-energy of a system should just be called mass. For fundamental particles with no internal structure (as far as we know) like electrons and quarks, this would be the rest mass. By this definition, photons have no mass because they have no invariant mass. For a compound system, like the proton, the invariant mass is its total rest frame energy divided by c^2. The total rest fr
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Yes, I said as much in my second to last post.
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I've worked with many physicists, some who agree with you, some with me. As long as the math works out, either way works.
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Gravity doesn't act on mass directly. A black hole (or any other large mass) warps the space around it. Light travels in a straight line through curved space (a geodesic if you want to be technical about it). It's similar to how, if you walk in a straight line on Earth, you actually walk in a circle due to the Earth being round.
Re:I thought they were both the same. (Score:5, Informative)
as i understand it, the Event Horizon is the singularity limit from which light cannot escape. the Innermost Stable Orbit is the closest distance a physical object in space can orbit the black hole without being sucked into it.
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Orbits outside the ISCO are slowly inspiraling into the black hole, under the effects of gravitational radiation (and in the real world also other things, like tidal deformations and accretion disk drag.)
Inside the ISCO, the orbit becomes unstable to perturbations and there is a "plunge" into the black hole. However, these objects are visible to the outside as long as they haven't crossed the event horizon. The thing is, that won't take long, and so they won't be visible for long.
For more details, see this
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A lot. If you had a super-duper rocket, and were orbiting at the innermost stable orbit, you could escape the black hole. If you went through the event horizon, you could not.
Re:I thought they were both the same. (Score:5, Interesting)
The event horizon and the innermost stable orbit have a band of space between them. What happens if you go there?
First, these regions near a black hole tend to be very nasty for our kind of life. Lot's of radiation, and the tidal stresses will kill you for a solar mass black hole. So, suppose you have a multi-billion solar mass black hole to play with, lots of shielding, and a super rocket as well. The ISCO orbit will be about 2 days in that case.
Could you make a regular orbit inside the ISCO? Yes, in principle, down to the Innermost _Unstable_ circular orbit, AKA the "photon orbit," as this is (at 1.5 Schwarzchild radii) where photons would orbit. It's unstable, so you will need to maneuver frequently to not fall into the black hole.
Below the IUCO, you have to fire your rockets constantly to avoid being sucked in. Better not run out of fuel !
A movie is worth a lot of words, so here are some movies of orbiting a back hole ISCO [colorado.edu].
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here are some movies of orbiting a back hole.
I've been on the Internet long enough to know not to click THAT link.
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I'd like someone to explain to me why my pet theory is "not even wrong".
The theory goes something like this: as something falls below the Event Horizon, the gravity slows time down until it stops, meaning the thing never reaches the centre, so the singularity is never actually reached. Hence black holes have varying sizes & masses and aren't simply a point with an EH around it.
After all, if the singularity were true, wouldn't all black holes be merely a singularity with an EH?
Can you briefly explain ho
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The difference is, you get flushed down the drain,instead of just circling the bowl.
But at least with a black hole, you don't have to dodge the floaters, and never need a plunger or plumber! ;-)
An obvious point, but... (Score:1)
Black holes are neat.
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It this a known fact, or speculation?
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We know that they exist, and now it seems that we know that they rotate. (Ok, "know" may be too strong a word, we have empiric confirmation of both. With some certainty that is smaller than 1, of corse.) My question was if we have any empiric confirmation that black holes have hair.
I asked it because last time I saw anything about it, there were only speculation either way.
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FTA; “Once objects fall through the event horizon, they’re lost forever,”.. You walk through that door, you’re not coming back.”
*** Yeah, I almost got married once, too. ***
That would actually be a wormhole. You can come back again "on the other side", in another universe, i.e. less the house and plus the alimony payments...if you were the husband of course.
Black Hole's... (Score:2)
A black hole's 'http://news.harvard.edu/gazette/story/2012/10/point-of-no-return-found/point of no return'? I know a little bit about GR but I don't think I've every heard of that physical quantity before. Is this some new "mystery" technology like quantum computers, some sort of Swarzschild Uniform Resource Locators?
Starship fate (Score:2)
Re:Starship fate (Score:5, Funny)
Imagine you are on a starship and have to pass near a black hole.
You read up the facts from the books and set your course.
5.5 times the size of the black hole's event horizon seems rather risky.
I would take 3 times the suggested distance to pass safely.
I'll keep that in mind next time I pilot my starship past one.
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Have you noticed how your peers cringe whenever you try to tell a joke? Trust us, you don't need to *duck* because we feel you are more to be pitied than censured.
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Have you noticed how your peers cringe whenever you try to tell a joke? Trust us, you don't need to *duck* because we feel you are more to be pitied than censured.
That, and this is /.; we're geeks not "pro-sports guys"
Even if we tried throwing things at him, we'd miss... he's better off standing where he is, instead of moving (and then potentially getting hit by a stray shot)
Accretion disk spinning the same way? (Score:2)
How is it possibly surprising that the accretion disk is spinning the same way as the black hole itself? The same stellar evolutionary forces that created the galaxy and imparted spin to it would impart mostly consistent spins to every star and to the core structure of the black hole, built out of the same intragalactic nebulae. Is there any process that could impart a different spin to the accretion disk than to the core black hole itself?
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I don't know the mechanism that forms them but black holes that spin opposite to their accretion disks are called retrograde [wikipedia.org].
inaccurate summary (Score:5, Informative)
The harvard.edu news article, quoted in the slashdot summary is inaccurate. It says:
This reads as a claim that they've resolved the event horizon. That's not true, although there are good prospects for resolving the event horizon of a black hole in the near future.
As is made clear in the rest of the article, and in the abstract [sciencemag.org] of the published paper, what they've really resolved is structure inside the innermost stable circular orbit (ISCO) [lsu.edu].
In units where G=1 and c=1, the radius of the event horizon is 2M, where M is the mass of the black hole. The radius of the ISCO, for a nonrotating black hole, is 6M, i.e., three times the radius of the event horizon. What they've resolved is structure at 5.5M.
The first author of the paper, Doeleman, seems to post all his papers on arxiv.org, but unfortunately this one doesn't seem to be there yet, and Science has their copy paywalled.
If U gaze long into an abyss,it gazes back upon U! (Score:2)
(Friedrich Nietzsche)
Re:If U gaze long into an abyss,it gazes back upon (Score:4, Funny)
What does it take to be a Slashdot editor? (Score:3)
Powered slingshot around a black hole? (Score:1)
IANAP but would a a powered slingshot (https://en.wikipedia.org/wiki/Gravitational_slingshot#Powered_slingshots) through the zone between the Event Horizon and the Point Of No Return of a Black Hole could theoretically facilitate achieving enormous speeds enabling fast deep space travel? Or would you have to do it outside of the Point Of No Return?
The EHT (Score:1)
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The incoming mass has inertia, which will spin up the black hole as its pulled in.
There appear to be two huge forces at work... gravitational, electric forces, and centrifugal force. One is trying to hold everything together, the other is trying to blow it apart.
Its a pet theory of mine that what we know as the "big bang" is actually the result of a massive black hole
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Angular momentum (rotational energy if you like) causes frame dragging (http://en.wikipedia.org/wiki/Frame-dragging), which produces orbital precession. A massive rotating body also induces AM in smaller objects orbiting it. Objects orbiting in the same direction as the main body rotates have higher inertia (greater rest mass) and they in turn influence other objects more strongly. Objects orbiting with the AM tend to clump up more than those orbiting against the AM. Time dilation is affected by whether