General relativity tells us that very massive objects such as black holes warp space-time such that the path of any passing light is bent, an effect known as gravitational lensing. The theory also predicts that when a black hole rotates it will drag space-time around with it, creating a vortex that constrains all nearby objects, including photons, to follow that rotation.
Astronomers already have evidence that the supermassive black holes believed to lie at the core of many galaxies rotate. However, this evidence is indirect. The rotation of the Milky Ways black hole, for example, is suggested by the velocity distribution of stars within the galaxy, but this approach is undermined because we dont know exactly how much matter, particularly dark matter, the galaxy contains. Some astronomers believe that the Milky Ways black hole is rotating very quickly while others maintain it is rotating much more slowly.
In the latest work, Fabrizio Tamburini of the University of Padova in Italy and colleagues instead show how to detect the rotation by measuring changes to the light from a distant star or from the disk of accreted material surrounding a black hole. They point out that a wavefront travelling in a plane perpendicular to the black holes axis of spin will get twisted as it passes close to the black hole, since half of the wave front will be moving in the direction of advancing space-time and the other half in the direction of receding space-time. In other words, the phase of the radiation emanating from close to a rotating black hole should have a distinctive distribution in space.
The researchers used a computer simulation to model the phase distribution resulting from the rotation of the Milky Ways black hole and found that this variation ought to be visible from the ground. They say the way to measure it is to point an array of radio telescopes at the centre of the galaxy, using different telescopes to observe different segments of the approaching wave front, and then superimpose these segments to calculate their relative phase. This procedure would be repeated, each time the telescopes pointing to a different section of the tiny patch of sky surrounding the black hole.
Tamburini describes his groups findings as fundamentally important, given, he says, that most massive objects in the universe rotate. In particular, he believes that studying the rotation of black holes in active galactic nuclei can provide a lot of information about the evolution of these galaxies. And he maintains that his group could carry out such measurements within two years using an existing array of radio telescopes, such as the Very Long Baseline Array in the US, or the LOIS-LOFAR in Europe, were funding forthcoming.
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Astronomers calculate mass of largest black hole yet
PS3
AtomThick
Hey, don't get me wrong I can appreciate jokes ;) but what about holes made in water by a falling rock?
ubavontuba
And, it might imply a resistance to motion between mass and spacetime.
PS3
you could compare the effect maybe but I don't think so because the BH would be like never ending rocks from powerful gravity to pull in stuff which should degrade space like any other hole material.
Shootist
Frame dragging is a well recognized phenomenon. Spin a mass and it drags space-time along with it.
Everything has angular momentum. Find a black hole and you can be certain, it spins.
ubavontuba
Jaeherys
It has been shown that a supermassive black hole exists at the centre of our galaxy and many others. The orbital velocity of stars near the galactic centre require the mass of a black hole.
httpDELETE://en.wikipedia.org/wiki/Sagittarius_A*
Good image of orbits on this page, httpDELETE://www.astronomynotes.com/ismnotes/s9.htm
ennui27
Where does this rotation come from?
kaasinees
The rotation probably comes from its own force. Just like the stars dynamics comes from its own force.
ennui27
Note the 'non-rotating body' in the definition. Sorry, kaasinees ..I worded the question badly. (Did better the first time.)
Is this a developing truth? What was once believed is no longer valid>
AtomThick
It might spin but are some other examples that don't require spin to wrap stuff arround it: for example the drain of a sink it surely doesn't spin but the watter still gets the form of a vortex arround it.
soulman
Shootist said:
ubavontuba:
But you just said that you don't buy the whole frame-dragging hypothesis. Which is it? Do you accept that spacetime can be twisted by a rotating mass?
ubavontuba:
That makes no sense to me. Can you explain?
ubavontuba:
Why do you doubt that everything has angular momentum?
Jaeherys
Let's use the solar system as an example; imagine that the sun is invisible. Assuming we know the mass of the planets and their orbital velocities, you can determine the mass of this invisible sun using the equations on these pages,
httpDELETE://ceres.hsc.edu/homepages/classes/astronomy/spring99/Mathematics/sec10.html
httpDELETE://en.wikipedia.org/wiki/Elliptic_orbit
httpDELETE://en.wikipedia.org/wiki/Orbital_equation
Now back to the galactic centre, using the same equations and orbital velocities of the suns orbiting this "invisible" object, it is possible to determine the mass required to create (in this case) such high velocities.
Jake
Ethelred
This is similar to the physics joke that is so deeply based in a VERY standard joke that only the punch-line is needed.
First assume a spherical chicken of uniform density.
Ethelred
soulman
Sorry ubavontuba, I read your comment to read "I doubt that", instead of "I don't doubt that". Mea culpa.
Ethelred
There are NO black stars in the Universe because the universe isn't old enough. All stars are way above the background temperature of the Universe. No. Stars are held together by gravity. They cannot just 'shed' themselves. They can blow up. They can black hole. They can cease burning and form white dwarf. The blow up and form a neutron star then suck down matter from a companion star and THEN black hole after they consume enough mass.
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Ethelred
You know you could go look this stuff up. Kip's book is a bit old these days. And it doesn't say what you seem to think it does.
Ethelred
ennui27
Is that why every ....(repeat) EVERY definition of a black hole begins saying the mass of the singularity of a black hole is so strong that nothing ..... NOTHING can escape, even light.
Sometimes nothing means nothing and sometimes it means ...... I am not sure now?????
Jaeherys
httpDELETE://en.wikipedia.org/wiki/Hawking_radiation
wiki explains it better than I can.
Jake
kaasinees
It is already observed that black holes can leak radiation. It was observed by a blackhole eating a nearby star.
Jaeherys
That's just what daddy wanted to hear :D.
Snowboarder
First of all no black holes have been predicted to explode.... ever. The only way for a black hole to "die" is through the process of evaporation postulated by Hawking. There are absolutely no other viable theories for how a black hole can lose mass/energy.
Hawking radiation works as follows. Two imaginary particles come into existence near the event horizon of a black hole, one normal particle, one anti-particle. Normally they destroy each other. But near a black hole two things can happen. If the normal particle is sucked in the anti-particle follows. No net gain/loss. If the anti-particle is sucked in it destroys a particle already in the black hole and the normal particle is shot out as Hawking radiation. The result is a loss of mass for the black hole. This is the only way for a black hole to lose mass.
ubavontuba
Snowboarder
Any black hole near even a small amount of matter will gain more mass than it loses through Hawking radiation. Even if it wasn't gaining mass, any black hole of a respectable size would take far longer than the 13.7 billion years the Universe has been in existence to evaporate.
You keep referring to black holes as dead stars that have burnt out as if they are simply stellar light bulbs that no longer function. It is vastly more complicated than that. When a star runs out of fuel it doesn't just burn out. The energy from fusion becomes no longer sufficient to stave off the effects of gravity and it collapses into a singularity. A singularity is not a burnt out light bulb, it is a collection of matter so dense that even the equations of relativity break down within it. A singularity does not behave in any way like a star.
You should either read more about the nature of black holes... or read more carefully :)
soulman
Only from an external reference frame. If you were near a BH, your personal clock would tick away just as usual.
This is a consequence of different frames of reference and has nothing to do with BHs, per se.
Time flows at a different rate on the surface of the Earth compared to, say LEO, with countless transitions in between. But, if you measure time on Earth it will flow at 1sec/sec and it will likewise aboard the ISS. It's only when you compare the two clocks in the same frame of reference that you will see a difference.
How does it follow that clocks can go backwards?
soulman
Because he badly mangled the mechanism of Hawking radiation production. In hindsight, I should have rated him higher because he was spot on in the first part of the post (not dealing with HR).
Ethelred
That is NOT Hawking radiation. That is radiation from an accretion disk and the very first black hole candidate, Cygnus X-1, was found from the X-ray radiation generated by the accretion disk.
Ethelred
Ethelred
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Ethelred
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Ethelred
Your misunderstanding of black holes is quite clear. They are no longer stars.
I see. You want to suppress dissent.
Ethelred
Ethelred
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Ethelred
If you want to be understood you really need to write with one hell of lot more clarity and frankly your use of the term 'black star' makes it hard for anyone to think you don't mean a black star instead of a black hole. Non-standard SECRET definitions is a sure way to be thought a Crank.
So how about you clarify your position using standard terms instead of special definitions that only make a mess of things?
Ethelred
omatumr
arxiv.org/pdf/1102.1499v1
Cosmologists have become as dogmatic and irrational in the 20th and 21st Century as the Religionists were in the 16th and 17th Century. E.g.,
youtube.com/watch?v=AQZe_Qk-q7M
With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo
Ethelred
This has been pointed out to you before by others and you just plain pretended it never happened. This is typical Crank behavior and just one more of many that show that your simply aren't interested in testing your hypothesis.
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Ethelred
Go run the bloody numbers Oliver. See how a large a mass of neutrons can become before you get a black hole. Go read the results from the iron stacks while you are at it and notice the total lack of neutron decay. You don't have anything else to do so what if it takes you several months to work out the numbers. If you find you are right then its a good thing and if you find out that you are wrong you can stop wasting time and stop looking like the Arps do.
Heck you could even admit you are wrong and that woud be such a rare thing that it might go a long way to repair your reputation. You produced real evidence that a supernova was closely involved in the creation of this solar system. That is something real as opposed your idea that OUR sun was the supernova which is contrary to evidence.
Ethelred
omatumr
Dogmatic religionists and dogmatic scientists are identical twins hiding under different cloaks of respectability.
That is the central lesson here:
youtube.com/watch?v=AQZe_Qk-q7M
and here: arxiv.org/pdf/1102.1499v1
ubavontuba
The article refers to two frames of reference. One, observing the other from a distance. Relevant to the article, it's the observer's frame of reference which I'm discussing. It doesn't, which as I indicated with my causality remark, is why this experiment won't work.
continued...
ubavontuba
It can be said that a black hole has angular momentum, but relative to a distant observer, is it rotating in real time?
What happens to backlight that passes very close to an intervening black hole's horizon? Will our distant observer see it?
soulman
That's the kind of guy I am.
Except that your causality remark didn't make much sense, and is why I asked for clarification.
What's 'real time'?
What's 'backlight'?
Please do, it might make more sense then your ambiguous questions and nebulous terminology.
Ethelred
George Wallace changed and became a decent human being. So can you.
And the covers you on two counts as you are going on YOUR own dogma over actual evidence.
Run the bloody numbers. That is what REAL scientists do.
Ethelred
Ethelred
This white dwarf is a candidate for the oldest white dwarf and it is still 3800K or 1000k hotter than a standard tungsten light.
httpDELETE://arxiv.org/abs/0804.1570
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Ethelred
httpDELETE://www.astronomy.ohio-state.edu/~ryden/ast162_4/notes17.html
There NO black dwarfs yet in the universe and that means there are no black stars.
There is no such thing. And you did NOT read about such a thing in Kip's book. Black holes come from stars that are not in the least black. Red Giants are not black.
He did no such thing. It just emits energy at a higher and higher rate till there is nothing left. That is not an explosion.
That book and many more. You do know that there are OTHER books don't you?
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Ethelred
There are NO black stars in our universe. We do have white dwarfs AND if FIVE white dwarfs were to conjoin without a mass loss in the process they would become a black hole. BUT no one has suggested that such a thing has occurred. Black holes could come from some supernova events but those suns that do that were NOT black. Mostly they are expected to come from Red Giants though Supernova 1987A seems to have been a Blue Giant before it went Supernova and it may have formed a black hole as there is no present sign of a pulsar.
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Ethelred
Reasonable criticism, like mine was, is NOT a smear. You were so busy turning a suggestion for more clarity into a nonexistent smear that you just plain ignored my pointing out to you that there are no black suns because no sun has ever gotten cold enough to be black. Nor has any black hole evaporated, unless there are quantum black holes, since the Universe is WAY too young. At present any stellar mass black hole is GAINING mass because the background temperature of the universe is higher than the temperature of any such black hole.
Ethelred
omatumr
"Dogmatic religionists and dogmatic scientists are identical twins hiding under different cloaks of respectability."
With kind regards,
Oliver K. Manuel
ubavontuba
Do you actually understand the article?
Heck, you could've at least looked up the definitions, yourself. That you didn't bother to do so casts an unfavorable light on your ability to understand and process information.
soulman
Yeah, that must be it.
Still waiting for the spilling of beans. I bet it won't amount to a hill.
Ethelred
It is YOU that is being dogmatic.
It is YOU that refuses to look at evidence.
It is YOU that refuses to run the numbers that you should.
And it is you that backed a plasma universe post that totally disagrees with your own ideas and they did run the numbers. Got numbers that don't work so they try to pretend it never happened instead of dropping their incorrect theory. Might by why YOU refuse to run the numbers or look at the total lack of evidence for decay of bound neutrons.
And in this case you are backing person that not only thinks there are black holes which you claim exist he thinks there are black suns which really don't exist.
Ethelred
ubavontuba
Do you understand why backlighting is important in this case, yet? I notice you didn't answer the question: Do you actually understand the article?
So, do you?
Snowboarder
@soulman
Thought I had a decent understanding of HR in layman's terms. Can you explain/point the way to an explanation that is correct.
@Ethelred
Thanks for being the voice of reason. I have no experience/schooling in math/physics/science and I read this site in my spare time to try and be as knowledgeable as possible on these subjects I find so fascinating. Misinformation is frustrating.
Quantum_Conundrum
However this will be limited by the effects of relativity, if relativity is even true, and if the laws of relativity don't break down inside event horizons.
The consequences of this is that all accretion-formed singularities rotate at infinitesmally close to the speed of light due to conservation of angular momentum.
They could only avoid doing so if they were at absolute zero, which nothing is at absolute zero.
Think of it this way. Light itself supposedly cannot escape the event horizon. But the "singularity" inside is smaller than the event horizon, and so it must be rotating equal or faster than the event horizon rotates.
Quantum_Conundrum
The probability of this ever happening is virtually non-existent.
Due to conservation of angular momentum, if a collapsing star has any spin whatsoever, then the resulting black hole will eventually spin faster and faster as the singularity collapses, and will always get closer and closer to the speed of light as the "radius" decreases to zero.
Quantum_Conundrum
This is the same reason ice skaters spin faster by pulling in their arms.
nxtr
ShelMar
Nobody misunderstood what stars was saying, it was understood exactly as written.
Lets disprove his nonexistent "smear campaign" theory...
@71STARS(1st post)
Feb 14, 2011
Black holes are not 'holes' but simply black, dead stars. The person that made dead holes come to life with gravitational pull has created the biggest fantasy of our age. Picture a star dying, out of fuel, going black. That is a what is mis-called a Black Hole.
71STARS - Feb 15, 2011
@Ethelred:
Your separation of dead black stars (because they no longer emit light) from the stage of black holes is either shocking or quite sad. No reply.
cont...
ShelMar
Rank: 1.8 / 5 (8)
One final word. My simple terminology has been smeared by someone named Ethelred. Please know:
Black Star: a dead/dying star that no longer emits LIGHT is my terminology. Color: black. Not to be confused with "black hole."
Black Hole: the hypothetical RESULT of a dead STAR which implodes. Not to be confused with the initial dark, invisible, dying star which causes the result.
I believe that should clear up any of my words that have been twisted. It's a shame to distort what a person says.
Stars, apparently its your separation of dead black stars and black holes that is shocking or quite sad.
That should clear up any claim his words have been twisted. It's a shame to falsely claim a person distorted what you said.
Disagree;You can't. Misstate;You did. No reply.
Skeptic_Heretic
There is no known mechanism by which matter can have a temperature of absolute zero. We haven't been able to do it in the lab, we haven't seen observational evidence for it, space time itself is of a higher energy than absolute zero.
In short, you're full of shit.
Skeptic_Heretic
Ethelred
However if light is being pulled down then it IS a black hole and no longer a star. That is a black hole and not a star. It separated from the rest of the Universe by the Event Horizon. You separation is a fantasy because NO STAR IS BLACK. NONE. They ALL glow. EVERY ONE OF THEM. What is so difficult for you to understand about this?
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Ethelred
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Ethelred
Tungsten-halogen bulbs are only 3200K. At 5000K all the elements are a gas.
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Ethelred
So to reiterate.
There are no black stars in this Universe. They all glow.
If a ex-star has such an intense gravity field that it sucks down light it is a Black Hole and no longer a star.
I never claimed to be an authority. It is Oliver that is claiming to be an authority that should not be questioned.
I have actual evidence on my side. Where is yours for the existence of black suns as opposed to black holes, white dwarfs and neutron stars. Please post a link to something that shows or at least implies their existence as that is our main, though not only, area of disagreement.
Ethelred
Skeptic_Heretic
Ethelred
Ethelred
lomed
Snowboarder
@frajo
I'm an absolute layman, and you're correct.
Somewhat off-topic question...
Can a sufficiently dense and massive amount of dark matter form a black hole?
lomed
Skeptic_Heretic
Skeptic_Heretic
There's the literature and definition of a black dwarf.
Go ahead and further continue to admit that you are wrong, and using incorrect terminology.
Ethelred
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Ethelred
Either way, red giant or straight to a bang, stars don't go through a black stage before a supernova. You had the truth from us already and you could have looked it up on dozens if not hundreds of sites on the web. Can in theory. None are yet black or even at red heat. EVENTUALLY. None yet in the entire universe unless it is MUCH older than it appears to be.
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Ethelred
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Ethelred
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Ethelred
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Ethelred
ttp://www.eg.bucknell.edu/physics/astronomy/as102-spr00/web_pages/web8.html
ttp://en.wikipedia.org/wiki/White_dwarf See. No black stars. Not yet.
Use the WEB Luke. It can inform you and keep you from ignorance.
It is also full of Cranks so use critical reasoning and multiple sources.
Ethelred