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Spinning Black Hole's Edge Rotates At Nearly the Speed of Light
astroengine writes "Astronomers have directly measured the spin of a black hole for the first time by detecting the mind-bending relativistic effects that warp space-time at the very edge of its event horizon. By monitoring X-ray emissions from iron ions (iron atoms with some electrons missing) trapped in the black hole's accretion disk, the rapidly-rotating inner edge of the disk of hot material has provided direct information about how fast the black hole is spinning. Astronomers used NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) — that was launched into Earth orbit in June 2012 — and the European observatory XMM-Newton measured X-ray radiation as a tool to directly infer the spin of NGC 1365's black hole. 'What excites me is the fact that we are able to do this for the very massive black holes at the centers of galaxies but we can also make the same measurement for black holes in our galaxy ... black holes that resulted from the explosion of a star ... The fact we can extend this from billions of solar masses to 10 solar masses is pretty cool,' Fiona Harrison, professor of physics and astronomy at the California Institute of Technology, Pasadena, Calif., and principal investigator of the NuSTAR mission, told Discovery News."
i love how this summary explains what an ion is, but assumes i know the definitions of black hole, x-ray, and solar mass. great writing, folks!
Have they shown that the black hole is rotating near c, or just that the accretion disk is rotating near c at the event horizon? The accretion disk and the black hole are not necessarily spinning in sync. If they mean the accretion disk, then, like DUH: if it wasn't rotating near c, it would fall straight in and there wouldn't be a disk.
You might as well say it's because they are made of rainbows and ponies unless you have math to support your theory.
They are obviously made of strawberries and unicorns.
"Lack of speed can be overcome. In the worst case by patience." --Znork
I had a Honda Civic that could go the speed of light. It sucked because nothing ever showed up in the rear view mirror.
Let's make like a bird... and get the flock outta here.
http://helios.gsfc.nasa.gov/qa_sp_gr.html
" Yes, light is affected by gravity, but not in its speed. General Relativity (our best guess as to how the Universe works) gives two effects of gravity on light. It can bend light (which includes effects such as gravitational lensing), and it can change the energy of light. But it changes the energy by shifting the frequency of the light (gravitational redshift) not by changing light speed. Gravity bends light by warping space so that what the light beam sees as "straight" is not straight to an outside observer. The speed of light is still constant."
Dr. Eric Christian
In my limited understanding of these things, (mostly from articles meant for mass consumption, not scholarly journal papers), I imagine a black hole to be so massive not even light can escape its gravitational pull. Which technically means the escape velocity is the speed of light. So anything at the event horizon should be at the speed of light. This is of course, a naive view. The escape velocity is based on Newtonian, not Relativistic, physics.
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
So many people (a number of whom who should know better) get this totally wrong because you always here that a black hole has "such powerful gravity that not even light can escape!!!111!!!"
This is another failing of Science Channel styled science shows*. They neglect to tell you that light doesn't escape because the gravity well created by a black hole warps space, not because photons are pulled on by gravity. It may sound like I'm splitting hairs since the overall end result is the same but a lot of people mistake it as meaning that light is sucked in to the black hole because particles with mass are also sucked in. This also doubtlessly leaves people scratching their head over the misconception that maybe the gravity is forceful enough to actually attact the light.
* Yeah, I'm the guy who complained about definitions being used too often in another thread.
No. Black holes are not dark matter. Well, I mean, yeah, they are dark. Like black dark. Like "how much more dark could they be? None, none more dark." But they are normal matter, not dark matter. The mass of (nearby) galactic core black holes is easily measured by measuring the speed of closely orbiting stars. Their velocity is entirely dependent on the mass inside their orbit, so no need to invoke dark matter.
c is a constant represents the theoretical maximum speed of light. The problem is that the speed of light is not constant. Light slows down in a medium.
Learn to love Alaska
do black holes blend?
It may sound like I'm splitting hairs since the overall end result is the same but a lot of people mistake it as meaning that light is sucked in to the black hole because particles with mass are also sucked in. This also doubtlessly leaves people scratching their head over the misconception that maybe the gravity is forceful enough to actually attact the light.
Light has momentum (which "require" mass in more classical thinking). Light is "moved" by gravity (which indicates mass). If mass distorts space so that it makes light and particles behave the same, then why is it a misconception to think of light as a particle? It's both a particle and a wave, thus *is* a particle.
Learn to love Alaska
Not a physicist of any kind, but I had thought that information could not cross the event horizon? If that is true, then how can we construe that the speed of matter near the event horizon indicate the speed of rotation of the black hole? Wouldn't it only indicate the speed of that particular matter? Educate me if I'm wrong!
Most of the Science Channel-style science shows I've seen that cover the issue not only cover that light doesn't escape the gravity well because the gravity of the black hole warps space, but also covered that that's how all gravity works, not just a special variation related to "black holes" as the source or "light" as the affected entity. (As do the more technical, less Science-Channel-ish, works that I've seen addressing the same subject matter.)
The "sucked in" analogy is exactly as accurate (or inaccurate) applied to light as it is to "particles with mass".
In some mediums, light moves faster than it does through a vacuum.
No, it doesn't. Not only does such a material not exist, it is proven beyond any reasonable doubt to be impossible.
c is the speed of light in a vacuumm
Hey! You got something right!
not the "theoretical maximum speed of light"
And right back to wrong. Nothing can travel through space (empty or otherwise) at faster than c, that is the central concept of relativity.
It would be ripped to shreds by tidal and frame dragging forces, heated to millions of degrees by frictional heating, emit some very lively photons, and the resulting plasma would become part of the accretion disc.
And this is assuming you could even get it in place without the same result befalling the construction crew, their equipment, and raw materials.
I can see the fnords!
Oh, and also, you'd never live to see the completion of the object because time dilation caused by the mass of the singularity would cause all motion near the event horizon to slow to a virtual stop, as seen by an observer at a reasonably safe distance.
Of course, you can always go visit it yourself to check on the progress... we won't wait for you, though.
I can see the fnords!
In some mediums, light moves faster than it does through a vacuum.
No, it doesn't. Not only does such a material not exist, it is proven beyond any reasonable doubt to be impossible.
That depends on what exactly you mean with the "speed in the medium".
You certainly can have a phase velocity larger than c, and AFAIK you also can have a group velocity larger than c. What you cannot have is a signal velocity larger than c.
The Tao of math: The numbers you can count are not the real numbers.
For a non-rotating black hole in Schwarzschild coordinates, the radial vector inside the horizon gets timelike, that is, the singularity is not really "in the middle" but "in the future". This quite intuitively explains why you cannot go "outward": The "outward" direction is actually the past direction.
Now, Schwarzschild coordinates are not the full story, but neither are Eddington-Finkelstein coordinates (which obviously are what you had in mind). The complete structure of the Schwarzschild solution can only be seen in Kruskal coordinates, where you on one hand quite literally see that the singularity is in the future (for any world line starting outside the black hole and entering it), but you would still be able to evade it if you could travel faster than light (while in Schwarzschild coordinates it looks as if you'd have to travel backwards in time).
Anyway, light is not "bent towards the middle", that's only the result of non-ideal coordinates where the singularity appears spacelike while it is actually timelike.
For rotating black holes, things are more complicated (there are two horizons, the singularity is spacelike, but not a point, and inside the black hole there occur closed timelike curves).
The Tao of math: The numbers you can count are not the real numbers.
Its local gravity is determined by its rest mass not its relativistic mass.
No. Gravity is determined by the stress-energy tensor, and the energy component is total energy, aka relativistic mass (literally, they're the same thing). Relativistic mass is the gravitational mass is also the inertial mass.
A proton's mass -- the ratio between its acceleration and the force exerted by an electric field -- is much higher than the intrinsic mass of the quarks that make it up. It's the kinetic energy of those quarks held together by the Strong Nuclear Force that gives a proton 90% of its mass. The Higgs Field only explains that last 10%.
Similarly the gravity of the sun is far greater than just the intrinsic mass of the quarks and electrons inside it. It's the sum of all energy in the sun.
If you an accelerate an object it gains energy, and therefore (E=mc^2) relativistic mass, and also therefore increased gravity.
Oh, and yes, this means photons have gravity. Not are affected by gravity (though of course they are) but exert it.
The enemies of Democracy are
Light has momentum (which "require" mass in more classical thinking). Light is "moved" by gravity (which indicates mass)
Also light has energy which is mass in Relativistic thinking, and is moved by (and moves other things by) gravity which is due to it's energy (same as mass).
This is confusing because people think of "mass" as the things photons don't have and matter does (which is true if we mean intrinsic mass), but also think of "mass" as the thing which effects/is affected by gravity and makes objects resist acceleration, when that's actually the relativistic mass (= energy).
It's both a particle and a wave, thus *is* a particle.
A photon is a quantum mechanical particle, which is a thingie which behaves kinda like a classical particle and kinda like a classical wave but not exactly like either.
However the key thing about quantum mechanics is that stuff is quantized... like particles are. So we call them particles. There is no misconception in doing so.
The enemies of Democracy are
In some mediums, light moves faster than it does through a vacuum.
No, it doesn't. Not only does such a material not exist, it is proven beyond any reasonable doubt to be impossible.
Your statement would seem to be contradicted by this theory on faster-than-c speeds between 2 Casimir plates.
c is a constant represents the theoretical maximum speed of light. The problem is that the speed of light is not constant. Light slows down in a medium.
meh, you are almost right.
C is a constant that represents the maximum speed of light *in a vacuum*.
That "in a vacuum" piece is quite important. The medium itself has no effect on the constant c ( constant is a constant), but each medium has its own value of light propagation speed which is *always* less than c.
Think of 'c' as the speed of reality.