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Fraser
2006-Nov-21, 01:52 AM
Black holes bend our understanding of the Universe and laws of physics. But astronomers have discovered a black hole spinning so quickly, it breaks all the speed laws for rotation. The stellar mass black hole in question is known as GRS1915+105, and it's spinning more than 950 times every second. As the black hole spins, it drags the surrounding space around with it, and gives astronomers an opportunity to study some of Einstein's predictions about relativity.

Read the full blog entry (http://www.universetoday.com/2006/11/20/black-hole-spins-nearly-1000-times-a-second/)

Bojan
2006-Nov-21, 06:00 AM
This is maybe a stupid question, but still...
It is my understanding that the time slows down as the event horizon is approached and actually it stops right there..
How can we then measure the frequency of the rotation of the black hole at the event horizon, when the time flow is stopped at this place? It should be zero....

John Mendenhall
2006-Nov-21, 04:09 PM
If we, as external observers, could drop a clock into the black hole, it would appear to run slower and slower as it approached the event horizon. However, it would at the same time be carried along with everything else that was headed into the black hole. From the external observer's point of view, the clock is moving very fast, approaching c, but is ticking more and more slowly.

Of course, if you are co-moving with the clock, the clock is running normally, but time in the external universe appears to be going faster and faster. Don't try this at home; the tidal forces are disruptive to flesh and bone.

JSemler
2006-Nov-21, 04:59 PM
Why is there a theoretical rotational speed limit for black holes? Can't space be dragged around faster than the speed of light? As you can tell, I'm not theoretically inclined.

What is the difference between this space dragging and the space expansion postulated by the inflationary universe theory? (space expanding faster than the speed of light to solve the flatness of the universe problem?)

I read about this space expansion ideal in the book "The Whole Shebang", Chapter 9 - "The Speed of Space", byTimothy Ferris. This may be the source of my confusion when thinking about space being dragged..

publius
2006-Nov-22, 05:54 AM
The "speed limit" for a rotating black hole is actually the ratio of angular momentum to mass. The language of General Relativity doesn't simplify down to "layman's terms" too easily, and when it is attempted, a lot of stuff gets lost in translation so to speak, and causes a lot of misunderstanding.

There is a limit to the L/M ratio. In the geometrized units, that limit is either 1 or M, I forget (in geometrized units, which GR experts prefer G and c are 1, and everything, including mass has dimensions of length), and right now my mind is working enough to convert that L/M maximum to SI units, but it will involve G and c^2. :)

Anything above that limit would not be a black hole. There would be no event horizon. A so-called "naked singularity" would be possible here, IIRC, but fortunately there's no known physics that could allow anything to hold together rotating that fast compressed down that small. Think of the figure skater pulling her arms in and speeding up. Above the L/M limit, it would fly apart before it could collapse.

And also, when they're speaking of the "rotational speed", they're not talking about any 'w' as we think of it. That's something else that gets lost in translation. The gravitomagnetic field, B_g, has dimensions of frequency, and can be thought of sort of the angular speed space-time is "rotating" at a given point. Rotate at that speed yourself, and you can (locally) transform B_g away. That's what they're talking about.

When a rotating object collapses into a Kerr black hole, the notion of 'w' for the object itself looses meaning. The only thing you can know is L and M.

-Richard

GOURDHEAD
2006-Nov-22, 01:56 PM
I assume the Lens-Thirring effect is manifested in such conditions and space-time (or is it only space) gets wrapped around the axis of rotation which "compresses" the nearby space and stretches volumes of space located farther away from the axis of rotation. If so, this should render the local environment unstable by aportioning undue amounts of potential energy to the Lens-Thirring affected space and result in ripping space and generating an uncommon explosion. If I'm lucky, all of what I just wrote is nonsense.

joedoe
2006-Nov-23, 02:38 AM
WOW!!!

60,000 rpm WOW!! :eh:

hang on :think:

must be made of Outlandish matter compressed twice over and baked on high for an hour :doh: :dance: it also must gain it's energy by feeding of a invisible dark matter/energy companion :shhh: :p

1000 rps WOW!


really we have no idea do we :question: (well some might) LINK (http://www.holoscience.com/views/view_strange.htm)



The Nobel Laureate, Irving Langmuir, coined the term "pathological science" for "the science of things that aren't so".

Two key symptoms of such science are:
(1) the resort to fantastic theories contrary to our experience, and
(2) the use of ad-hoc requirements to save the appearances.

If we apply these criteria, two disciplines that share line honours for pathological or strange science are cosmology and particle physics. They both deal with unseen objects - neutron stars, black holes, quarks, etc. They both produce fantastic ad-hoc requirements to explain new discoveries - dark matter, super-heavy objects and exotic particles. They cross-infect each other with their theoretical requirements both to save appearances and convince governments to spend large sums of research money for super-colliders to replay bits of a hypothetical Big Bang, or to build gravity-wave telescopes when we have no proof such waves exist. The above report brings such strange science sharply into focus.

It is not ordinary matter, but scientific models that are being pushed to extremes. Einstein warned: "Most mistakes in philosophy and logic occur because the human mind is apt to take the symbol for reality". Neutron stars and quarks have never been seen. They are derived from mathematical symbols. Let's take quarks first. There is little to suggest that any of the shrapnel from high energy colliders exists in normal matter. If enormous energy is spent in shattering a proton to unlock the hypothetical quarks then the energy itself may manifest as particles that don't play any part in ordinary matter. Flying a 747 into a mountainside and picking over the ruins is not the best way of finding out how an aircraft works. Suggesting that a star can be composed stably of unobserved particles simply because a theory of invisible, super-heavy objects demands it is asking too much!

antoniseb
2006-Nov-23, 02:43 AM
it also must gain it's energy by feeding of a invisible dark matter/energy companion

No, there's no need for that. BTW, dark matter/energy do not collect into 'companions'.

publiusr
2006-Dec-22, 06:03 PM
If only we could turn it into a giant generator.