What is Kerr: Definition and 95 Discussions

KERR (750 AM, "KERR Country") is a radio station licensed to serve Polson, Montana. The station is owned by Anderson Radio Broadcasting, Inc. It airs a country music format.The station was assigned the KERR call letters by the Federal Communications Commission.KERR is Montana's primary entry point station for the Emergency Alert System.

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  1. Y

    CTCs in Kerr Metric: Examining the Invariance of CTCs in Spacetime

    Are CTCs in the Kerr metric just an artefact of the coordinates used? This paper http://arxiv.org/abs/gr-qc/0207014 suggests that is the case. In a private message it has been suggested to me that CTCs in a spacetime are an invariant feature so are not removable by a change of coordinate system...
  2. A

    Exploring the Kerr Optical Effect: λ & E Parameters

    I'm wondering about the Kerr Optical effect as described on wikipedia: http://en.wikipedia.org/wiki/Kerr_effect Are there limits to the range of parameters at which the effect starts to break down? What λ values and E values does this formula apply to?
  3. S

    Demonstrating Metric Kerr Expression

    hi , how i can demonstrate the expression of metric kerr?
  4. C

    Area of event horizon and irreversible mass of Kerr black hole

    Hi everyone, and happy new year if you happen to be reading this tomorrow. Rather than partying, I am writing up 100+ pages of astrophysics lecture notes, which I think will take infinite time as I keep getting stuck on every other line. My current problem is with the equation for the...
  5. cosmik debris

    Roy Kerr awarded Einstein Medal

    http://www.stuff.co.nz/science/8101704/Einstein-Medal-for-NZ-professor
  6. G

    Shape of Kerr event horizon in terms of reduced circumference

    The event horizon of a Kerr black hole is often depicted as being spherical, but this seems to be a reference to the horizon as defined in Boyer-Lindquist coordinates, where horizons appear at a constant value of r. However, Thorne describes the "black hole's horizon bulg[ing] out at its...
  7. S

    Slow-rotation weak-field limit of Kerr

    Hi all, I want to know if slow-rotation weak-field limit of Kerr metric is also acceptable for the Earth situation or not. It has been shown that in this limit, Kerr metric is reduced to Schwarzschild metric plus a cross term that indicates rotation. So thanks in advance, Saeide
  8. D

    Null geodesics of a Kerr black hole

    Homework Statement Hi, From the Kerr metric, in geometrized units, \left(1 - \frac{2M}{r}\right) \left(\frac{dt}{d\lambda}\right)^2 + \frac{4Ma}{r} \frac{dt}{d\lambda}\frac{d\phi}{d\lambda} - \frac{r^2}{\Delta} \left(\frac{dr}{d\lambda}\right)^2 - R_a^2...
  9. D

    Computer plot of particle orbits around Kerr black holes

    Hi there, First post, so be gentle. I'm currently doing a project on Kerr black holes, part of which is based on a project in Edwin F. Taylor's book "Exploring Black Holes" (the chapter is found here) as well as some of Hartle's book (chapter 15). Part of my project, and as a way of better...
  10. D

    Time Travel - Between two Kerr metric black holes w/detached event horizons

    So imagine your on Earth at a latitude of 30 to 45° N, between two rotating Kerr Metric Blackholes with detached event horizons (dual singularities) allowing you to be shielded from the crushing force of the black holes. Which way do the rotating black holes need to rotate for the past and...
  11. T

    D'Inverno Ch 19 - Kerr Solution

    I've tried to work my way through section 19.2 but have run into a problem at the very end. I've attached a PDF with the Jacobian I used for the transformation and a description of what has gone wrong. What does D'Inverno mean when he says 'if we require v' and r' to be real' ? you can...
  12. E

    Radius of Ring Singularity in Kerr Black Hole

    I researched this some, but could not find a method to calculate the radius of the ring singularity in a Kerr black hole. I would think it is a function only of black hole mass and angular velocity. Please let me know if there is some reports or papers on this.
  13. apeiron

    CP violation explained by Kerr metric

    This is an interesting hypothesis that doesn't seem to have been discussed yet. What are its flaws? Mark Hadley at the University of Warwick argues that galactic rotation causes gravitational frame-dragging sufficient to put a local asymmetric twist into spacetime and explain observed CP...
  14. jfy4

    Electron Falling in Kerr Metric: Release of 40% Rest Energy?

    I have here a quote from Hartle's Gravity, page 321: "The fraction of rest energy that can be released in making a transition from an unbound orbit far from an extremal black hole to the most bound innermost stable circular orbit is (1-1/\sqrt{3})\approx 42\%". My question is about...
  15. Y

    How to obtain Kerr Metric via Spinors (N-P Formalism)

    How to obtain Kerr Metric via Spinors (Newman-Penrose Formalism)? I am a bit confused with Ray d'Inverno's Book. Why perform the coordinates transformation: 2r-1 -> r-1 + r*-1 I am bit confused of it. And I am a bit confused, too, of how to write out null tetrad...
  16. D

    Big trouble with Kerr solution

    'Ideal' schwarzschild solution is for an eternal black hole. It also includes a 'white hole' part, which is excluded, or course, from a 'realistic' collapse solution. What's about the kerr solution? Inside kerr black hole there is ring with enougmous frame dragging around it, so strong, that...
  17. L

    Kerr Metric Confusion: Problem 1 on Page 138

    Hi. I'm trying problem 1 on p138 of this http://arxiv.org/PS_cache/gr-qc/pdf/9707/9707012v1.pdf Now when I try and get the Euler Lagrange equation for \phi I get (the Kerr metric in BL coordinates can be found at the bottom of p77) \frac{\partial L}{\partial \phi} = \frac{d}{d \tau}...
  18. I

    Dark matter, dark energy, and the Kerr metric?

    I’m sorry, but I find dark matter and dark energy problematic. It’s hard to think of a Universe made up of about 95 % of stuff we have no idea about, except that maybe dark matter and dark energy have some properties. So I’m thinking maybe there’s something wrong with the data, but I can’t...
  19. Z

    What are physics constant in Kerr metric?

    1. What are the value of physics constant in Kerr metric, including G, M, c, a, r, or others? I expect to simplify Gamma 2. why g_compts[1,4] has element and not [4,1]? 3. Some book assume G = c = 1, what is the meaning of this setting? 4. Different material have different metric, are...
  20. E

    Question about Killing vectors in the Kerr Metric

    Hi, I'm a physics undergrad working through Carroll at the moment. In the section on the Kerr black hole, he states that K= \partial_t is a Killing vector because the coefficients of the metric are independent of t. He then states in eq. 6.83 that K^\mu is normalized by: K^\mu K_\mu = -...
  21. B

    What Molecules Can be Used for Research on Kerr Effect and Why?

    Homework Statement I what to do a summer physics project on Kerr effect. I want to determine Kerr constant for some molecules. Problem is that i cannot get nitro-benzene and nitro-toluene. Therefor i need to do my research on some other molecules, problem is that i don't have mentor who...
  22. S

    Kerr metric derivation (Adler, Bazin & Schiffer)

    I have a problem understanding part of Adler, Bazin and Schiffer's (Introduction to General Relativity 2nd Edition) derivation of the Kerr metric. I would be grateful if someone could explain where I am going wrong. My problem concerns the transition from the O(m2) equation (7.15b) to (7.24)...
  23. stevebd1

    What is the equation for stable orbits in Kerr metric?

    The equation for the surface gravity of a black hole in Kerr metric is- \kappa_\pm=\frac{r_\pm-r_\mp}{2(r_\pm^2+a^2)} where r+ is the outer event horizon- r_+=M+\sqrt(M^2-a^2), r- is the inner event horizon- r_-=M-\sqrt(M^2-a^2) and a is the spin parameter in metres- a=J/mc. An exact...
  24. U

    How can I easily study the derivation of Kerr Metric?

    Hello friends.I study about Kerr metric and black holes.I can deriving Schwarzschild metric basically but i can't derive the Kerr metric. Anyone know how can i study it with basic concepts? please suggest to me any lecture note or text. thanks.
  25. Jorrie

    Accelerations in Kerr Metric

    Pervect has https://www.physicsforums.com/showpost.php?p=1046874&postcount=17" for radial and tangential gravitational accelerations of a moving particle in Schwarzschild coordinates. \frac{d^2 r}{d t^2} = \frac {3 m{{\it v_r}}^{2}}{ \left( r-2\,m \right) r} + \left( r-2\,m \right)...
  26. stevebd1

    Kerr Black Hole & Keplerian Stable Orbit

    The following is the equation for a Keplerian stable orbit at the equator around a Kerr black hole- \tag{1}v_s=\frac{\pm\sqrt{M}(r^2\mp2a\sqrt{Mr}+a^2 )}{\sqrt{\Delta}(r^{3/2}\pm a\sqrt{M})} where M=Gm/c^2,\ a=J/mc and \Delta=r^2-2Mr+a^2 which for a static black hole would reduce to -...
  27. D

    What is the Orientation of Lightcones in a Kerr Ring?

    I am trying to find any diagrams like the following ones: http://www.valdostamuseum.org/hamsmith/DFblackIn.gif http://www.illc.uva.nl/~seop/entries/sp ... one-bh.gif http://www.orbiter-forum.com/gallery/da ... ration.jpg (the 1st is the best, even I failed to find it in better...
  28. J

    Schwarzschild & Kerr black holes geometries

    Hello Let's consider a Schwarzschild BH. A photon (or a massive particle) crossing the event horizon cannot be static : the r (radial) coordinate becomes a temporal coordinate. Therefore, the photon falls towards the central singularity (r=0). There is no way for him to escape : the...
  29. stevebd1

    Killing surface gravity for a Kerr black hole

    From wikipedia 'http://en.wikipedia.org/wiki/Surface_gravity" '- For a static black hole, this is- \kappa=\frac{c^2}{4M}=\frac{c^2}{2r_s} where M=Gm/c^2 and rs is the Schwarzschild radius (2M) this is synonymous to Newtons equation for gravity g=Gm/r^2 at the event horizon where r=2M (the...
  30. R

    Gravitational Redshift for Photon around Kerr Black Hole

    I have a hopefully straightforward question. It is well known that in the Schwarzschild metric the gravitational redshift is given by 1+z=(1-r_{s}/r)^{-1/2}. Clearly this is just the ratio of observed to emitted frequencies (or energies). I understand this so far. However, for the case of the...
  31. R

    Kerr metric, singularities in Boyer-Lindquist and Cartesian coordinates

    I've found a fairly concise review of the Kerr metric at http://www.physics.mcmaster.ca/phys3a03/The%20Kerr%20Metric.ppt The Kerr Metric for Rotating, Electrically Neutral Black Holes: The Most Common Case of Black Hole Geometry. Ben Criger and Chad Daley. On slide 6 they give the usual...
  32. R

    Ring -singularity (Determinant of the Kerr metric)

    "Ring"-singularity (Determinant of the Kerr metric) My problem is as follows: "Calculate the determinant of the Kerr metric. Locate the plac where it is infinite. (In fact, this gives the "ring"-singularity och the Kerr black hole, which is the only one) I got the determinant to ...
  33. J

    What distinguishes Kerr and Schwarzschild blackholes?

    Consider the Schwarzschild black hole vacuum solution. Now let a test particle drop from "coordinate rest" at a finite r, and watch it fall in. Is there a coordinate transformation in which we go to a rotating frame where the black hole is now a Kerr black hole and the test particle follows...
  34. C

    Can Kerr Black Holes be Detected Through Gravitational Lensing Experiments?

    Hello, i was studying kerr black holes and i think i can understand most of the theory behind it but i was wondering how can you detect black holes that are actually rotating?. I thought like sending two light rays from the same point (like gravitational lensing) but since the black hole is...
  35. H

    Extremal Kerr Black holes, and their associated temperature.

    So I was calculating the temperature for a extremal Kerr black hole. G2*M2 = a2, where a = J/m. Using T = kappa / 2 /Pi... I'm assuming this is the correct approach. But my question is... The surface gravity of an extremal Kerr black hole appears to be zero, leading to a zero temperature...
  36. Orion1

    Kerr metric hydrostatic equilibrium

    I basically understand how the Tolman-Oppenheimer-Volkoff equation for hydrostatic equilibrium was derived from the Schwarzschild metric in General Relativity and from the equation derivatives listed. However, when I attempt to derive the equation derivatives for the Kerr metric, I obtain these...
  37. M

    Lab work: measuring Kerr effect

    Homework Statement the main idea is this i have an 'Alternate current' I which i know the intensity I have also 2 Helmholtz plates of radius 'R' separated by a distance 'R' (the separation between plates is equal to their radius ) then by magnetic induction the alternate current 'I' we...
  38. Orion1

    Understanding the Kerr Metric: Solving for Delta and Lambda functions

    According to Wikipedia, the equation for the Kerr metric is: c^{2} d\tau^{2} = \left( 1 - \frac{r_{s} r}{\rho^{2}} \right) c^{2} dt^{2} - \frac{\rho^{2}}{\Lambda^{2}} dr^{2} - \rho^{2} d\theta^{2} - \left( r^{2} + \alpha^{2} + \frac{r_{s} r \alpha^{2}}{\rho^{2}} \sin^{2} \theta \right) \sin^{2}...
  39. A

    Can one diagonalize the Kerr metric?

    Is it possible to diagonalize the Kerr metric in the Boyer-Lindquist coordinates? If so then I think calculations with the metric will become easier. I forget under what condition a matrix can be diagonalized. Can anybody remind me?
  40. michael879

    Two Kerr Black Holes: Possible or Impossible?

    Im trying to describe a system of two kerr black holes and I was wondering if this was even possible? I am currently taking a GR course but I've looked through the textbook and we only seem to deal with stationary solutions to einstein's field question (and no two-body problems).
  41. stevebd1

    Cauchy horizon in a Kerr rotating black hole

    I'm currently in the process of understanding the properties of the Cauchy (or inner event) horizon in a rotating Kerr black hole. Initially, I thought the horizon was a result of centrifugal forces from the rotating ring singularity and extreme frame dragging that forced matter outwards...
  42. D

    Kerr solution as complex transformation

    I've been reading Ray D'Inverno's book about general relativity, and when he derives the Kerr metric he uses a trick with a complex transformation. I can follow the derivation, but I have no clue why it works. Anyone care to explain? The derivation is: They start with schwarzchild in...
  43. C

    What does Roy Kerr's new eprint reveal about the interior of black holes?

    A new eprint by Roy Kerr has just appeared on the arXiv, which should be of extraordinary interest to all PF members interested in black holes: http://www.arxiv.org/abs/0706.1109 Picking up the theme that Wikipedia may be destroying the very notion of truth as I know it, Kerr explicitly...
  44. S

    Kerr Pre-Measurement vs Bell's Inequality

    I have a question, after having read about a non-destructive spin measurement experiment, which was cited as one of the top science stories of 2006: http://physicsweb.org/articles/news/10/12/15/1#11...
  45. V

    Finding a Kerr Metric Using the Einstein Equation

    How can I obtain a Kerr metric by using the Einstein equation?
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