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Astrophysics/angular momentum of a black hole

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Expert: - 1/31/2011


Question
Your Question was:

why is the maximum angular momentum of a black hole limited to   
G * M^ 2 / c.?

Answer
Hello,

The key aspect to consider here is that a black hole assigned some mass M can’t have any arbitrary L (angular momentum). (Else the singularity falls outside the event horizon- which is nonsense!)  Instead a specific inequality needs to be satisfied:

(GM/c)^2  > or =   G(Q/c)^2 + (L/M)^2

Let Q (charge) = 0 as a limiting case, then:

(GM/c)^2  (> or =)    (L/M)^2

And:


L^2 =  M^2 (GM/c)^2  

Then, for L(max):

L(max) = [M^2 (GM/c)^2 ]^1/2

L(max) = M * GM/c =  GM^2/c

Hope this helps!

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Volunteer

Philip A. Stahl

Expertise

I specialize in stellar and solar astrophysics. Can answer any questions pertaining to these areas, the spectroscopic analysis of stars – as well as the magneto-hydrodynamics of sunspots and solar flares. Sorry – No homework problems done or research projects! I will provide hints on solutions.

Experience

Have published papers on the relationship between sunspot morphology and solar flares; discovery of SID flares related to this, constructed computerized stellar models; MHD research.

Organizations
American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.

Publications
Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France). Books: 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level'.

Education/Credentials
B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.

Awards and Honors
Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society

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