Re: Why don't we see star formation at the edges of black holes?

[Roger Haar <haar@PHYSICS.ARIZONA.EDU>]

Lee
        You are asking a number of interesting and in fact difficult
questions.
The full answer to some of these question require advanced college courses.

        Concerning stars formation near black holes:  Most black holes are
relatively small ( no more than a few tens of solar masses) and the matter
that is falling in is coming from a binary companion star.  The infall rate
is very small. I think the order of a few millionths of a solar mass per
year.  I do not think there is enough mass near the event  horizon at any
one time to create a star.  The huge black holes assumed to be at the
galactic core long ago sucked in most of the surrounding matter that is easy
to get.  Most of the surrounding matter goes into orbit about these black
holes.  Some of the star formation in the galactic core probably is related
to  strong gravitational fields,  but near the event horizon the actual
density of matter is relatively low.

        Concerning the formation of neutron star:  In a star collapsing into
a neutron star the gravitational force dominate the electrical forces.  Even
though the electromagnetic force is 10^40 times stronger in some fundamental
way, each atom is electrically neutral and thus produce little long-range
repulsion, but the gravitational force basically involves every other atom
in the star.  Thus the total gravitational force is huge.  This creates high
pressures and high temperatures.  The nuclei  get pushed closer together,
until the electrons start spending more and more time inside one nucleus or
another. The nice orbits of electrons around a single nuclei for an isolated
atom have long since broken down. The whole star acts like a solid in which
the electrons shared by a large number of nuclei.   The electrons eventually
interact with a proton to form a neutron, in part because of they spend so
much time inside some nucleus.  This further reduces the electoral
repulsion.  Again, I think the missing link in your understanding may have
been the neutralization of the electrical forces compared to the additive
nature of the grativtational attraction.

        Concerning reflection:   Light  (photons) can collide and be
reflected from electrons without an absorption and re-emission.  This would
be Compton scattering, but this is not the cause of normal reflections.  In
the normal interaction of light reflecting off of a surface.  Light
interacts with a bulk of the material, not just one atom.  These interacts
are not simple, which explains why this interaction almost never is
discussed in terms of quantum mechanics.  Compared to a single atom, visible
light is huge:
        Atom is about 0.1  nm in diameter
        Visible light has a wavelength of about  500 nm wavelength,
                           and length of the photon also called a coherence
length  is
                            usually tens of micrometer.

Thanks
Roger Haar

*************************************************
"Lee W. Lerner" wrote:

> Is there an explanation for the lack of star formation at the boundaries
> of black holes.  It seems that with the tremendous gravitational
> influence of a black hole that matter streaming toward it wouldn undergo
> severe gravitational compression -- enough to form protostars.  It seems
> reasonable that we should observe lots of nebula like conditions as we
> approach the event horizon.  Is there an explanation based on what
> happens to particles as they are accelerated toward the event horizon.
>
> Lee Wilmoth Lerner
> Fairhope High School, Fairhope, AL USA                        Email via:
> lw.lerner@juno.com
>  “But I don't have to know an answer.  I don't feel frightened by not
> knowing things,
> by being lost  in the mysterious universe....” -- Richard Feynman
> "...unless, of course, I have a test" -- LWL
>
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