Re: [NTLK] OT Trolls and black holes

From: Eric L. Strobel (fyzycyst_at_comcast.net)
Date: Tue Jul 09 2002 - 09:39:30 EDT


on 7/9/02 6:35 AM, Jochen Sch=E4fer at js.josch_at_gmx.de wrote:

>=20
>=20
> ----- Original Message -----
> From: "L vRooy" <ara_at_dwaf.pwv.gov.za>
> To: <newtontalk_at_newtontalk.net>
> Sent: Tuesday, July 09, 2002 10:50 AM
> Subject: Re: [NTLK] OT Trolls and black holes
>=20
>=20
>>=20
>> Jochen wrote
>> --But you're right, the black hole itself doesn't get
>> --bigger, only heavier.
>>=20
>> This means matter is infinely compressible?
> AFAIK, the mathematical model predicts that a black hole is a singularity,
> so you can say that matter is infinitely compressible. But that's only a
> description, of course.
>> How far from the event horizon does this singularity exists (variable of
> course)? The pictures usually show this as a vortex shape, does the formu=
las
> predict that?
> Einstein predicted that gravity generally distorts space-time with the bo=
dy
> in the middle of the distortion. Other bodies then move around the
> distortion in circles (more or less) like classical or Newtonian physics
> predict.
> If you have a black hole this distortion of space-time is so big that the
> mass is compressed in a singularity and even light can't escape.
>=20
>>=20
>> excuzatti if this is a bit 1st y college Q.s
> If this is of interest for you, you should consider reading "A little
> history of Time" by S. Hawkings.
>=20

OK... *cracks knuckles*

"Black holes have no hair..." -> The only properties one can discern about a
black hole are: mass, angular momentum (spin), and charge. As a consequence
of Hawking radiation, one can also obtain a temperature (and therefore an
entropy). No other distinguishing characteristics ("hair") are possible.
{Although there's been some interesting work being done by the information
theorists... But that's mostly over my head.}

The size and shape of the event horizon are determined by mass, spin and
charge. As mass grows the size of the event horizon grows, spin will
distort the spherical event horizon (with fast enough spin it can even
become toroidal!), and I forget just what effect the charge has on the
shape/size...=20=20

The "whirlpool" that is often shown is the accretion disk. Since black
holes don't 'suck' anything in, passing objects simply continue to follow
the laws of orbital motion as physicists know them (recall that orbits for
GPS satellites are calculated including general relativity effects). {Some
of the effects include precession of the perihelion (where long axis of the
elliptical orbit rotates around the central object), gravitational
redshift/time dilation, and even frame dragging (where, essentially, space
itself it being pulled along by the rotation of the central object). Now,
tidal forces or interactions with a third object, can shed enough energy for
an object to end up in orbit. If the object passes close enough to the BH,
it can get ripped apart. You end up with a situation where all this
'debris' (gas and stuff) is on a whole bunch of orbits. Since every stellar
system forms with some overall spin, this will determine a favored plane
where much of the material is (this is also true, obviously, for the central
BH in our galaxy). So the debris would tend to form a disk. Once a disk is
formed, the effect of collisions (and the disk's gravity) would tend bring
out of plane material into the disk. Material on the inside of the disk
will be getting ever hotter from collisions, etc. and will be radiating
energy away (we see this with x-ray telescopes) and also will be losing
orbital energy in the form of gravity waves. Eventually this material will
spiral into the BH.

"Infinite compressibility" -> This is the equivalent of the ornate pointing
hand on ancient maps, emblazoned with the legend "Here be dragons." The
singularity is a byproduct of what we might call 'classical' general
relativity. Long before things reach the state of infinite density, quantum
gravity and theories of everything begin to rear their heads. There's been
some promising progress in these areas, but as yet, nobody really knows how
to calculate just what happens as we approach "singularity".

Did I leave anything out??? :-)

- Eric.
--=20

Eric Strobel (fyzycyst_at_NOSPAM^mailaps.org)

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
What if the 'Hokey-Pokey' really IS what it's all about??
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=20

-- 
Read the List FAQ/Etiquette: http://www.newtontalk.net/faq.html
Read the Newton FAQ: http://www.guns-media.com/mirrors/newton/faq/
This is the NewtonTalk mailing list - http://www.newtontalk.net



This archive was generated by hypermail 2.1.2 : Thu Aug 01 2002 - 06:02:16 EDT