greywolf42 <mingstb@marssim-ss.com> wrote in message
news:7ffGd.29$eJ2.20@fe07.usenetserver.com...
<carlip-nospam@physics.ucdavis.edu> wrote in message
news:cs1uci$ose$1@skeeter.ucdavis.edu...
greywolf42 <mingstb@marssim-ss.com> wrote:
[...]
However, observations of accretion disks around masses in excess
of 5 solar masses show quasiperiodic oscillations
Yes.
that require impact with a solid surface.
No. QPOs arise naturally in accretion disks,
Good. Then please describe the physical mechanism. (Hint: None has been
known for 20 years.)
Well, Steve apparantly doesn't know the mechanism.
and certainly do not
require a solid surface. In fact, there are several systems in
which QPO frequencies seem to be related to the characteristic
frequencies of a relativistic orbit: see, for example, Wagoner
et al., Astrophys. J. 559 (2001) L25.
You mean: "'Stable' Quasi-periodic Oscillations and Black Hole Properties
from Diskoseismology"
Abstract: "We compare our calculations of the frequencies of the
fundamental g-, c-, and p-modes of relativistic thin accretion disks
with recent observations of high-frequency quasi-periodic oscillations
(QPOs) in X-ray binaries with black hole candidates. These classes
of modes encompass all adiabatic perturbations of such disks. The
frequencies of these modes depend mainly on the mass and angular
momentum of the black hole; their weak dependence on disk
luminosity is also explicitly indicated. Identifying the recently
discovered, relatively stable QPO pairs with the fundamental g- and
c-modes provides a determination of the mass and angular momentum
of the black hole. ..."
One more for the library run. But "related to the characteristic
frequencies of a relativistic orbit" is not a physical explanation. It's
simply the finding of numerological relationships -- and assuming that
there is a black hole.
Why do you think QPOs "require impact with a solid surface"?
Because no one has a physical explanation without one. And prior
explanations did have solid surfaces -- at least when QPOs were around
accepted neutron stars.
But it's nice to see that someone will finally try to respond to the
issue -- now that a paper has been found that identifies numerological
relationships in orbits.:
From:
http://groups-beta.google.com/group/sci.physics/msg/ca0e3d3753038238
"Hello? Steve? Any Relativists?"
From:
http://groups-beta.google.com/group/sci.physics/msg/d0deef0f9c308d3e
", it does mean this. The signature of such an impact with a solid
surface is called "quasiperiodic oscillations" (QPO) or "quasiperiodic
variations". As has been mentioned many times in these newsgroups over the
years. Always ignored by yourself and the rest of the Relativists. i.e.:
http://www.google.com/groups?selm=ukaqr7gq85sd98%40corp.supernews.com
http://www.google.com/groups?selm=6pcB6.357%243n4.107047%40nntp2.onem...
http://www.google.com/groups?selm=izUI6.48631%24B22.12296337%40news1....
.home.com"
etc.....
Guess I was wrong about any Relativists actually addressing the physics of
QPOs. Throwing a grenade (paper citation) and running seems to be the
normal.....
OK, I've been to the library, and obtained a copy of Wagoner, et al. And I
must back off my claim to pure numerology. However, ad hoc, adjustible
parameters take the place of simple numerology. I also note that Wagoner et
al did not include a test for the null hypothesis -- and did not address any
QPOs from known or suspected neutron stars or white dwarfs. They also
totally fail on half their test cases, and are only marginally successful
with the other half -- even with a huge free parameter to play with.
- - - - - - - - -
"For the past 10 years, our group has investigated the normal modes of
oscillation of standard (geometrically thin) equilibrium models of black
hole accretion disks."
In the real universe, accretion disks are not geometrically thin -- but then
that may simply be a problem in definitions. But it does make for more
tractable math -- if not real applicability. Love that grant money -- 10
years at it so far. ;)
"... We perturb the optically thick, fully relativistic models of Novikov &
Thorne (1973) and Page & Thorne (1974). We have usually considered
accretion disks that are barotropic [p = p(rho)], producing a vanishing
buoyancy frequency. The results below are relatively insensitive to the
value of the viscosity parameter, here taken to be alpha = 0.1. The key
frequencies, associated with free-particle orbits in the disk, are the
rotational [Omega(a,r)], vertical epicyclic [Omega_perp(a,r)], and radial
epicyclic [kappa(a,r)] angular frequencies. The effective inner edge of the
disk is close to the radius r_i(a) of the last stable circular orbit, where
kappa(a, r_i) = 0. For a > 0, which we shall henceforth assume, Omega (r) >
Omega_perp (r) > kappa (r)."
"We stress that linear combinations of these modes should describe all
adiabatic perturbations of such disks. There are essentially three classes
of modes, designated g, c, and p."
{gravitational-inertial, corrugation, and pressure-inertial; respectively}
Simply put (hopefully not too simply) Wagoner at all adjust the
dimensionless angular momentum parameter (a = cJ/GM^2) until they can cause
a match between the 'stable' observations of the QPOs and arbitrary theories
of accretion disk frequencies. Since there is no other effect of the
angular momentum parameter, this is a classic free parameter.
But that in itself does not mean that Wagoner et al are incorrect. What
does indicate that Wagoner et al are incorrect is that the predictions don't
match the observations that they list in their Table 2:
"However, there is an apparent problem with this assignment of themodes.
Since the g-mode occupies a much larger region of the disk (Table 1, a =
0.9), one might expect that the resulting amplitude of the luminosity
modulation would be greater than that of the c-mode if they are excited in
the same manner. This disagrees with the amplitudes in Table 2. However,
since the c-mode is virtually incompressible, it should mainly modulate the
coronal photons via relection from its changing projected area, whereas the
g-mode modulates the internal properties of the disk."
In other words, the math won't show it, but we can wave our arms and make it
go away.....
They close the paper with: "There is not yet evidence that any of the
high-frequency QPOs in other black hole candidates [...] are stable to the
extent required if thy are produced by thes emodes. Some are known to vary
significantly, while others have only been detected during a single
observation."
So Wagoner et al have only been able to "sort-of" explain three out of six
candidates at which they looked (even with an unlimited free parameter).
The other three are outside the model completely.
Steve, when are you going to start reading the actual papers, and not just
the abstracts? It always seems to get you into trouble.
--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}
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