accretion/event horizon

just reading about the chandra observations of the event horizons of
xray novae. whilst reading it a question came to mind; have all the
previous 'observations' of black holes been based only upon the
observing of relative motions created by the enormous densities that
define black holes? have we not directly seen structures of the black
holes themselves until this point? what about jets like m87 (?) that
come to mind; wouldnt we be able to discern where the event horizon
would be there, or are we not certain that is a black hole?
excuse the ignorance and thanks in advance.

-e.

wrote:
just reading about the chandra observations of the event horizons of
xray novae. whilst reading it a question came to mind; have all the
previous 'observations' of black holes been based only upon the
observing of relative motions created by the enormous densities that
define black holes? have we not directly seen structures of the black
holes themselves until this point? what about jets like m87 (?) that
come to mind; wouldnt we be able to discern where the event horizon
would be there, or are we not certain that is a black hole?
excuse the ignorance and thanks in advance.

-e.


What has been observed are phenomena that are modeled (some say best modeled) by
a black hole. In the case of x-rays coming from what appear to be normal stars,
the model in some cases is a black hole orbiting that star and the x-rays coming
from an accretion disk around it. In the case of the active cores of galaxies,
the best model consistent with the observations (and our current understanding
of physics) is a black hole, supermassive in this case (millions to 100's of
millions of solar masses or more), again with an accretion disk orbiting around
it. There have even been observations hinting at detecting the central
accretion disk.

But, in all of those cases reported so far, all that is said is that the best
model for explaining the observed phenomenon, whatever it is, is a black hole
interacting in some way with its environment. We have not observed directly a
black hole or its event horizon (go back and check the wording on the Chandra
announcement).

So, the correct assessment is that we have plenty of candidates that might best
be explained as the result of a black hole.

"s" == spiderrescue writes:

s just reading about the chandra observations of the event horizons
s of xray novae. whilst reading it a question came to mind; have all
s the previous 'observations' of black holes been based only upon the
s observing of relative motions created by the enormous densities
s that define black holes?

I'd phrase it as something like the following. Assuming that general
relativity is the correct description of gravity (at least on
macroscopic scales), the motions of gas or stars in the neighborhood
of certain dark objects is only consistent with those objects being
black holes.

In other words, their presence has been inferred not observed directly.

s have we not directly seen structures of the black holes themselves
s until this point? what about jets like m87 (?) that come to mind;
s wouldnt we be able to discern where the event horizon would be
s there, or are we not certain that is a black hole?

The future may be different. There are plans to use the technique of
very long baseline interferometry (VLBI) at sub-millimeter wavelengths
to image the neighborhood of the object Sgr A* at the center of the
Milky Way Galaxy. If everything works, the observations should be
able to detect the "shadow" of the black hole against its accretion
disk. See Volume 18 of GCNEWS,
URL:http://www.aoc.nrao.edu/~gcnews/gcnews/Vol.18/gcnews.shtml.

--
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No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

greywolf42 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, 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.

Why do you think QPOs "require impact with a solid surface"?

Steve Carlip

wrote in message
...
greywolf42 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.)

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/...0e3d3753038238
"Hello? Steve? Any Relativists?"

From:
http://groups-beta.google.com/group/...deef0f9c308d3e

", 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=uk....supernews.com
http://www.google.com/groups?selm=6p...7%40nntp2.onem...
http://www.google.com/groups?selm=iz...296337%40news1....
..home.com"

etc.....

--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}

"g" == greywolf42 writes:

g Joseph Lazio wrote in message
g ...

s [regarding X-ray novae, Chandra observations, and event horizons]

I'd phrase it as something like the following. Assuming that
general relativity is the correct description of gravity (...), the
motions of gas or stars in the neighborhood of certain dark objects
is only consistent with those objects being black holes.

In other words, their presence has been inferred not observed
directly.

g However, observations of accretion disks around masses in excess of
g 5 solar masses show quasiperiodic oscillations that require impact
g with a solid surface. In other words, the data shows that these
g are neutron stars, not the black holes required by GR.

I'll certainly defer to Steve Carlip, but that is not my
understanding.

Quasi-periodic oscillations (QPOs) have been seen from accreting white
dwarfs, neutron stars, and black hole candidates. What is *not* seen
from black hole candidates are Type I X-ray bursts. This has been
interpreted (most notably by Ramesh Narayan) as evidence that black
hole candidates lack a surface, i.e., that they have an event horizon.


s have we not directly seen structures of the black holes themselves
s until this point? [...]

The future may be different. There are plans to use the technique
of very long baseline interferometry (VLBI) at sub-millimeter
wavelengths to image the neighborhood of the object Sgr A* at the
center of the Milky Way Galaxy. If everything works, the
observations should be able to detect the "shadow" of the black
hole against its accretion disk. See Volume 18 of GCNEWS,
URL:http://www.aoc.nrao.edu/~gcnews/gcnews/Vol.18/gcnews.shtml.

g This would not discriminate between a black hole and a neutron
g star. And since it hasn't happened yet, it isn't support even for
g a neutron star.

A variety of measurements---stellar motions, gas motions, and the
(lack of) the proper motion of Sgr A*---all indicate that the mass of
Sgr A* is well above the limiting mass for a neutron star.


g As contrary data (i.e. stars that ignore the presumed "black hole")
g is simply ignored.

References are notably lacking. For the casual reader, visit
URL:http://adsabs.harvard.edu/abstract_service.html and type either
"Ghez" or "Genzel" into the author query box. These two (Andrea Ghez
and Reinhard Genzel) have been among the leaders in measuring stellar
motions within the central regions of Sgr A*. I've heard Ghez and/or
Genzel's collaborators speak a couple of times about their
observations. They are quite interested in finding motions that would
not be consistent with simple Keplerian orbits. Last I heard, all of
the motions are quite consistent with simple Keplerian motion about a
dark mass of roughly 4 million solar masses.

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Joseph Lazio wrote in message
...
"g" == greywolf42 writes:

g Joseph Lazio wrote in message
g ...

s [regarding X-ray novae, Chandra observations, and event horizons]

I'd phrase it as something like the following. Assuming that
general relativity is the correct description of gravity (...), the
motions of gas or stars in the neighborhood of certain dark objects
is only consistent with those objects being black holes.

In other words, their presence has been inferred not observed
directly.

g However, observations of accretion disks around masses in excess of
g 5 solar masses show quasiperiodic oscillations that require impact
g with a solid surface. In other words, the data shows that these
g are neutron stars, not the black holes required by GR.

I'll certainly defer to Steve Carlip, but that is not my
understanding.

Deference is useless. The understanding (if any) should be based upon the
scientific method. Let's see how you get there.

Quasi-periodic oscillations (QPOs) have been seen from accreting white
dwarfs, neutron stars, and black hole candidates. What is *not* seen
from black hole candidates are Type I X-ray bursts. This has been
interpreted (most notably by Ramesh Narayan) as evidence that black
hole candidates lack a surface, i.e., that they have an event horizon.

And QPO's themselves are direct, positive evidence for a solid surface. In
short, you are arguing that lack of any reporting of one effect (X-ray
bursts) cancels all direct observations of another effect. X-ray bursts are
uncommon (even theoretically). QPOs are common.

I do not accept the validity of Ramesh's logic. What is *your*
interpretation? Can the lack of a report of one observation obviate a
multitude of other, direct observations?

s have we not directly seen structures of the black holes themselves
s until this point? [...]

The future may be different. There are plans to use the technique
of very long baseline interferometry (VLBI) at sub-millimeter
wavelengths to image the neighborhood of the object Sgr A* at the
center of the Milky Way Galaxy. If everything works, the
observations should be able to detect the "shadow" of the black
hole against its accretion disk. See Volume 18 of GCNEWS,
URL:http://www.aoc.nrao.edu/~gcnews/gcnews/Vol.18/gcnews.shtml.

g This would not discriminate between a black hole and a neutron
g star. And since it hasn't happened yet, it isn't support even for
g a neutron star.

A variety of measurements---stellar motions, gas motions, and the
(lack of) the proper motion of Sgr A*---all indicate that the mass of
Sgr A* is well above the limiting mass for a neutron star.

But that is simply GR theory. We are looking for direct evidence.

g As contrary data (i.e. stars that ignore the presumed "black hole")
g is simply ignored.

References are notably lacking.

Why should I repeat myself, Joseph? *You* certainly didn't provide any
references to support your view.

For the casual reader, visit
URL:http://adsabs.harvard.edu/abstract_service.html and type either
"Ghez" or "Genzel" into the author query box. These two (Andrea Ghez
and Reinhard Genzel) have been among the leaders in measuring stellar
motions within the central regions of Sgr A*. I've heard Ghez and/or
Genzel's collaborators speak a couple of times about their
observations. They are quite interested in finding motions that would
not be consistent with simple Keplerian orbits.

LOL! And they show their "interest" by throwing out any data that don't fit
the "massive black hole" assumption.

Last I heard, all of
the motions are quite consistent with simple Keplerian motion about a
dark mass of roughly 4 million solar masses.

That's because your memory is selective, Joseph. As in the thread "Galaxies
without dark matter halos", in which you and I (and others) discussed this
very problem -- with references.

http://groups-beta.google.com/group/...7262911cec7a18
http://groups-beta.google.com/group/...2e12a11f767787
http://groups-beta.google.com/group/...d6bc953cdd7496

--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}

"g" == greywolf42 writes:

g Joseph Lazio wrote in message
g ...

s [regarding X-ray novae, Chandra observations, and event horizons]

g observations of accretion disks around masses in excess of 5 solar
g masses show quasiperiodic oscillations that require impact with a
g solid surface. In other words, the data shows that these are
g neutron stars, not the black holes required by GR.

I'll certainly defer to Steve Carlip, but that is not my
understanding.

g Deference is useless. The understanding (if any) should be based
g upon the scientific method.

Understanding often also depends on the amount of time that one has
spent working on a problem. Steve has considerably more experience
working on problems in general relativity than do I. If we disagree,
it is more likely that I am in the one in error, or I defer to Steve's
experience.

Quasi-periodic oscillations (QPOs) have been seen from accreting
white dwarfs, neutron stars, and black hole candidates. What is
*not* seen from black hole candidates are Type I X-ray bursts.
This has been interpreted (most notably by Ramesh Narayan) as
evidence that black hole candidates lack a surface, i.e., that they
have an event horizon.

g And QPO's themselves are direct, positive evidence for a solid
g surface. In short, you are arguing that lack of any reporting of
g one effect (X-ray bursts) cancels all direct observations of
g another effect. X-ray bursts are uncommon (even theoretically).
g QPOs are common.

My first two sentences are observational results, as anybody who does
a quick search of ADS can attest.

The statement that QPOs are positive evidence for a solid surface is
an inference, for which you have provided no evidence.

g I do not accept the validity of Ramesh's logic. What is *your*
g interpretation? Can the lack of a report of one observation
g obviate a multitude of other, direct observations?

You've provided no support for your assertion that QPOs indicate a
solid surface.

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Joseph Lazio wrote in message
...
"g" == greywolf42 writes:

g Joseph Lazio wrote in message
g ...

s [regarding X-ray novae, Chandra observations, and event horizons]

g observations of accretion disks around masses in excess of 5 solar
g masses show quasiperiodic oscillations that require impact with a
g solid surface. In other words, the data shows that these are
g neutron stars, not the black holes required by GR.

I'll certainly defer to Steve Carlip, but that is not my
understanding.

g Deference is useless. The understanding (if any) should be based
g upon the scientific method.

Understanding often also depends on the amount of time that one has
spent working on a problem.

And your understanding will not increase, unless you -- yourself -- spend
time on the problem. Understanding cannot be "borrowed" from others.

Steve has considerably more experience
working on problems in general relativity than do I. If we disagree,
it is more likely that I am in the one in error, or I defer to Steve's
experience.

To each their own. Although Steve is far more experienced in GR theory than
I am, I have found that he has made several incorrect statements in the
past. I do not, therefore, "defer" to his statements. I look at the
support for each view.

Quasi-periodic oscillations (QPOs) have been seen from accreting
white dwarfs, neutron stars, and black hole candidates. What is
*not* seen from black hole candidates are Type I X-ray bursts.
This has been interpreted (most notably by Ramesh Narayan) as
evidence that black hole candidates lack a surface, i.e., that they
have an event horizon.

g And QPO's themselves are direct, positive evidence for a solid
g surface. In short, you are arguing that lack of any reporting of
g one effect (X-ray bursts) cancels all direct observations of
g another effect. X-ray bursts are uncommon (even theoretically).
g QPOs are common.

My first two sentences are observational results, as anybody who does
a quick search of ADS can attest.

LOL! Observation of "non-observation?"

Only the first sentence are about claims to observational results. The
second is not.

The statement that QPOs are positive evidence for a solid surface is
an inference, for which you have provided no evidence.

You are correct.

g I do not accept the validity of Ramesh's logic. What is *your*
g interpretation? Can the lack of a report of one observation
g obviate a multitude of other, direct observations?

You've provided no support for your assertion that QPOs indicate a
solid surface.

I could go hunting the old references up. But are you claiming that QPOs
were *not* initially identified as the result of impact of accretion disc
material onto the surface of a white dwarf or collapsar?

--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}

greywolf42 wrote in message
...
wrote in message
...
greywolf42 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/...0e3d3753038238
"Hello? Steve? Any Relativists?"

From:
http://groups-beta.google.com/group/...deef0f9c308d3e

", 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=uk....supernews.com
http://www.google.com/groups?selm=6p...7%40nntp2.onem...
http://www.google.com/groups?selm=iz...296337%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}