Perihelion shift of S2

S2 is the closest star to the supermassive black hole
Sgr A* at the center of the Milky Way and has a
highly elliptical orbit. Will relativistic effects cause
precession of the perihelion of S2 that can be accurately
predicted? Is there any chance of dark matter
having any effect at such small distances?

Ed Keane III wrote:

S2 is the closest star to the supermassive black hole
Sgr A* at the center of the Milky Way and has a
highly elliptical orbit. Will relativistic effects cause
precession of the perihelion of S2 that can be accurately
predicted? Is there any chance of dark matter
having any effect at such small distances?


So far we have not much more than one orbit of data.
http://www.mpe.mpg.de/www_ir/ir_recent.php

"Sam Wormley" wrote in message
...
Ed Keane III wrote:

S2 is the closest star to the supermassive black hole
Sgr A* at the center of the Milky Way and has a
highly elliptical orbit. Will relativistic effects cause
precession of the perihelion of S2 that can be accurately
predicted? Is there any chance of dark matter
having any effect at such small distances?


So far we have not much more than one orbit of data.
http://www.mpe.mpg.de/www_ir/ir_recent.php

It has been observed since 1992 and has a 15.2 year
period. If there is a chance that dark matter is not the
reason for anomalies in orbital motion in the outer regions
of galaxies then one (I) might be curious if everything is
moving as expected at the core. Do we know enough
about mass distribution in this area to make such predictions?

http://www.solstation.com/x-objects/s2orb-b.jpg

Ed Keane III wrote in message
. ..
S2 is the closest star to the supermassive black hole
Sgr A* at the center of the Milky Way and has a
highly elliptical orbit. Will relativistic effects cause
precession of the perihelion of S2 that can be accurately
predicted? Is there any chance of dark matter
having any effect at such small distances?

Why go so far out? We have two excellent examples close by, and have known
about them since 1977. Long before the much ballyhooed PSR1913+16.

They are DI Herculis and AS Camelopardalis.

These two are much simpler systems with none of the massive complications of
PSR1913+16 or even Mercury. No error has ever been found in the data. They
were selected because of their felicitous identification as eclipsing
binaries and spherical stars -- so there is no doubt about orbital
inclination. They were identified specifically to test GR.

But because GR's predictions are massively off observation (by factors of 2
to 4), these stars have sunk into obscurity. (Everybody 'knows' about them,
but no one talks about them.)

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"greywolf42" escribió en el mensaje
...
Ed Keane III wrote in message
. ..
S2 is the closest star to the supermassive black hole
Sgr A* at the center of the Milky Way and has a
highly elliptical orbit. Will relativistic effects cause
precession of the perihelion of S2 that can be accurately
predicted? Is there any chance of dark matter
having any effect at such small distances?

Why go so far out? We have two excellent examples close by, and have
known
about them since 1977. Long before the much ballyhooed PSR1913+16.

They are DI Herculis and AS Camelopardalis.

These two are much simpler systems with none of the massive complications
of
PSR1913+16 or even Mercury. No error has ever been found in the data.
They
were selected because of their felicitous identification as eclipsing
binaries and spherical stars -- so there is no doubt about orbital
inclination. They were identified specifically to test GR.

But because GR's predictions are massively off observation (by factors of
2
to 4), these stars have sunk into obscurity. (Everybody 'knows' about
them,
but no one talks about them.)

Uhm... just what I was looking for. Could you please give some bibliographic
(or web) references on data about them and some of those analysis "off
observation by factors of 2 to 4" ? Thanks in advance.

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

"EK" == Ed Keane writes:

EK S2 is the closest star to the supermassive black hole Sgr A* at
EK the center of the Milky Way and has a highly elliptical
EK orbit. Will relativistic effects cause precession of the
EK perihelion of S2 that can be accurately predicted?

I'm not sure. I think a larger worry would be whether its orbit will
remain stable over any substantial amount of time. There are a lot of
stars in the central cluster. Their individual gravitational tugs can
perturb the orbit of S2 to the point that it may not close for any
substantial amount of time.

EK Is there any chance of dark matter having any effect at such small
EK distances?

Well, in a sense, Sgr A* is dark matter. More properly, the
supermassive black hole, around which is a region that emits radio
radiation that we detect as the source Sgr A*, is (baryonic) dark
matter. So, yes.

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In sci.astro Cesar Sirvent wrote:

"greywolf42" escribio en el mensaje
...

[...]
Why go so far out? We have two excellent examples close by,
and have known about them since 1977. Long before the
much ballyhooed PSR1913+16.

They are DI Herculis and AS Camelopardalis.

These two are much simpler systems with none of the massive
complications of PSR1913+16 or even Mercury. No error has
ever been found in the data. They were selected because of
their felicitous identification as eclipsing binaries and spherical
stars -- so there is no doubt about orbital inclination. They
were identified specifically to test GR.

But because GR's predictions are massively off observation
(by factors of 2 to 4), these stars have sunk into obscurity.
(Everybody 'knows' about them, but no one talks about them.)

Uhm... just what I was looking for. Could you please give some
bibliographic (or web) references on data about them

The best place to start is two papers by Claret, Astron. Astrophys.
327 (1997) 11-21 and Astron. Astrophys. 330 (1998) 533-540.
The first of these analyzes ten relativistic eclipsing binaries for
which observations agree well with the GR predictions. The
second paper concentrates on DI Her, along with two other
systems, AS Cam and V541 Cyg, for which there are significant
discrepancies. One of the things that must be explained is why
there is this inconsistency, that is, why many eclipsing binaries
show the apsidal motion predicted by GR but a few do not. The
one significant difference that Claret finds is that the three cases
that show disagreements wth GR have the three longest periods
of apsidal motion.

(I should note also that the discrepancy for V541 Cyg seems to have
gone away with better measurements -- see Volkov and Khaliullin,
Information Bulletin on Variable Stars, 4680, 1.)

Steve Carlip

escribió en el mensaje
...
In sci.astro Cesar Sirvent wrote:

"greywolf42" escribio en el mensaje
...

[...]
Why go so far out? We have two excellent examples close by,
and have known about them since 1977. Long before the
much ballyhooed PSR1913+16.

They are DI Herculis and AS Camelopardalis.

These two are much simpler systems with none of the massive
complications of PSR1913+16 or even Mercury. No error has
ever been found in the data. They were selected because of
their felicitous identification as eclipsing binaries and spherical
stars -- so there is no doubt about orbital inclination. They
were identified specifically to test GR.

But because GR's predictions are massively off observation
(by factors of 2 to 4), these stars have sunk into obscurity.
(Everybody 'knows' about them, but no one talks about them.)

Uhm... just what I was looking for. Could you please give some
bibliographic (or web) references on data about them

The best place to start is two papers by Claret, Astron. Astrophys.
327 (1997) 11-21 and Astron. Astrophys. 330 (1998) 533-540.
The first of these analyzes ten relativistic eclipsing binaries for
which observations agree well with the GR predictions. The
second paper concentrates on DI Her, along with two other
systems, AS Cam and V541 Cyg, for which there are significant
discrepancies. One of the things that must be explained is why
there is this inconsistency, that is, why many eclipsing binaries
show the apsidal motion predicted by GR but a few do not. The
one significant difference that Claret finds is that the three cases
that show disagreements wth GR have the three longest periods
of apsidal motion.

(I should note also that the discrepancy for V541 Cyg seems to have
gone away with better measurements -- see Volkov and Khaliullin,
Information Bulletin on Variable Stars, 4680, 1.)

Steve Carlip

Thanks. However, I understand that for AS Cam and DI Her the disagreements
are not likely due to poor measurements, right?

wrote in message
...
In sci.astro Cesar Sirvent wrote:

"greywolf42" escribio en el mensaje
...

[...]
Why go so far out? We have two excellent examples close by,
and have known about them since 1977. Long before the
much ballyhooed PSR1913+16.

They are DI Herculis and AS Camelopardalis.

But because GR's predictions are massively off observation
(by factors of 2 to 4), these stars have sunk into obscurity.
(Everybody 'knows' about them, but no one talks about them.)

DI Herculis and AS Camelopardalis? 164 hits on Google.
That is less than no one.

Uhm... just what I was looking for. Could you please give some
bibliographic (or web) references on data about them

The best place to start is two papers by Claret, Astron. Astrophys.
327 (1997) 11-21 and Astron. Astrophys. 330 (1998) 533-540.

http://aa.springer.de/papers/7327001/2300011/small.htm
http://aa.springer.de/papers/8330002...sc3.htm#sc3.10.

And they are in english (words).

wrote in message
...
In sci.astro Cesar Sirvent wrote:

"greywolf42" escribio en el mensaje
...

[...]
Why go so far out? We have two excellent examples close by,
and have known about them since 1977. Long before the
much ballyhooed PSR1913+16.

They are DI Herculis and AS Camelopardalis.

These two are much simpler systems with none of the massive
complications of PSR1913+16 or even Mercury. No error has
ever been found in the data. They were selected because of
their felicitous identification as eclipsing binaries and spherical
stars -- so there is no doubt about orbital inclination. They
were identified specifically to test GR.

But because GR's predictions are massively off observation
(by factors of 2 to 4), these stars have sunk into obscurity.
(Everybody 'knows' about them, but no one talks about them.)

Uhm... just what I was looking for. Could you please give some
bibliographic (or web) references on data about them

A general overview is in Astronomy, Nov. 1995, p 54-59, "The Mystery of DI
Herculis".

The original cite: "The apsidal motion of the eccentric eclipsing binary DI
Herculis - an apparent discrepancy with general relativity", Guinan, E. F.;
Maloney, F. P., Astronomical Journal (ISSN 0004-6256), vol. 90, Aug. 1985,
p. 1519-1528.

http://adsabs.harvard.edu/cgi-bin/np........90.1519G&
amp;db_key=AST&high=3e5ffa223d11852

Abstract:

"The apsidal motion of the eccentric eclipsing binary DI Herculis (HD
175227) is determined from an analysis of the available observations and
eclipse timings from 1959 to 1984. Least squares solutions to the primary
and secondary minima extending over an 84-yr interval yielded a small
advance of periastron omega dot of 0.65 deg/100 yr + or - 0.18/100 yr. The
observed advance of the periastron is about one seventh of the theoretical
value of 4.27 deg/100 yr that is expected from the combined relativistic and
classical effects. The discrepancy is about -3.62 deg/100 yr, or a magnitude
of about 20 sigma. Classical mechanisms which explain the discrepancy are
discussed, together with the possibility that there may be problems with
general relativity itself."

The best place to start is two papers by Claret, Astron. Astrophys.
327 (1997) 11-21 and Astron. Astrophys. 330 (1998) 533-540.
The first of these analyzes ten relativistic eclipsing binaries for
which observations agree well with the GR predictions.

A horrible place to start. But it does defend the Faith....

Claret's primary purpose is not to test GR, but to examine the interiors of
stars, due to tidal distortions (from primarily Newtonian gravity). The
authors studiously ignore good tests of GR (eclipsing binaries that are not
tidally-distorted). In fact, they state early on:

"In the papers quoted above we have only analysed the systems for which the
relativistic contribution to the total apsidal motion were small."

In short -- GR is examined only when such effects have been reduced to noise
on a stronger signal. The only mention of the classic Di Her case is when
'dissing' a particular theory.


Keep in mind that eclipsing binaries are rare, due to simple statistics.
Stellar orbits are usually quite a bit larger than the diameters of the
component stars. The odds of a given double star system being aligned with
Earth is very low. The larger the radius of the orbit, the lower the
probability. Of the eclipsing binaries that we know, the vast majority will
unavoidably be close binaries -- because the odds of a binary being aligned
with Earth is inversely proportional to the orbital radius.

But close binaries are distorted into non-spherical shapes, due to the
gravitational potentials of close star systems. These non-spherical shapes
cannot be observed directly. But they can be inferred by a suitable theory
of gravity, due to changes in periastron position. However, if you have to
infer the shape (from GR) -- then you have no test of GR.

Guinan's purpose was explicitly to find those few, rare cases where GR could
be tested without circularity. Claret's purpose was to find all the 'muddy'
systems he could. Because he was looking at theories of stellar
interiors -- not at systems that would test GR.

The
second paper concentrates on DI Her, along with two other
systems, AS Cam and V541 Cyg, for which there are significant
discrepancies. One of the things that must be explained is why
there is this inconsistency, that is, why many eclipsing binaries
show the apsidal motion predicted by GR but a few do not.

Even Claret's conclusion is simply that DI Herculis disagrees with GR --
despite 20 years of 'intensive effort' (quote from Claret paper) to make it
behave.....



The reason is that the 'good tests' of GR (those rarer eclipsing binaries
with large orbital separations, and undistorted stars) have no adjustible
parameters. GR fails on these. But if you concentrate on distorted stars
(which you cannot observe directly) you can find a theoretical distortion to
match every case with GR.

The 'explanation' that good tests don't match GR is well known. (At least
according to the Astonomy paper, above.)

The
one significant difference that Claret finds is that the three cases
that show disagreements wth GR have the three longest periods
of apsidal motion.

Yes. Exactly as noted in the literature a decade prior to Claret. And
explained by Guinen.

1) long period equals large separation distance.
2) large separation distance equals round stars, due to lack of tidal motion
3) lack of tidal distortion eliminates any complexities and free parameters
from the problem
4) GR is disproved whenever you can't hide the discrepacy in free
parameters.

Good tests of GR disprove it. So the faithful write papers on complex
systems that can be tweaked to match GR.

(I should note also that the discrepancy for V541 Cyg seems to have
gone away with better measurements -- see Volkov and Khaliullin,
Information Bulletin on Variable Stars, 4680, 1.)

Going away just like the apsides of Venus. I'll look this up later.....

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