Mysterious gas cloud that was supposed to enter Milky Way centralblack hole turned out to be a couple of merging stars instead!

In article ,
sean writes:
Why cant a group of objects rapidly rotate around a common central
point without a black hole?

They can, but the center of the Milky Way has 4 million solar masses
within a radius of a few thousand astronomical units. If that's not
a black hole, it's something even weirder. A cluster of neutron
stars (as someone else suggested) would fit in the volume, but the
lifetime of such a cluster would be very short. Some objects would
be expelled, and orbits of the rest would decay very rapidly because
of gravitational radiation. Also, it's not obvious how such a
cluster could form in the first place. How could neutron stars have
been segregated from the rest of a stellar population?

... current theory on galaxy ... rotation speeds ...
all the disc mass in the calculation is erroneously assumed, for
expedience, to be at the center of the disc.

That's silly. Of course nobody assumes that. Perhaps some press
release used it for an illustration?

The simplest assumption is that mass follows the light distribution
(corrected from 2d to 3d), but a wide variety of other assumptions
have been tried.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On Monday, 17 November 2014 22:26:59 UTC, Steve Willner wrote:
In article ,
sean writes:
Why cant a group of objects rapidly rotate around a common central
point without a black hole?

They can, but the center of the Milky Way has 4 million solar masses
within a radius of a few thousand astronomical units. If that's not
a black hole, it's something even weirder. A cluster of neutron
stars (as someone else suggested) would fit in the volume, but the
lifetime of such a cluster would be very short. Some objects would
be expelled, and orbits of the rest would decay very rapidly because
of gravitational radiation. Also, it's not obvious how such a
cluster could form in the first place. How could neutron stars have
been segregated from the rest of a stellar population?

This is what I was disputing. How do you know the center of the milky
way is 4 million solar masses? (I assume you are referring to sagitarius A*)
My understanding is that this is only an assumption based on rotation
speeds of the observable stars like S2 etc. Maybe the understanding of
what g forces are at work in galaxy cores are incorrect. For instance we
know from rotation curves that the assumption that most of the mass of the
disc is in the core ,assuming estimates based on illumination,... is incorrect.
Obviously the mass of the galaxy is spread much more evenly across the disc
then generally assumed. Maybe assumptions about rotation speeds in the core
are also incorrect. I don't see why one couldn't have the observed
rotational speeds near the center of the core without having to factor
in a Black Hole. We have no other precedence for core behaviour so
its odd we have to assume they behave like the solar system where most of the mass *is* at the center. And one of the points I made in previous posts was
that there are galaxy centers that astrophysists agree don't have black
holes (Yousof K cited one) , yet they are essentially disc galaxies with
cores. And as we cant see the rotational speeds of those cores one cant rule
out the possibility that these non BH galaxies also have stars rotating
at faster speeds at the center. Without a central black hole.

... current theory on galaxy ... rotation speeds ...
all the disc mass in the calculation is erroneously assumed, for
expedience, to be at the center of the disc.

That's silly. Of course nobody assumes that. Perhaps some press
release used it for an illustration?
v2 = (G M)/r
You are wrong. Its a general assumption implicit in the calculations.
Look at any of the calculations for rotational speeds, G,m, and radius.
Any of these formula Ive seen assume ALL the mass at the center. If you
disagree show me the part of the calculation that spreads M across the disc.

The simplest assumption is that mass follows the light distribution
(corrected from 2d to 3d), but a wide variety of other assumptions
have been tried.
Unfortunately the simplest assumption is erroneous. One only has to
look at observed galaxy rotation curves to see this is the case.
After all which method is best for calculating mass distribution in the solar
system. Looking at the brightness of the sun , or measuring orbital
speeds of planets?

Dear sean:

On Tuesday, November 18, 2014 4:25:51 AM UTC-7, sean wrote:
....
My understanding is that this is only an assumption
based on rotation speeds of the observable stars
like S2 etc. Maybe the understanding of what g
forces are at work in galaxy cores are incorrect.

How do the stars at the core, know to have different physics?

For instance we know from rotation curves that
the assumption that most of the mass of the
disc is in the core ,assuming estimates based on
illumination,... is incorrect.

Which does not address in any way, the center where the luminance vs. total mass number is derived.

Obviously the mass of the galaxy is spread much
more evenly across the disc then generally assumed.

Just not near the center, where the calibration curve is derived.

Maybe assumptions about rotation speeds in the core
are also incorrect. I don't see why one couldn't
have the observed rotational speeds near the center
of the core without having to factor in a Black
Hole.

You have been provided evidence, and chosen to ignore.

The central objects are orbiting a mass of 4 million solar equivalents. The mass is dense, within 980 AU radius. It is centrally located, since the orbits are not chaotic. It does not shred a cloud, so is *very* dense, and does not change position for the duration of the cloud's passing.

Ignore away...

David A. Smith

David wrote...
On Tuesday, November 18, 2014 4:25:51 AM UTC-7, sean wrote: ...
My understanding is that this is only an assumption
based on rotation speeds of the observable stars
like S2 etc. Maybe the understanding of what g
forces are at work in galaxy cores are incorrect.

How do the stars at the core, know to have different physics?

For instance we know from rotation curves that
the assumption that most of the mass of the
disc is in the core ,assuming estimates based on
illumination,... is incorrect.

Which does not address in any way, the center where the luminance vs. total mass number is derived.

Obviously the mass of the galaxy is spread much
more evenly across the disc then generally assumed.

Just not near the center, where the calibrationcurveisderived.

Maybe assumptions about rotation speeds in the core
are also incorrect. I don't see why one couldn't
have the observed rotational speeds near the center
of the core without having to factor in a Black
Hole.

you have been provided evidence, and chosen to ignore.

You have provided no evidence that says that all cores
have to have black holes. Or evidence that rules out faster
orbitting stars at the center of cores can only occur with
associated central black holes.

the central objects are orbiting a mass of 4 million solar equivalents.
The mass is dense, within 980 AU radius. It is centrally located, since
the orbits are not chaotic. It does not shred a cloud, so is *very* dense,
and does not change position for the duration of the cloud's passing.

The 4 million mass is an assumption based on the observation that when the
mass is mostly in the center, Then objects have higher orbital speeds.But all
cores appear to have orbitting stellar mass fairly evenly spread. These cores
are systems that have no other precedence to compare to. Theres no physics
that says an evenly spread halo of stars orbitting a central axis has to have a
black hole at its center. In fact Yousof K just confirmed there is at least one
example that for other reasons cant have a black hole. And yet it has a disc
and a central core of orbitting stars

Ignore away...

Sorry David but you must stick to observed data only and not make
claims that have no supporting evidence. For example...
Show me the evidence that the example cited by Yousof doesnt have
stars orbitting at very fast speeds at its center.You cant, because
there isnt any. So its you who ignores the evidence, or more to the point,
the lack of it. Not to mention the fact that the supposed gas cloud wasnt
torn apart by any black hole as erroneously predicted. And the fact
that the supposed twin star system that was at one time supposed
to be a gas cloud, hasnt actually been observed. Only assumed,
because the previous prediction failed. So the assumption that the cloud
that wasnt torn apart couldnt be a cloud because clouds cant orbit
core centers at those speeds...is a false assumption ..because there is
no evidence or precedence to say that gas clouds or stars orbitting core
centers at higher speeds cannot do so without a central black hole.
If you think there is evidence ... Dont just say you have evidence,
Show me the evidence.

On 11/19/14 05:30, sean wrote:
If you think there is evidence ... Dont just say you have evidence,
Show me the evidence.

Here's the evidence.

Infrared observations of Sagittarius A* (the bright radio source at the
center of the Milky Way) show at least half a dozen stars in fairly
tight orbits. One of them, S2, has been observed for more than one
revolution. We know its orbital period (15.56 +/- 0.35 yr) to about 2%.
We know the size of its orbit on the sky (0.1203 +/- 0.0027 arcsec) to
about 2%. We know the distance (25900 +/- 1400 light years, or 7940
+/- 420 parsecs) to about 5%.

The period and size of an orbit are related by Kepler's Third Law, which
in its simplest form is
G M = a^3 n^2
with G the gravitational constant, M the system mass, a the semimajor
axis, and n the mean motion (angular motion in radians per unit time, or
2 pi divided by the period).

Let's do the math. The numbers below are from Wikipedia's article on
S2, http://en.wikipedia.org/wiki/S2_%28star%29

n = 2 pi / (15.56 yr * 31557600 sec/yr) = 1.280e-8 radians/sec
a = 0.1203 arcsec * 7940 parsec * 149597870700 m/AU = 1.429e14 meters
G = 6.674e-11 m^3 / (kg s^2)

M = a^3 n^2 / G = 7.158e36 kg

One solar mass is 1.989e30 kg, so I get M = 3.6e6 solar masses, with an
uncertainty of about 15% (dominated by the 5% uncertainty in distance).
Wikipedia's article on Sgr A* says 2.6e6 solar masses. Either way,
we're talking about several MILLION solar masses. The angular diameter
of Sgr A* has been measured to be about 37 microarcseconds, which
translates into 0.29 AU or 44 million km.

How do you fit a few million solar masses into a volume smaller than a
sphere the size of Mercury's orbit? The density has to be on the order
0f 20 tons per cubic meter. Given what we know about atomic and nuclear
physics, there is no way that much matter in a volume that small can be
stable against gravitational collapse.

-- Bill Owen

On Wednesday, 19 November 2014 21:01:02 UTC, Bill Owen wrote:
On 11/19/14 05:30, sean wrote:
If you think there is evidence ... Dont just say you have evidence,
Show me the evidence.

Here's the evidence.

Infrared observations of Sagittarius A* (the bright radio source at the
center of the Milky Way) show at least half a dozen stars in fairly
tight orbits. One of them, S2, has been observed for more than one
revolution. We know its orbital period (15.56 +/- 0.35 yr) to about 2%.
We know the size of its orbit on the sky (0.1203 +/- 0.0027 arcsec) to
about 2%. We know the distance (25900 +/- 1400 light years, or 7940
+/- 420 parsecs) to about 5%.

The period and size of an orbit are related by Kepler's Third Law, which
in its simplest form is
G M = a^3 n^2
with G the gravitational constant, M the system mass, a the semimajor
axis, and n the mean motion (angular motion in radians per unit time, or
2 pi divided by the period).

Let's do the math. The numbers below are from Wikipedia's article on
S2, http://en.wikipedia.org/wiki/S2_%28star%29

n = 2 pi / (15.56 yr * 31557600 sec/yr) = 1.280e-8 radians/sec
a = 0.1203 arcsec * 7940 parsec * 149597870700 m/AU = 1.429e14 meters
G = 6.674e-11 m^3 / (kg s^2)

M = a^3 n^2 / G = 7.158e36 kg

One solar mass is 1.989e30 kg, so I get M = 3.6e6 solar masses, with an
uncertainty of about 15% (dominated by the 5% uncertainty in distance).
Wikipedia's article on Sgr A* says 2.6e6 solar masses. Either way,
we're talking about several MILLION solar masses. The angular diameter
of Sgr A* has been measured to be about 37 microarcseconds, which
translates into 0.29 AU or 44 million km.

How do you fit a few million solar masses into a volume smaller than a
sphere the size of Mercury's orbit? The density has to be on the order
0f 20 tons per cubic meter. Given what we know about atomic and nuclear
physics, there is no way that much matter in a volume that small can be
stable against gravitational collapse.
I appreciate that you've gone to a lot of effort to do some calculations.
But, you ignore a simple fact about the core. It isn't disc shape and
all the visible mass is distributed fairly evenly across the core. Unlike
the solar system where the mass *is* concentrated at the center. So its OK
for.. G M = a^3 n^2 ...to be used for the solar system. But unfortunately
that formula isn't applicable to any core of any galaxy because the mass
is distributed across any galaxy core evenly. Your use of this formula
here is erroneous. Thus..You still have no evidence.
A good example of how this type of formula is a not applicable for galaxies
disc or cores,.. is the use of it to calculate galaxy rotation curves. The
calculated orbital speeds of stars around the disc using these formulas do
NOT correctly match those observed. Why? Because the mass of the galaxy
is not concentrated at the core , but rather, spread fairly evenly across
the disc.
Besides using the wrong formula to calculate the erroneously assumed
4 million solar mass at the center of our core, you also ignore the fact
that some disc galaxies with cores,like ours, are accepted to not have black
holes. So its possible for any core of any disc galaxy, including ours,
to not have a black hole. And finally seeing as you like wiki,... if you
go to the wiki page on sagitarius A* you`ll find that it says that it is
actually possible using different mass configurations that one can calculate and
match the observed orbital speeds of the stars like S2 *without* invoking a
black hole. In other words, dont use... G M = a^3 n^2. As Ive said, that or
any similar formula, implicitly needs all or almost all of the mass to be at
the center. And its obvious from looking at any core of any galaxy that the
visible mass is not all at the core. Its spread out throughout the core.

On 11/20/14 04:18, sean wrote:
On Wednesday, 19 November 2014 21:01:02 UTC, Bill Owen wrote:
On 11/19/14 05:30, sean wrote:
If you think there is evidence ... Dont just say you have evidence,
Show me the evidence.

Here's the evidence.

Infrared observations of Sagittarius A* (the bright radio source at the
center of the Milky Way) show at least half a dozen stars in fairly
tight orbits. One of them, S2, has been observed for more than one
revolution. We know its orbital period (15.56 +/- 0.35 yr) to about 2%.
We know the size of its orbit on the sky (0.1203 +/- 0.0027 arcsec) to
about 2%. We know the distance (25900 +/- 1400 light years, or 7940
+/- 420 parsecs) to about 5%.

The period and size of an orbit are related by Kepler's Third Law, which
in its simplest form is
G M = a^3 n^2
with G the gravitational constant, M the system mass, a the semimajor
axis, and n the mean motion (angular motion in radians per unit time, or
2 pi divided by the period).

Let's do the math. The numbers below are from Wikipedia's article on
S2, http://en.wikipedia.org/wiki/S2_%28star%29

n = 2 pi / (15.56 yr * 31557600 sec/yr) = 1.280e-8 radians/sec
a = 0.1203 arcsec * 7940 parsec * 149597870700 m/AU = 1.429e14 meters
G = 6.674e-11 m^3 / (kg s^2)

M = a^3 n^2 / G = 7.158e36 kg

One solar mass is 1.989e30 kg, so I get M = 3.6e6 solar masses, with an
uncertainty of about 15% (dominated by the 5% uncertainty in distance).
Wikipedia's article on Sgr A* says 2.6e6 solar masses. Either way,
we're talking about several MILLION solar masses. The angular diameter
of Sgr A* has been measured to be about 37 microarcseconds, which
translates into 0.29 AU or 44 million km.

How do you fit a few million solar masses into a volume smaller than a
sphere the size of Mercury's orbit? The density has to be on the order
0f 20 tons per cubic meter. Given what we know about atomic and nuclear
physics, there is no way that much matter in a volume that small can be
stable against gravitational collapse.
I appreciate that you've gone to a lot of effort to do some calculations.
But, you ignore a simple fact about the core. It isn't disc shape and
all the visible mass is distributed fairly evenly across the core. Unlike
the solar system where the mass *is* concentrated at the center. So its OK
for.. G M = a^3 n^2 ...to be used for the solar system. But unfortunately
that formula isn't applicable to any core of any galaxy because the mass
is distributed across any galaxy core evenly. Your use of this formula
here is erroneous. Thus..You still have no evidence.
A good example of how this type of formula is a not applicable for galaxies
disc or cores,.. is the use of it to calculate galaxy rotation curves. The
calculated orbital speeds of stars around the disc using these formulas do
NOT correctly match those observed. Why? Because the mass of the galaxy
is not concentrated at the core , but rather, spread fairly evenly across
the disc.
Besides using the wrong formula to calculate the erroneously assumed
4 million solar mass at the center of our core, you also ignore the fact
that some disc galaxies with cores,like ours, are accepted to not have black
holes. So its possible for any core of any disc galaxy, including ours,
to not have a black hole. And finally seeing as you like wiki,... if you
go to the wiki page on sagitarius A* you`ll find that it says that it is
actually possible using different mass configurations that one can calculate and
match the observed orbital speeds of the stars like S2 *without* invoking a
black hole. In other words, dont use... G M = a^3 n^2. As Ive said, that or
any similar formula, implicitly needs all or almost all of the mass to be at
the center. And its obvious from looking at any core of any galaxy that the
visible mass is not all at the core. Its spread out throughout the core.

Thanks for your reply. I "like" Wikipedia but I acknowledge that it's
not 100% reliable. I didn't have time to dig up the real literature
references for the numbers given there.

Kepler's Third Law applies as long as the central mass is spherically
symmetric and contained entirely within the orbit. (Newton basically
invented -- or co-invented -- integral calculus in order to prove that
the gravity field of a sphere is the same as that of a point mass.)

Similarly, any spherically symmetric distribution of matter *outside*
the orbit has no effect on the orbit.

If the mass were "distributed evenly" as you assert, there would be no
net gravitational force, and stars near the center would move in
straight lines. That is not what is observed.

If the central body is not spherical, you can use spherical harmonics to
expand the gravitational potential, and the result is that the orbit
basically maintains its size, shape and period, but the orientation
changes with time. (Newton realized this too, and the details of the
moon's orbit literally gave him headaches.)

In any case, S2 and the other stars make hairpin turns when they're
close to Sgr A*, and that bespeaks a humongous acceleration, which
requires a humongous mass. There's no escaping that conclusion. One
can quibble about the details of the dynamics, but the kinematics
requires *something extremely massive*, on the order of a few million
solar masses.

Oh, and we're not talking about other galaxies, which may or may not
contain central black holes. We're talking about one specific galaxy --
our own -- in which we can detect individual stars moving rapidly, and
being accelerated dramatically -- by a huge mass. Whether that huge
mass is a black hole or something else is a different question; the fact
that there *is* a huge mass is certain.

-- Bill

On 14/11/2014 7:23 PM, John wrote:
On Fri, 14 Nov 2014 15:21:14 -0500, Yousuf Khan
wrote:

On 14/11/2014 6:22 AM, sean wrote:
On Thursday, November 13, 2014 4:55:01 PM UTC, dlzc wrote:
Dear sean:

On Thursday, November 13, 2014 7:29:49 AM UTC-7, sean wrote:


I dont see any science that says this is impossible.

No star, or collections of stars, that massive, can be that small.

Its not clear what you refer to here. What is too small?

He's referring to the central blackhole of course. The level of
concentrated mass at this point cannot be replicated by a large
collection of huge stars in that small amount of space. The central
blackhole has a mass of 4 million solar masses, and has a radius of only
17 solar radii.

You could fit quite a few neutron stars into that volume. They would
be whizzing about like demented hornets but they could exist in some
sort of semi-chaotic Galactic Cluster style mass orbit.
You could fit in even more were most of them temporary residents,
probability neutron stars.
White dwarves would probably be too bloated.

Yes, you could fit quite a few neutron stars into that space, but could
you fit 2 to 3 *million* neutron stars in there? At a typical neutron
star mass of 1.5 to 2.0 solar masses, and this region estimated to weigh
around 4 million solar masses, that's how many neutron stars you'd need
to match this weight.

With such massive individual pieces such as neutron stars, in such close
proximity, then gravity starts to become frictional due to relativistic
frame dragging, and the neutron stars will start to spiral into each
other, thus creating blackholes all over again. And those that don't get
pulled in would start to get booted out of the system. You'd have 100's
of thousands of neutron stars being ejected out of the galaxy at high
speed, leaving from the vicinity of the galactic center. We've seen a
few high velocity stars coming from there, but I'm not sure about
neutron stars, and certainly not hundreds of thousands of them.

I've seen videos of the stars at the MW Core and they don't seem to
be in ordered orbits, more like the swarming of GC's. Of course those
videos only cover a small region close to the central "object"
whatever it may be and only cover a small era of time so my impression
could be wildly wrong.

I'm not talking about the type of order that our planets have around the
Sun, with circular orbits. I'm talking about the type of orbits that the
comets around our Sun have, with elliptical orbits. The stars around
this central object have that same comet-like order.

Without the central mass there to anchor things, the orbits of several
thousand objects around each other could not even be called elliptical.
You'd have twisted dances with 3 or 4 partners around each other, and
the orbits wouldn't trace simple shapes that repeated over and over
again. With a blackhole there, everything is swinging around the
blackhole, and it is their main dance partner.

Yousuf Khan

In article ,
sean writes:
How do you know the center of the milky
way is 4 million solar masses?

See Bill Owen's post. Observed size and period of an orbit define
the mass _interior_ to that orbit. That's how, for example, the
masses of planets in the solar system are known: from the orbits of
their satellites (natural or artificial).

all the disc mass in the calculation is erroneously assumed, for
expedience, to be at the center of the disc.
....
Its a general assumption implicit in the calculations.
... If you
disagree show me the part of the calculation that spreads M across the disc.

The first four papers I ran across in a quick search are linked he
http://adsabs.harvard.edu/abs/2014MNRAS.443..791E
http://adsabs.harvard.edu/abs/2014MNRAS.443....2E
http://adsabs.harvard.edu/abs/2013PASJ...65..118S
http://adsabs.harvard.edu/abs/2013AJ....146..121H

There are probably hundreds more in the literature. I doubt there's
even a single rotation-curve paper that treats galaxy mass as a
central point.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On 15/11/2014 10:23 AM, sean wrote:
On Friday, 14 November 2014 20:21:11 UTC, Yousuf Khan wrote:
Galaxies and globular clusters are examples. Some globular clusters have
no central blackhole, therefore their individual component stars swarm
around a common center of mass, like a swarm of bees. Not quite chaotic,
but not smooth ellipses or circles either, more like twisted rubber-band
ellipses and what not. Then there are other globular clusters which do
have a central blackhole, and they have more ordered orbitals from their
stars.

Can wee *all* the stars in our core, not just those near the center like S2?
And the same for other galaxies, can we see any of the stars at their cores to
track their paths? Also, whether for ours or another galaxy,The outer stars
must go a lot slower than the center stars. I would have thought it would be
difficult to extrapolate a rubber band orbit when you only have a
tiny fraction of its path recorded. Whether for our galaxy or another. So it
must be only an assumption, regarding the supposed rubber band paths.

We can resolve individual stars out to several million light years, at
least all of the galaxies in our Local Group galactic cluster, including
Andromeda and Triangulum galaxies. For years, we couldn't see to the
center of the Milky Way, but that had nothing to do with resolution: it
was due to dust blocking our view to the center. However, that was all
resolved with radio, infrared, x-ray, and other non-visible light
astronomy. The motions of the stars at the center of the MW are all
probably infrared images.

Addendum: just as I spoke, looks like there is a candidate galaxy that
may not have any examples of galaxies without central blackholes, that
are nearby, it looks like I was wrong. We have M33, the Triangulum
galaxy, which is part of our Local Group of galaxies, may not have a
central blackhole. Anyway, it doesn't look like they've been able to do
an exhaustive study of the motion of its central stars yet.

M33: A Galaxy with No Supermassive Black Hole - Abstract - The
Astronomical Journal - IOPscience
http://iopscience.iop.org/1538-3881/122/5/2469/
I just had a quick look at this . It seems that even for close galaxies
like this one, they are not tracking orbit paths. Rather velocity profiles
only, using spectra. So I can only conclude that we don't have examples of
orbit paths of other galaxy cores to come to the conclusion that
their orbits are irregular rather than elliptical.

Well, they don't know if Triagulum has any central blackhole in it at
all. The best guess they have is that if there is a central blackhole,
it will be from 0-3000 solar masses. Which is an incredibly small
central blackhole, you can't even call it a supermassive blackhole it's
too small, it's bigger than a stellar blackhole, so it's intermediate
sized at best. Even smaller in relation to the mass of the Triangulum
galaxy than the Milky Way's blackhole, which is also a lightweight
supermassive blackhole, but being over a 1 million solar masses, it is
definitely in the supermassive category. Andromeda's central blackhole
is thought to be 10 million solar masses for comparison. The biggest
supermassives in the universe are all over 1 billion solar masses.

For starters I personally dont agree with the theoretical concept of a BH and
correctly predicted that there would be no fireworks.


It was a 50:50 guess and you know it. Whether or not there were
fireworks has nothing to do with what's at the center of the galaxy.
What's at the center of the galaxy is pretty well known, it was this
object G2 that was mysterious.

For me it was a 100 % certainty that there would be no fireworks. Ive seen
too much evidence in all sorts of related experiments and observations
to be absolutely certain that the theoretical basis for Black Holes (including
relativity)is questionable. Hence I knew that the cloud, or whatever it may
turn out to be, would not be torn apart. In fact Im sure I predicted exactly
this prior to the no show of fireworks. The problem is that google groups no
longer offers me an obvious way to look back at all my posts over the last years
to find the relavent passage

Well, you're going to have to produce equations that say why Relativity
is wrong here then. It doesn't matter if you can't find your historical
archives of your previous discussions, if you got an equation that
proves Relativity wrong, then you don't need the history. The equations
are self-contained, and produce their own context.

calculation is erroneously assumed, for expedience, to be at the center of the disc.
Spread the mass more evenly around the disc and you get a model that does
match the observed rotation curves.

Again, galaxy rotation curves don't affect what's at the center of the
galaxy. Whether the rotation curves matched Newtonian gravity or not,
you would still need a blackhole at the center of the galaxy to anchor it.

I was just suggesting that if the disc can rotate around a central axis even
when most of the mass is outside the disc, then thats a good precedence
for assuming the core can do the same without a central black hole.
Kind of like a comparitive analogy. (water waves have similar properties
to other waves like emr)Anyways didn't you just admit that its possible to
have a core without a BH?

Most theories suggest that the central blackhole, even though it's tiny
compared to the galaxy in which it resides (usually less than 1/1000'th
the mass), it does play an important role in anchoring the position of
the galaxy and where it will reside. Much like a grain of dust anchors
where a snowflake will form in the clouds.

Yousuf Khan