The Slope Of The Rotation Curve

When I announced here that I had calculated the local slope of the Milky
Way's rotation curve from the kinematics of local stars, and found that
it was not flat, as predicted by CDM and MOND, but much closer to the
expected Newtonian curve for a mass distribution following that of
visible matter, I recall some scepticism.

I have recently redone the calculation using more accurate data from the
Hipparcos New Reduction, and a much larger population of stars for which
we have complete kinematic data. http://arxiv.org/abs/0812.4032, with
the same result.

Perhaps more interesting is that this result agrees perfectly with the
local slope calculated from HI and CO.
http://adsabs.harvard.edu/full/1991ARA&A..29..195C

A short summary, with diagrams and links to papers, and mention of the
issues this creates for both CDM and MOND is given at
http://www.teleconnection.info/rqg/SlopeOfRotationCurve

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

I think we discussed this already in an earlier thread a while ago, but I
would nevertheless like to bring this up again:

the flat rotation curves are almost exclusively obtained by measurements of
gas velocities rather than stellar velocities. The point is that during
phases of ionization, gas atoms are practically only subject to
electromagnetic forces, so they will for instance be trapped (and dragged
along) by moving magnetic field lines. Even after recombination, the gas
will then maintain the tangential velocities imparted via the magnetic field
from inner regions of the galaxy (see my web page
http://www.physicsmyths.org.uk/darkmatter.htm for more).

So it would not surprise me if actual stellar velocity curves differ from
this (and indeed follow more closely a Newtonian rotation curve for the
observed mass distribution).


By the way, I do not see that the data represented in the reference could
confirm (or contradict) your result in any way. If you look at Fig.3 in that
paper (
http://articles.adsabs.harvard.edu//...00206.000.html )
, then you can see that beyond 8 kpc, the error bars for the data are so
huge as to render the results practically worthless, whereas between 4-8
kpc, the data seem to be affected by systematic errors as the scatter of the
data is much larger than should be allowed by the size of the error bars.
Indeed, if you ignore the data points near 6kpc as outliers, the velocity
looks pretty much constant to me between 4-8 kpc. This would then again show
stellar velocity curves are different from gas velocity curves (although as
I said, the data presented in this reference are not really conclusive
anyway).

Thomas

Thus spake Thomas Smid
I think we discussed this already in an earlier thread a while ago, but I
would nevertheless like to bring this up again:

the flat rotation curves are almost exclusively obtained by measurements of
gas velocities rather than stellar velocities. The point is that during
phases of ionization, gas atoms are practically only subject to
electromagnetic forces, so they will for instance be trapped (and dragged
along) by moving magnetic field lines. Even after recombination, the gas
will then maintain the tangential velocities imparted via the magnetic field
from inner regions of the galaxy (see my web page
http://www.physicsmyths.org.uk/darkmatter.htm for more).

Readers will know that this process is complete fantasy. Rotation curves
are calculated from neutral gas.

By the way, I do not see that the data represented in the reference could
confirm (or contradict) your result in any way. If you look at Fig.3 in that
paper (
http://articles.adsabs.harvard.edu//.....195C/0000206.
000.html )

You may not have noticed that this is actually the diagram which I
reproduce on the website.

, then you can see that beyond 8 kpc, the error bars for the data are so
huge as to render the results practically worthless, whereas between 4-8
kpc, the data seem to be affected by systematic errors as the scatter of the
data is much larger than should be allowed by the size of the error bars.
Indeed, if you ignore the data points near 6kpc as outliers, the velocity
looks pretty much constant to me between 4-8 kpc. This would then again show
stellar velocity curves are different from gas velocity curves (although as
I said, the data presented in this reference are not really conclusive
anyway).

There are enough good points in the data up to about R0 = 10 kpc, and
agreement between curves from two different researchers. Of course, if
you ignore data you can get any curve you want. There is no reason that
curves of neutral gas and stars should be very different.


Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

"Oh No" wrote in message
...
Thus spake Thomas Smid
I think we discussed this already in an earlier thread a while ago, but I
would nevertheless like to bring this up again:

the flat rotation curves are almost exclusively obtained by measurements
of
gas velocities rather than stellar velocities. The point is that during
phases of ionization, gas atoms are practically only subject to
electromagnetic forces, so they will for instance be trapped (and dragged
along) by moving magnetic field lines. Even after recombination, the gas
will then maintain the tangential velocities imparted via the magnetic
field
from inner regions of the galaxy (see my web page
http://www.physicsmyths.org.uk/darkmatter.htm for more).

Readers will know that this process is complete fantasy. Rotation curves
are calculated from neutral gas.

First of all, most readers will actually assume that rotation curves are
obtained by measuring the velocity of stars. So it is indeed important to
point out that in the vast majority of cases they are obtained by measuring
the velocity of interstellar gas.

It is also true that neutral gas atoms are being measured, but the point is
that each atom becomes ionized every now and then (either due to background
radiation or because of 'auto-ionization' (as suggested on my page
http://www.plasmaphysics.org.uk/#auto ), and during this phase,
electromagnetic fields will obviously affect the dynamics of the particles.
Now even if an ion subsequently recombines with an electron, it will
maintain the velocity imparted by the electromagnetic field (with the change
in kinetic energy being due to the work done by the electromagnetic field).

So in a closed system, if you just wait long enough, eventually all the
neutral atoms will be affected by electromagnetic fields.

As an example, consider a permanent magnet that you move past a stationary
neutral atom. As long as the atom stays neutral, it will be unaffected, but
if the atom suddenly becomes ionized, it will be trapped by the magnetic
field lines and be dragged along by the magnet. If then the ion and electron
eventually recombine, they will continue to move on with the velocity of the
magnet even though they are not trapped by the field lines anymore.

Assume now a rotating rather than linearly moving magnet, and you are almost
there.

By the way, I do not see that the data represented in the reference could
confirm (or contradict) your result in any way. If you look at Fig.3 in
that
paper (
http://articles.adsabs.harvard.edu//.....195C/0000206.
000.html )

You may not have noticed that this is actually the diagram which I
reproduce on the website.

, then you can see that beyond 8 kpc, the error bars for the data are so
huge as to render the results practically worthless, whereas between 4-8
kpc, the data seem to be affected by systematic errors as the scatter of
the
data is much larger than should be allowed by the size of the error bars.
Indeed, if you ignore the data points near 6kpc as outliers, the velocity
looks pretty much constant to me between 4-8 kpc. This would then again
show
stellar velocity curves are different from gas velocity curves (although
as
I said, the data presented in this reference are not really conclusive
anyway).

There are enough good points in the data up to about R0 = 10 kpc, and
agreement between curves from two different researchers. Of course, if
you ignore data you can get any curve you want. There is no reason that
curves of neutral gas and stars should be very different.

You may want to have a closer look at the diagram again:

between 4 - 8 kpc, I count about roughly 50 data points. The error bars of
more than half of those miss the 'best-fit' curve altogether by up to 5
standard deviations or more. Such a situation is completely unacceptable. It
wouldn't even be fit for passing a school project, let alone for a
scientific publication..

Thomas

Thus spake Thomas Smid
"Oh No" wrote in message
...
Thus spake Thomas Smid
I think we discussed this already in an earlier thread a while ago, but I
would nevertheless like to bring this up again:

the flat rotation curves are almost exclusively obtained by measurements
of
gas velocities rather than stellar velocities. The point is that during
phases of ionization, gas atoms are practically only subject to
electromagnetic forces, so they will for instance be trapped (and dragged
along) by moving magnetic field lines. Even after recombination, the gas
will then maintain the tangential velocities imparted via the magnetic
field
from inner regions of the galaxy (see my web page
http://www.physicsmyths.org.uk/darkmatter.htm for more).

Readers will know that this process is complete fantasy. Rotation curves
are calculated from neutral gas.

First of all, most readers will actually assume that rotation curves are
obtained by measuring the velocity of stars. So it is indeed important to
point out that in the vast majority of cases they are obtained by measuring
the velocity of interstellar gas.

It is also true that neutral gas atoms are being measured, but the point is
that each atom becomes ionized every now and then (either due to background
radiation or because of 'auto-ionization' (as suggested on my page
http://www.plasmaphysics.org.uk/#auto ), and during this phase,
electromagnetic fields will obviously affect the dynamics of the particles.
Now even if an ion subsequently recombines with an electron, it will
maintain the velocity imparted by the electromagnetic field (with the change
in kinetic energy being due to the work done by the electromagnetic field).

Atoms of hydrogen do not become spontaneously ionised every now and
again.


There are enough good points in the data up to about R0 = 10 kpc, and
agreement between curves from two different researchers. Of course, if
you ignore data you can get any curve you want. There is no reason that
curves of neutral gas and stars should be very different.

You may want to have a closer look at the diagram again:

between 4 - 8 kpc, I count about roughly 50 data points.

Ok, I took a closer look. But did you? There are about 100 data points
in this range.

The error bars of
more than half of those miss the 'best-fit' curve altogether by up to 5
standard deviations or more. Such a situation is completely unacceptable. It
wouldn't even be fit for passing a school project, let alone for a
scientific publication..

In fact it has been considered fit for scientific publication. The error
bars concern measurement errors. It is to be expected that there will
also be a real distribution of velocities about the best fit curve, and
that the motions of gas will be different in and between spiral arms.
Your objections would not be fit for a pass in a school project.

[Mod. note: enough about school projects, please -- mjh]

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

"Oh No" wrote in message
...
Thus spake Thomas Smid
"Oh No" wrote in message
...
Thus spake Thomas Smid
I think we discussed this already in an earlier thread a while ago, but
I
would nevertheless like to bring this up again:

the flat rotation curves are almost exclusively obtained by measurements
of
gas velocities rather than stellar velocities. The point is that during
phases of ionization, gas atoms are practically only subject to
electromagnetic forces, so they will for instance be trapped (and
dragged
along) by moving magnetic field lines. Even after recombination, the gas
will then maintain the tangential velocities imparted via the magnetic
field
from inner regions of the galaxy (see my web page
http://www.physicsmyths.org.uk/darkmatter.htm for more).

Readers will know that this process is complete fantasy. Rotation curves
are calculated from neutral gas.

First of all, most readers will actually assume that rotation curves are
obtained by measuring the velocity of stars. So it is indeed important to
point out that in the vast majority of cases they are obtained by
measuring
the velocity of interstellar gas.

It is also true that neutral gas atoms are being measured, but the point
is
that each atom becomes ionized every now and then (either due to
background
radiation or because of 'auto-ionization' (as suggested on my page
http://www.plasmaphysics.org.uk/#auto ), and during this phase,
electromagnetic fields will obviously affect the dynamics of the
particles.
Now even if an ion subsequently recombines with an electron, it will
maintain the velocity imparted by the electromagnetic field (with the
change
in kinetic energy being due to the work done by the electromagnetic
field).

Atoms of hydrogen do not become spontaneously ionised every now and
again.

I didn't say that atoms become spontaneously ionised. They become ionized
due to background radiation and particle collisions. And this will
inevitably happen to any atom. It is just a question of time (according to
my estimate it could be on a time scale comparable to the galactic rotation
time, but it is difficult to say with certainty as the physical conditions
in interstellar space are not very well known in this respect).



There are enough good points in the data up to about R0 = 10 kpc, and
agreement between curves from two different researchers. Of course, if
you ignore data you can get any curve you want. There is no reason that
curves of neutral gas and stars should be very different.

You may want to have a closer look at the diagram again:

between 4 - 8 kpc, I count about roughly 50 data points.

Ok, I took a closer look. But did you? There are about 100 data points
in this range.

The error bars of
more than half of those miss the 'best-fit' curve altogether by up to 5
standard deviations or more. Such a situation is completely unacceptable.
It
wouldn't even be fit for passing a school project, let alone for a
scientific publication..

In fact it has been considered fit for scientific publication.

It has been passed without being fit. I would not have passed it for the
reasons mentioned.

The error
bars concern measurement errors. It is to be expected that there will
also be a real distribution of velocities about the best fit curve, and
that the motions of gas will be different in and between spiral arms.

Yes, so? This implies then that the 'best-fit' curve does not have a high
enough order to correctly represent the data. So with what justification are
you comparing your own data to such an insufficient (and lastly meaningless)
curve?

Thomas

Thus spake Thomas Smid
The error
bars concern measurement errors. It is to be expected that there will
also be a real distribution of velocities about the best fit curve, and
that the motions of gas will be different in and between spiral arms.

Yes, so? This implies then that the 'best-fit' curve does not have a
high enough order to correctly represent the data.

Simply false.

So with what justification are you comparing your own data to such an
insufficient (and lastly meaningless) curve?



Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex