Galaxies without dark matter halos?

Joseph Lazio wrote in message ...

This post has been redirected from sci.physics.research and
sci.astro.research, because the 'moderator' will not allow me to reply
there. (More on that funny aside, later.) My replies were originally
submitted on the 1st.

"TS" == Thomas Smid writes:

TS It has never been the case that all galaxies show evidence for
TS dark matter halos (...).

While true, I think it is still the case that the number of galaxies
requiring dark matter to explain their rotation curves vastly
outnumbers those that do not.

The fact of existence of a significant number of galaxies without dark
matter halos (even if a nominal minority) would add another layer of 'ad
hoc' to the dark matter 'ad hoc' postulate. For there is no reason to
believe that dark matter should "avoid" some galaxies while "swarming"
others. Hence, we must 'ad hoc' allocate dark matter to those galaxies that
'need' it, and 'ad hoc' remove dark matter from those that don't.

There is no way to 'disprove' the 'dark matter' postulate if you get to add
it when you need it, and remove it when you don't. It becomes a classic
'non-refutable' proposition. Hence, not scientific.

TS The point is that the observed anomalous rotation curves of
TS galaxies are practically always based on gas velocities which can
TS be very different from the velocities of stars (...).

It would be interesting to see some evidence to back this up.

The 'evidence' both trivial and well-known. Gas velocities are affected by
electric and magnetic fields quite easily. Stars are not. Galactic
electric and magnetic fields are not only known and measured. The spiral
rotation curves match the EM-predicted curves. No dark matter needed.

What is odd is that there is so much investment in the 'popular' assumption
that stars are just like gas, and that galactic motions are driven solely by
gravity.

In the
outer reaches of galaxies, rotation curves are based on gas velocities
because there are no (or so few) stars from which to obtain stellar
velocities. However, I think it is the case that within the optical
disk, gas and stellar velocities match fairly well.

You have no basis for this claim. There is not a single paper (to my
knowledge) for galactic rotation curves that does not depend on gas
velocities or O and B stars. The O and B stars by necessity retain the
initial velocities of the gas clouds which created them (as they are too
young to deviate significantly from same).

Moreover, as a counter-argument I'll point out the case of the
Galactic center (i.e., center of the Milky Way Galaxy). For many
years, people measured gas velocities that seemed to indicate a large
dark mass (i.e., a supermassive black hole). A key uncertainty was
whether the gas velocities were being affected by non-gravitational
forces. There is no shortage of non-gravitational forces in the
Galactic center, either, strong magnetic fields, stellar winds, etc.

When stellar velocities became available, they matched the gas
velocities.

Reference, please. I think you'll find that there are either NO stars or O
and B stars.

I'd be happy to be disproved. I've been asking for any paper to the
contrary for years.

greywolf42
ubi dubium ibi libertas