A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Research
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Galaxies without dark matter halos?



 
 
Thread Tools Display Modes
  #1  
Old July 9th 03, 10:18 PM
Ed Keane III
external usenet poster
 
Posts: n/a
Default Galaxies without dark matter halos?

John Baez wrote in message
...

In article ,
Norm Dresner wrote:

Since it's believed that there's a dark matter "halo" around or

containing
every normal matter galaxy, [...]


Just to throw an interesting spanner in the works, the April 11th
issue of Science reports that Aaron Romanowsky at the University of
Nottingham claims to have found some galaxies *without* dark matter
halos.

Other astronomers are skeptical, so we should wait to see whether
this gets confirmed or refuted. But if it were true, it would probably
be a big deal. For one, it would probably kill all MOND-like theories
in which dark matter is just an artifact of not understanding gravity
well enough. For two, folks would have a lot of fun trying to explain
such a thing could happen.



It is suggested that it was stripped away through interaction with other
galaxies. One characteristic of ellipticals is that they often do not have
concentrated mass cores. Does anyone know if this is true for these?

Another thing I am curious about is whether the motion of these galaxies
with respect to others also indicates that they are not surrounded by dark
matter. It seems to me that if it turns out that galaxies without
concentrated cores do not contain dark matter within their visible limits
but seem to still be surrounded by it could indicate a problem with our
understanding of the gravitational dynamics around massive cores. I gather
that some people think the dark matter problem could be associated with
black holes and that would be ruled out. And explaining it with dark matter
would at least get more complicated.

-Ed Keane III
  #2  
Old July 30th 03, 10:23 AM
Thomas Smid
external usenet poster
 
Posts: n/a
Default Galaxies without dark matter halos?

It has never been the case that all galaxies show evidence for dark
matter halos (see http://nedwww.ipac.caltech.edu/level5/March01/Battaner/).
The point is that the observed anomalous rotation curves of galaxies
are practically always based on gas velocities which can be very
different from the velocities of stars ( see my webpage
http://www.physicsmyths.org.uk/darkmatter.htm for an alternative
interpretation of the constant velocity curves in this sense).
  #3  
Old July 30th 03, 10:23 AM
Thomas Smid
external usenet poster
 
Posts: n/a
Default Galaxies without dark matter halos?

It has never been the case that all galaxies show evidence for dark
matter halos (see http://nedwww.ipac.caltech.edu/level5/March01/Battaner/).
The point is that the observed anomalous rotation curves of galaxies
are practically always based on gas velocities which can be very
different from the velocities of stars ( see my webpage
http://www.physicsmyths.org.uk/darkmatter.htm for an alternative
interpretation of the constant velocity curves in this sense).
  #4  
Old July 31st 03, 07:15 PM
greywolf42
external usenet poster
 
Posts: n/a
Default Galaxies without dark matter halos?

Jason Rhodes wrote in message
...
Your theory of the origin of galactic rotation curves fails to account for
recent measurements of the dark matter haloes by means of weak

gravitational
lensing.


I belive you've gone circular, here. Without "dark matter" the big bang's
current incarnation is dead. The "measurement" of distance used in those
"lensing" studies assumes the big bang (pure doppler for the Hubble
constant). Hence your mass estimates are worthless for the purpose of
discriminating between dark matter and non-dark matter.

greywolf42
ubi dubium ibi libertas

[Mod. note: of course, the distance-redshift conversion for distant
objects is not `pure Doppler', but it does assume that the universe is
expanding -- mjh.]
  #5  
Old July 31st 03, 07:15 PM
greywolf42
external usenet poster
 
Posts: n/a
Default Galaxies without dark matter halos?

Jason Rhodes wrote in message
...
Your theory of the origin of galactic rotation curves fails to account for
recent measurements of the dark matter haloes by means of weak

gravitational
lensing.


I belive you've gone circular, here. Without "dark matter" the big bang's
current incarnation is dead. The "measurement" of distance used in those
"lensing" studies assumes the big bang (pure doppler for the Hubble
constant). Hence your mass estimates are worthless for the purpose of
discriminating between dark matter and non-dark matter.

greywolf42
ubi dubium ibi libertas

[Mod. note: of course, the distance-redshift conversion for distant
objects is not `pure Doppler', but it does assume that the universe is
expanding -- mjh.]
  #6  
Old August 1st 03, 10:10 AM
Jason Rhodes
external usenet poster
 
Posts: n/a
Default Galaxies without dark matter halos?

"greywolf42" wrote in message
...
I belive you've gone circular, here. Without "dark matter" the big bang's
current incarnation is dead. The "measurement" of distance used in those
"lensing" studies assumes the big bang (pure doppler for the Hubble
constant). Hence your mass estimates are worthless for the purpose of
discriminating between dark matter and non-dark matter.


That is incorrect. The distance measurements were not inferred from earlier
dark matter measurements, as your claim of circular reasoning would imply.

However, if you fail to believe the preponderance of evidence pointing
toward a big bang universe, another completely independent measurement using
an unrelated methodology that supports the currently accepted big bang
cosmology is unlikely to change your view.

I'd be interested to see a demonstration of an alternative view that can
explain all the previous measurements as well as recent lensing
measurements.

Jason

[Mod. note: so would everyone else, but posters trying to meet this
challenge should bear in mind the s.p.r. and s.a.r. moderation
criteria -- mjh.]
  #7  
Old August 1st 03, 10:10 AM
Jason Rhodes
external usenet poster
 
Posts: n/a
Default Galaxies without dark matter halos?

"greywolf42" wrote in message
...
I belive you've gone circular, here. Without "dark matter" the big bang's
current incarnation is dead. The "measurement" of distance used in those
"lensing" studies assumes the big bang (pure doppler for the Hubble
constant). Hence your mass estimates are worthless for the purpose of
discriminating between dark matter and non-dark matter.


That is incorrect. The distance measurements were not inferred from earlier
dark matter measurements, as your claim of circular reasoning would imply.

However, if you fail to believe the preponderance of evidence pointing
toward a big bang universe, another completely independent measurement using
an unrelated methodology that supports the currently accepted big bang
cosmology is unlikely to change your view.

I'd be interested to see a demonstration of an alternative view that can
explain all the previous measurements as well as recent lensing
measurements.

Jason

[Mod. note: so would everyone else, but posters trying to meet this
challenge should bear in mind the s.p.r. and s.a.r. moderation
criteria -- mjh.]
  #8  
Old August 4th 03, 12:37 PM
greywolf42
external usenet poster
 
Posts: n/a
Default Galaxies without dark matter halos?

Jason Rhodes wrote in message
...
"greywolf42" wrote in message
...
I belive you've gone circular, here. Without "dark matter" the big

bang's
current incarnation is dead. The "measurement" of distance used in

those
"lensing" studies assumes the big bang (pure doppler for the Hubble
constant). Hence your mass estimates are worthless for the purpose of
discriminating between dark matter and non-dark matter.


That is incorrect. The distance measurements were not inferred from

earlier
dark matter measurements, as your claim of circular reasoning would imply.


I neither claimed nor implied mass estimates were based on earlier 'dark
matter' measurements. They are based on 'big bang' DISTANCE measurements.

We are attempting to determine whether 'dark matter' exists, based on
lensing estimates. Dark matter is inferred whenever we compare two
disparate mass estimates. The first is when we calculate a mass of a galaxy
based on it's apparent visible stars (actually overall absolute
luminosity) -- which roughly 'counts' the number of visible stars and
(through theory) low-luminosity normal matter objects. This mass estimate
requires us to know the distance to the galaxy. Distances to galaxies
(those used in lensing papers) are determined SOLELY through the assumption
of the big bang -- that the measured redshift converts directly to a
distance.

The second mass estimate is based on the 'gravitational lensing' of a second
galaxy behind the first. The amount of lensing (angle of bend) is based on
two distances -- both determined solely by the big-bang theory (redshift IS
distance). The apparent bend of the light is then used to infer a mass of
the galaxy with the smaller redshift (presumed to be closer).

Now if the redshift - distance postulate is not universally correct under
all conditions, then (at the truly cosmic distances indicated) then not only
is the 'visible mass' estimate in error, the deflection angle (and the
'total mass' estimate) are both going to be incorrect.

The big bang relies upon dark matter to stay viable (otherwise omega is
nowhere near 1). Thus, "your mass estimates are worthless for the purpose
of discriminating between dark matter and non-dark matter."


However, if you fail to believe the preponderance of evidence pointing
toward a big bang universe, another completely independent measurement

using
an unrelated methodology that supports the currently accepted big bang
cosmology is unlikely to change your view.


I'm not aware of any preponderance of evidence for the big bang. Every time
there is a new observation at odds with the big bang (i.e. omega = .02
instead of 1, Hubble constant failure at high redshift), a "new" physical
phenomenon is invented to patch up the structure ('dark matter', 'dark
energy').

I'd be interested to see a demonstration of an alternative view that can
explain all the previous measurements as well as recent lensing
measurements.

[Mod. note: so would everyone else, but posters trying to meet this
challenge should bear in mind the s.p.r. and s.a.r. moderation
criteria -- mjh.]


How about one that predicted the hubble constant failure at high z, instead
of creating 'dark energy' as the latest epicycle (ad hoc)? Start with the
book "The Big Bang Never Happened", by Lerner. Then we can discuss the
measurements that you feel weigh more heavily on one side or the other.

greywolf42
ubi dubium ibi libertas
  #9  
Old August 4th 03, 12:37 PM
greywolf42
external usenet poster
 
Posts: n/a
Default Galaxies without dark matter halos?

Jason Rhodes wrote in message
...
"greywolf42" wrote in message
...
I belive you've gone circular, here. Without "dark matter" the big

bang's
current incarnation is dead. The "measurement" of distance used in

those
"lensing" studies assumes the big bang (pure doppler for the Hubble
constant). Hence your mass estimates are worthless for the purpose of
discriminating between dark matter and non-dark matter.


That is incorrect. The distance measurements were not inferred from

earlier
dark matter measurements, as your claim of circular reasoning would imply.


I neither claimed nor implied mass estimates were based on earlier 'dark
matter' measurements. They are based on 'big bang' DISTANCE measurements.

We are attempting to determine whether 'dark matter' exists, based on
lensing estimates. Dark matter is inferred whenever we compare two
disparate mass estimates. The first is when we calculate a mass of a galaxy
based on it's apparent visible stars (actually overall absolute
luminosity) -- which roughly 'counts' the number of visible stars and
(through theory) low-luminosity normal matter objects. This mass estimate
requires us to know the distance to the galaxy. Distances to galaxies
(those used in lensing papers) are determined SOLELY through the assumption
of the big bang -- that the measured redshift converts directly to a
distance.

The second mass estimate is based on the 'gravitational lensing' of a second
galaxy behind the first. The amount of lensing (angle of bend) is based on
two distances -- both determined solely by the big-bang theory (redshift IS
distance). The apparent bend of the light is then used to infer a mass of
the galaxy with the smaller redshift (presumed to be closer).

Now if the redshift - distance postulate is not universally correct under
all conditions, then (at the truly cosmic distances indicated) then not only
is the 'visible mass' estimate in error, the deflection angle (and the
'total mass' estimate) are both going to be incorrect.

The big bang relies upon dark matter to stay viable (otherwise omega is
nowhere near 1). Thus, "your mass estimates are worthless for the purpose
of discriminating between dark matter and non-dark matter."


However, if you fail to believe the preponderance of evidence pointing
toward a big bang universe, another completely independent measurement

using
an unrelated methodology that supports the currently accepted big bang
cosmology is unlikely to change your view.


I'm not aware of any preponderance of evidence for the big bang. Every time
there is a new observation at odds with the big bang (i.e. omega = .02
instead of 1, Hubble constant failure at high redshift), a "new" physical
phenomenon is invented to patch up the structure ('dark matter', 'dark
energy').

I'd be interested to see a demonstration of an alternative view that can
explain all the previous measurements as well as recent lensing
measurements.

[Mod. note: so would everyone else, but posters trying to meet this
challenge should bear in mind the s.p.r. and s.a.r. moderation
criteria -- mjh.]


How about one that predicted the hubble constant failure at high z, instead
of creating 'dark energy' as the latest epicycle (ad hoc)? Start with the
book "The Big Bang Never Happened", by Lerner. Then we can discuss the
measurements that you feel weigh more heavily on one side or the other.

greywolf42
ubi dubium ibi libertas
  #10  
Old August 8th 03, 10:40 AM
Jeffery
external usenet poster
 
Posts: n/a
Default Galaxies without dark matter halos?

If you deny the Big Bang, how do explain the redhift of the galaxies?
How do explain the CMB? How do you explain the isotropy of the CMB to
1 part in 10^5? The evidence for the Big Bang is beyond overwhelming.

A separate question is whether the Universe existed for an infinite
length of time. Within the inflationary model, you could have eternal
inflation. So the irony is that inflation, which saved the Big Bang
model, could ultimately allow the possibility that the Universe could
have existed for an infinite length of time after all.

Jeffery Winkler

http://www.geocities.com/jefferywinkler
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
"Dark matter" forms dense clumps in ghost universe (Forwarded) Andrew Yee Astronomy Misc 0 November 21st 03 05:41 PM
Galaxies without dark matter halos? greywolf42 Astronomy Misc 34 November 5th 03 01:34 PM
A Detailed Map of Dark Matter in a Galactic Cluster Reveals How Giant Cosmic Structures Formed Ron Baalke Astronomy Misc 3 August 5th 03 02:16 PM
Galaxies without dark matter halos? Ed Keane III Research 4 August 4th 03 12:39 PM
Hubble tracks down a galaxy cluster's dark matter (Forwarded) Andrew Yee Astronomy Misc 0 July 17th 03 01:42 PM


All times are GMT +1. The time now is 09:32 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.