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#1
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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 |
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