Dark Matter Particle: Top Candidates

[Mike2]

The king profile assumes an inner slope dark matter density profile of 0, as compared to 1.0 for NFW and 1.5 for Moore. The calculation is otherwise the same. The higher the slope, the more peaked the matter distribution towards the center.

I must have missed something. Do you have a link to these different DM models? Could you explain a little more about this "slope"? Thanks.

The 'best fit' profile appears to vary depending on age and level of interaction between structures. Older, less interactive structures tend to be flatter [king profile] whereas younger, more interactive structures tend toward steeper distributions.

As far as the lensing effect goes, could it be possible that the older clusters are traveling faster (more redshifted) and so light has more time to feel the gravity of these older galaxies as they pass by? Whereas the younger galaxies are moving much slower compared to these early ones so that light feel these younger galaxies as if those galaxies were more or less standing still?

Did I read right that it is only the spiral galaxies that show more lensing effect than expected?

 

[Chronos]

I must have missed something. Do you have a link to these different DM models? Could you explain a little more about this "slope"? Thanks.


As far as the lensing effect goes, could it be possible that the older clusters are traveling faster (more redshifted) and so light has more time to feel the gravity of these older galaxies as they pass by? Whereas the younger galaxies are moving much slower compared to these early ones so that light feel these younger galaxies as if those galaxies were more or less standing still?

Did I read right that it is only the spiral galaxies that show more lensing effect than expected?

Start here
http://www.mrao.cam.ac.uk/~hjb26/thesis/node6.html

 

[Nereid]

Did I read right that it is only the spiral galaxies that show more lensing effect than expected?

yanniru stated this, but when I checked the paper from which he got the idea, I found it referenced only one source, and upon checking that I found the study was limited to three, carefully selected ellipticals, none of which seemed to have a DM profile of the kind predicted. However, the authors of this study did clearly state that other work had found strong evidence of DM profiles (as predicted by LCDM models?) in both massive (cD) and dwarf ellipticals. If you look at the cluster analysis done by the Bell Labs team, you will see that plenty of the ellipticals generate lensing signals. IIRC, an early SDSS statistical study also found that lensing was pretty much independent of Hubble type (it would be interesting to see this work repeated with the newer SDSS releases, and the aggregated data). Of course, this work was statistical, so there is probably no easy way to extract galaxies which show much less lensing than expected (or maybe not ... anyone interested to work out an algorithm? anyone have access to the necessary resources to do the work?? Join PF and do some real, on-line science?)

 

[turbo]

How about turbo-1's favourite - ZPE, or an extension/replacement for GR in rich clusters (and heavy galaxies, and SMBHs)? AFAIK, the problem here is a lack of theory - there's plenty of good, local data that could be used to test any such theories, but where are the theories?

I don't know what these authors are using for a justification for their proposed antimatter gravity experiment, although I hope they get the funding they need to pull it off. I have been trying to find a non pay-per-view version of this article on-line. Kluwer won't let me read the article unless I pay them $25. Can someone with a subscription summarize the authors' proposal and their justifications for me? Specifically, I would like to know why they want to measure the fall rate of antimatter.

BTW, Ingenta has the article, too, but they won't let me read it unless I pay them $31. They have a lot of articles regarding experimentation on the ISS, but at $31 each, I can't afford to read them.

http://ipsapp009.kluweronline.com/IPS/content/ext/x/J/4728/I/87/A/6/abstract.htm

http://www.ingenta.com/isis/browsing/TOC/ingenta?issue=pubinfobike://klu/gerg/2004/00000036/00000003

 

[Mike2]

yanniru stated this, but when I checked the paper from which he got the idea, I found it referenced only one source, and upon checking that I found the study was limited to three, carefully selected ellipticals, none of which seemed to have a DM profile of the kind predicted. However, the authors of this study did clearly state that other work had found strong evidence of DM profiles (as predicted by LCDM models?) in both massive (cD) and dwarf ellipticals. If you look at the cluster analysis done by the Bell Labs team, you will see that plenty of the ellipticals generate lensing signals. IIRC, an early SDSS statistical study also found that lensing was pretty much independent of Hubble type (it would be interesting to see this work repeated with the newer SDSS releases, and the aggregated data). Of course, this work was statistical, so there is probably no easy way to extract galaxies which show much less lensing than expected (or maybe not ... anyone interested to work out an algorithm? anyone have access to the necessary resources to do the work?? Join PF and do some real, on-line science?)

I wonder how fast the earliest galaxies were moving. It is supposed that the universe was decelerating in expansion from the beginning (until recently it has started to accelerate). So presumably galaxies were moving at their fastest speed when they first formed. Since it takes time for background light to pass a foreground galaxy, and foreground galaxies are traveling in the same direction as background photons (outward direction), would those background photons feel the gravity of those foreground galaxies for a longer period of time and be bent around those galaxies more than if the foreground galaxy was standing still? How fast were these foreground galaxies moving at the time the background photons were passing by? Do the computer simulation assume any significant speed of the foreground galaxies? Is the over lensing effect less profound for nearby galaxies? Thanks.

 

[Chronos]

Given the speed of light is invariant, the relative motion of galaxies in the foreground is of no consequence. Only mass need be considered for lensing effects.

 

[turbo]

Given the speed of light is invariant, the relative motion of galaxies in the foreground is of no consequence. Only mass need be considered for lensing effects.

There are some pretty smart people who disagree with you. They think the speed of light might be determined by the texture of the space-time that the light has to cross.

http://arxiv.org/abs/hep-th/9408016

http://arxiv.org/abs/gr-qc/9504041

http://arxiv.org/abs/astro-ph/0001441

The fact that "empty" space is actually a sea of virtual particles is proof that there is an aether. Densification or polarization of this field has implications for the refractive properties of space-time. Lenses are arrangements of matter in which the speed of light is slower (in our real world) than that of the SOL in a "vacuum". By extension, the space-time properties in very massive clusters (caused by ZPE gradients) should produce refractive effects that cannot be explained by the visible matter in the cluster.

 

[Mike2]

Given the speed of light is invariant, the relative motion of galaxies in the foreground is of no consequence. Only mass need be considered for lensing effects.

Granted that if the first early galaxies were moving very slowly with respect to light, then lensing would not be affected by the motion of the foreground galaxy. But I do not know how fast early galaxies were moving, do you? But if there were moving at some portion of light, say 1/3 that of light, then the backgound photons would feel the force of gravity for a longer period of time and be deflected more. I don't see yet what invariance would have to do with anything. Not only that, but the galaxies would acquire some portion of relativistic mass and the gravitational field associated with that.

 

[selfAdjoint]

Granted that if the first early galaxies were moving very slowly with respect to light, then lensing would not be affected by the motion of the foreground galaxy. But I do not know how fast early galaxies were moving, do you? But if there were moving at some portion of light, say 1/3 that of light, then the backgound photons would feel the force of gravity for a longer period of time and be deflected more. I don't see yet what invariance would have to do with anything. Not only that, but the galaxies would acquire some portion of relativistic mass and the gravitational field associated with that.

Surely the galaxies' own local motions were far less than c, and if you mean motion due to expansion, of course the galaxies were not and are not moving in that sense. Space is expanding, the remote galaxies are no more moving like that than we are.

 

[Chronos]

Granted that if the first early galaxies were moving very slowly with respect to light, then lensing would not be affected by the motion of the foreground galaxy. But I do not know how fast early galaxies were moving, do you? But if there were moving at some portion of light, say 1/3 that of light, then the backgound photons would feel the force of gravity for a longer period of time and be deflected more. I don't see yet what invariance would have to do with anything. Not only that, but the galaxies would acquire some portion of relativistic mass and the gravitational field associated with that.

Galaxies moving slowly with respect to light? Light does not have a preferred reference frame. That is why the speed of light is called 'invariant'. And yes, I do know, given what I have read, how fast galaxies were moving in the past. It is called red shift. Your photon deflection model is not supported. Photons entering a gravitational field are blue shifted. When they exit, they are red shifted. The net effect is... zero.

 

[Chronos]

The fact that "empty" space is actually a sea of virtual particles is proof that there is an aether.

Really? That is a pretty bold assertion. Which version of aether do you have in mind, Lorentzian?

 

[turbo]

Really? That is a pretty bold assertion. Which version of aether do you have in mind, Lorentzian?

It's not bold at all. The vacuum of space is not empty, but is populated by zero-point energy fields. The EM ZPE field consists of a sea of self-annihilating virtual particle pairs, and this field exerts a measurable force, as demonstrated by the Casimir effect.

If you know anything about optics, you will know that light travels at different speeds in media of different densities. If you will glance at the papers I linked above, you will see that I am not the only person who has made the logical extension and arrived at the understanding that the speed of light can be affected by the density of the ZPE field through which it propagates. In fact, light propagating through a suppressed ZPE field (between the plates of a Casimir device) can be shown to travel faster than the speed of light in a "vacuum" (normal ZPE field).

"Empty" space isn't. The ZPE field predicted by QED has been proven to exist and its pressure has been measured using test equipment of various designs - not just the "two flat plates" configuration of the first model.

 

[Mike2]

Surely the galaxies' own local motions were far less than c, and if you mean motion due to expansion, of course the galaxies were not and are not moving in that sense. Space is expanding, the remote galaxies are no more moving like that than we are.

Well, let's see... durring inflation all matter was moving very fast, right? Then the force of gravity slowed matter even while it condensed to galaxies. I still don't know how fast those first galaxies were moving? Or was everything moving very slowly in comoving coordinates even during inflation?

 

[wolram]

If DM is cold and dark, how can it be proven, detected, if something most
think of as invariable isn't "c" for instance, please forgive my ignorance, but
it seems to me that this is a circular argument.

 

[Chronos]

Well, let's see... durring inflation all matter was moving very fast, right? Then the force of gravity slowed matter even while it condensed to galaxies. I still don't know how fast those first galaxies were moving? Or was everything moving very slowly in comoving coordinates even during inflation?

Agreed. They were moving very slowly in comoving coordinates even during inflation. As selfAdjoint pointed out, there is no evidence to suggest relativistic contributions to the mass of distant galaxies are any greater than for local galaxies [which is insignificant]. Cosmological red shift does not affect relativistic mass. Returning to the question of lensing of the CMBR, which is also relevant, see here.
http://home.fnal.gov/~scranton/LensedCMB/effect.html

If DM is cold and dark, how can it be proven, detected, if something most think of as invariable isn't "c" for instance, please forgive my ignorance, but
it seems to me that this is a circular argument.

Agreed. If 'c' is not invariant, a lot of modern theory turns into a mess. On the other hand, there is good evidence that 'c' has not detectably changed for billions of years, if ever [there are some possible anomalies if you go back 12 billion or so years].

 

[turbo]

Agreed. If 'c' is not invariant, a lot of modern theory turns into a mess. On the other hand, there is good evidence that 'c' has not detectably changed for billions of years, if ever [there are some possible anomalies if you go back 12 billion or so years].

C may be invariant over time. Time (history) may be irrelevant. C must be variable, however, based on the density of the media through which light propogates (basic optics). If the vacuum of space is not truly a "void", but in fact contains fields defined by the base-level energies predicted by QED (the zero-point energy fields), we must expect that the light propogating through these fields can be effected by the properties of these fields.

C as defined as "the speed of light through a vacuum" may only be an ideal, never to be reached. The real C (as a cosmological speed limit) may only be a virtual entity, with a serious dependence on conditions.

 

[Mike2]

Returning to the question of lensing of the CMBR, which is also relevant, see here.
http://home.fnal.gov/~scranton/LensedCMB/effect.html

This seems to suggest that the CMB is a backdrop farther away than the most distant galaxies? I didn't catch how much farther they assume the CMB to be. Nor did they explain how all this light got that far out? But, then again, they admit that this is only a simulation and that we do not yet possesses the capability to measure the CMB accurately enough to confirm this lensing of the CMB.

But wait, if the CMB photons were traveling since the beginning without scattering, then the photon that WE receive from the CMB must be the oldest photons of all. The photons from the photon soup that originate at every point and has been redshifted by expansion have photons originating at all points of space, but we only see those that are as old as recombination. CMB photons that were emitted nearer to us at the time of recombination have already past us by and are now headed away from us. We only see the oldest of the CMB. So we are seeing a backdrop. Is this right? Why does it seem that I have to be the one to explain everything?

What confuses me is if we can see these photons emitted so far away by the CMB, then how can there be any kind of horizon that is closer to us behind which galaxies are disappearing? Or is it that the CMB that we see IS the horizon. If so, then shouldn't it be even colder, in fact zero? Or will there come a time when we will no longer see the CMB? Or will the faint, red light of other galaxies take its place as the universe expands?

 

[Chronos]

This seems to suggest that the CMB is a backdrop farther away than the most distant galaxies? I didn't catch how much farther they assume the CMB to be. Nor did they explain how all this light got that far out? But, then again, they admit that this is only a simulation and that we do not yet possesses the capability to measure the CMB accurately enough to confirm this lensing of the CMB.

Agreed. The CMB is a backdrop to the most distant galaxies yet observed. The current suspect for most distant observed galaxy is z = 10. The CMB is around z = 1100.

But wait, if the CMB photons were traveling since the beginning without scattering, then the photon that WE receive from the CMB must be the oldest photons of all. The photons from the photon soup that originate at every point and has been redshifted by expansion have photons originating at all points of space, but we only see those that are as old as recombination. CMB photons that were emitted nearer to us at the time of recombination have already past us by and are now headed away from us. We only see the oldest of the CMB. So we are seeing a backdrop. Is this right?

Agreed.

Why does it seem that I have to be the one to explain everything?

That is just the way it works. You shouldn't believe anything until you can explain it to yourself.

What confuses me is if we can see these photons emitted so far away by the CMB, then how can there be any kind of horizon that is closer to us behind which galaxies are disappearing?

Agreed. It's not possible.

Or is it that the CMB that we see IS the horizon.

Yes.

If so, then shouldn't it be even colder, in fact zero?

No. It is exactly as cold as it should be given the age of the universe. The CMB photons we now detect had a temperature of about 3000k at the time they were emitted. The only thing that cools them down is red shift. Since they now are about a temperature of 2.75K, we know that recombination occurred at around z = 1100 [which blue shifts them back to the time they had a temperature of about 3000k].

Or will there come a time when we will no longer see the CMB? Or will the faint, red light of other galaxies take its place as the universe expands?

The CMB will gradually grow cooler and cooler, always approaching but never quite reaching absolute zero. No new galaxies will emerge from behind the CMB barrier.

 

[Mike2]

Chronos, you seem to be saying on the one hand that there is no horizons beyond which galaxies disappear. But on the other hand, you're saying that there is an expansion of the universe that can be faster than light. Or are you denying that the universe can expand faster than light? Where would that leave inflation? But if the universe can expand faster than light, then the photons from those regions will never reach us, right?

 

[Garth]

We have had this discussion before in the thread “Time Dilation & big bang Question”

First the CMB is not an event or particle horizon, in that radiation from beyond the surface of last scattering (SLS) still reaches us, it is just continuously scattered until it finally reaches the SLS. That is why the temperature of the CMB is not zero.

Whether objects in front of that scattering, whose red shifts are finite, are actually traveling faster than light or not depends on how you measure their velocity. That is, how you define and measure distance and time across the space-time curvature and cosmic expansion. One standard convention is to say you can observe cosmologically super-luminal objects. See http://bat.phys.unsw.edu.au/~charley/papers/0310808.pdf
Garth