What Does XMM-Newton Reveal About Dark Energy in the X-ray Universe?

[hellfire]

wolram, regarding your last reference: I have been reading some references and I think the process of cooling of the intra cluster gas is not relevant in this case. Cooling refers to the loss of energy due to the x-ray emissions (which are generated due to thermal bremsstrahlung) and its characteristic time is of the scale (or usually longer than) the Hubble time for most of the clusters. It is therefore usualy not considered for time evolution of the luminosity. As far as I understood, Blanchard also does not consider the cooling effect for his main argumentation.

My impression now is that x-ray emission depends not only on the potential well, but on a function called density contrast. This is the quotient of the main density of the cluster (density perturbation) and the energy density of the universe at the time where the cluster gets virialized (more or less stability of the gravitationally bound system is reached).

In general, it is the number of clusters of a given virial mass, which depends on the density contrast, but, since there is a postulated relation between luminosity and virial mass, also the emission of x-rays should depend on the density contrast.

Blanchard claims to have found more x-rays than today. I thought this implies deeper potential wells (in contradiction with Blanchards own thesis) but it seams that this is not the case due to the dependence on the density contrast function.

Due to the relation between density and radius the cosmological constant enters the density contrast function making use of the Friedmann equation. I am not able now to make any qualitative statement about the relations. As you see I just think now I have found the right equations, but I am still far from understanding properly the effect of evolution of luminosity.

Anyway, it would be great if somebody could confirm or correct me.

These are the references I used:
http://arxiv.org/astro-ph/9611085
http://nedwww.ipac.caltech.edu/level5/March02/Sarazin/Sarazin_contents.html
http://nedwww.ipac.caltech.edu/level5/Sept02/Padmanabhan/Pad_contents.html

Regards.

 

[Nereid]

Originally posted by marcus
the more explaining you do on PF the easier to understand
you get

6 months ago you only asked one-line questions
and the more questions you asked the better they got
now you elucidate and the more you
practice the better it gets
(hellfire and Nereid may have noticed, why should I jump in?)

today is Greg B's 21 birthday
what shall we say to him on this occasion
except that we see that the PF he has built
seems now and then to be good for something
beyond simple recreation

This thread is roaring along so quickly, it's scary I've started to reply to some post or other here several times, only to find, upon reading more of the thread, that some other aspect needs to be covered (or has already been covered). Whew, what a ride!

Someone may have commented on this already (yes, I've been in the slow class several times), but Peacock's paper on large scale structure and cosmology may be quite interesting to several readers (see if you can ignore the equations wolfram, and get an idea of the logic; you may also pick up a thing or two about some of those puzzling parameters which you read in other papers, e.g. 'tilt', 'bias', 'tensors').

 

[marcus]

I've been distracted from this thread by other (local off-web) activity and also swamped by the complexity of the issues. I need to find a suitable tutorial and an up-to-date review article that surveys how things stand at present and how the various investigations into dark energy are going.

Right now I am convinced that several of you other posters (hellfire, wolram, Nereid) are ahead of me and I need to catch up.

This morning over coffee I looked at Sahni's review article
"Dark Matter and Dark Energy"
http://arxiv.org./astro-ph/0403324

You can tell its meant as a review article because it has 190 references in its bibliography

You can tell its meant to be understandable to a wider audience because it doesn't explain very much in detail.

It is the sort of thing that OUGHT to help, but instead of helping integrate, it zaps my understanding by showing me that the jigsaw puzzle has 1000 pieces rather than the 100 or so I expected. I should be grateful to Nature for being so complex? Is this a sign something really interesting will emerge? Or is this just the wrong review article to try to read? Maybe there is a better one

 

[marcus]

Varun Sahni's Figure 1 is a graphic undeniable demonstration of the existence of dark matter:
the rotation curve for M33 keeps going up!

"It is interesting that the total mass of an individual
galaxy is still somewhat of an unknown quantity since a turnaround to the v ~ r^−1/2 law at large radii has not been convincingly observed." (page 4)

Can this be true? They have not even seen where the rotation curve
stops increasing and begins to decline? The situation is more confusing than I thought.



In the most basic entry-level details of the picture, there are unexpected signals. here is some more on page 4:

"An important difference between the distribution of dark matter in galaxies and clusters needs to be emphasised: whereas dark matter appears to increase with distance in galaxies, in clusters exactly the reverse is true, the dark matter distribution actually decreases with distance..."

so clusters of galaxies have a central concentration of DM but individual galaxies do not-----their DM is spread out an order of magnitude more than their visible matter. And he emphasizes this aspect by giving a little evidence:

"...Indeed, for certain dwarfs (such as DD0154) the rotation curve has been measured to almost 15 optical length scales indicating that the dark matter surrounding this object is extremely spread out (see also figure 1).

A foreground cluster, on the other hand, acts as a gravitational lens which focuses the light from background objects such as galaxies and QSO’s thereby allowing us to determine the depth of the cluster potential well. Observations of strong lensing by clusters indicate
that dark matter is strongly concentrated in central regions with a projected mass of 10¹³ − 10¹⁴ solar masses being contained within 0.2 - 0.3 Mpc of the central region. As we shall see later, this observation may prove to be problematic for alternatives to the dark matter hypothesis such as the Modified Newtonian..."

Then there is the business of the Xray-emitting gas. Varun Sahni says that even the visible matter in clusters of galaxies is not what I thought it was. It is not stars, he says, most of the mass of visible matter in a cluster is in the form of Xray-emitting gas!

"The mass-to-light ratio in clusters can be as large as M/L = 300M_sol/L_sol. However since most of the mass in clusters is in the form of hot, x-ray emitting intracluster gas, the extent of dark matter in these objects is estimated to be M/M_lum = 20, where M_lum is the total mass in luminous matter including stars and gas."

If this is true it will take a bit of getting used to.
the U has right amount of energy density to make it flat
and most of that energy isn't matter, it is DE
but there is some matter
however most of the matter isn't visible it is DM
on the other hand there is some visible matter
but (before you get too comfortable with that, notice that)
the visible matter is mostly not stars it is visible by
its Xrays because the great bulk of it is Xray-emitting gas.

I had accepted the idea that only 4 percent of the U was
ordinary baryonic matter and I decided to be content with that,
but I thought it at least was stars. Now I find that the
4 percent is mostly Xray-emitting gas. Bah. I shall write the
editors of Nature and threaten to cancel my subscription if
they cannot abide by the rules of ordinary decency

 

[marcus]

Something almost funny in Varun Sahni's review article.
the speed of the Earth relative to galactic center varies, being 7 percent faster in the summer than in the winter

so the Earth should bump into more dark matter in the summer

a controversy has arisen because a research group called DAMA
claims to have detected this bumping
with an annual variation just as predicted:
more bumping in the summer

but regretfully it must be said that not a single other research group has been able to reproduce this result

the controversy and lack of confirmation does not deter Sahni from including this in his review and he also has a nice little picture of the Earth going around the sun to explain why the speed varies by 7 percent----Figure 3 on page 8

 

[wolram]

thanks STINGRAY.
it seems that the properties of these early type galaxies
are Dependant on the potential energy of dark matter rather
than any barionic mechanisms, i am catching up your last
post helped lots.
thanks for link NEREID your observation on the speed of
this thread just hit me, i think i spent all my fuel to
early and now have to coast, but that will be enjoyable
as i have lots to read.

 

[wolram]

by MARCUS.
Something almost funny in Varun Sahni's review article.
the speed of the Earth relative to galactic center varies, being 7 percent faster in the summer than in the winter

this is a strange comment.

 

[marcus]

Originally posted by wolram
by MARCUS.
...this is a strange comment.

Pax wolram. :-)

One research group has detected us plowing through dark matter
ever since 1996
but no other group is able to sense this happening.

 

[Nereid]

Originally posted by marcus I've been distracted from this thread by other (local off-web) activity and also swamped by the complexity of the issues. I need to find a suitable tutorial and an up-to-date review article that surveys how things stand at present and how the various investigations into dark energy are going.

Right now I am convinced that several of you other posters (hellfire, wolram, Nereid) are ahead of me and I need to catch up.

This morning over coffee I looked at Sahni's review article
"Dark Matter and Dark Energy"
http://arxiv.org./astro-ph/0403324

You can tell its meant as a review article because it has 190 references in its bibliography

You can tell its meant to be understandable to a wider audience because it doesn't explain very much in detail.

It is the sort of thing that OUGHT to help, but instead of helping integrate, it zaps my understanding by showing me that the jigsaw puzzle has 1000 pieces rather than the 100 or so I expected. I should be grateful to Nature for being so complex? Is this a sign something really interesting will emerge? Or is this just the wrong review article to try to read? Maybe there is a better one

This is, IMHO, a good review! Of course, it could have been longer (there's always more you want to know ).

AND it has the figure that I was trying to find for a previous post! It's figure 11, on page 33.

Originally posted by marcus
Can this be true? They have not even seen where the rotation curve stops increasing and begins to decline? The situation is more confusing than I thought.

Er, yes, it's true. But it's not a problem, because the mass in clusters is constrained by other estimates, and what are clusters but many galaxies (including 'dark' ones) and 'some' IGM?

Originally posted by marcus Then there is the business of the Xray-emitting gas. [a.k.a. IGM] Varun Sahni says that even the visible matter in clusters of galaxies is not what I thought it was. It is not stars, he says, most of the mass of visible matter in a cluster is in the form of Xray-emitting gas!

Omigosh! hock! Shorror! Lends a whole new meaning to the phrase 'scum of the universe', doesn't it?

 

[Nereid]

Originally posted by marcus
One research group has detected us plowing through dark matter ever since 1996 but no other group is able to sense this happening.

So maybe those researchers found something else in 1996?

Anyway, won't it be nice when we detect some real, honest-to-Hoyle neutralinos, binos, winos, higgsinos, axions, Wimpzillas, axinos, or gravitinos?

 

[marcus]

Originally posted by Nereid
So maybe those researchers found something else in 1996?

Anyway, won't it be nice when we detect some real, honest-to-Hoyle neutralinos, binos, winos, higgsinos, axions, Wimpzillas, axinos, or gravitinos?

they sound like the breakfast cereals from when I was a kid

 

[wolram]

by MARCUS

I've been distracted from this thread by other (local off-web) activity and also swamped by the complexity of the issues. I need to find a suitable tutorial and an up-to-date review article that surveys how things stand at present and how the various investigations into dark energy are going.
--------------------------------------------------------------------
looking for answers about DM, DE, is akin to a search for the
holy grail, to date i have found only "observational evidence".

 

[wolram]

http://eu.spaceref.com/news/viewpr.html?pid=7050

Big bang nucleosynthesis theory provides an estimate on the amount of "ordinary" matter in the Universe, and this rules out the possibility that dark matter is from dim stars, dark chunks of solid material or black holes. Dark matter must be exotic, that is, not made of protons and electrons. Various observations with radio, optical and X-ray telescopes aim to determine the distribution and nature of dark matter.

 

[Nereid]

Originally posted by wolram
*SNIP
looking for answers about DM, DE, is akin to a search for the holy grail, to date i have found only "observational evidence".

My goodness, what on Earth (M33, Abell 1835 IR1916, ...) is there apart from observational evidence? OK, and maybe coming into the lab in the morning and finding a nice healthy green Wimpzilla in your SQUID.

 

[wolram]

i agree NEREID bad choise of words.
----------------------------------------


IN one of those interesting intersections of particle physics, astrophysics, and cosmology, scientists from Lawrence Livermore National Laboratory, the University of California at Berkeley (UCB), the University of Florida (UF), and the National Radio Astronomy Observatory (NRAO) have joined together to try to pin down an elusive particle. This particle, called the axion, if it is found to exist and is not just a hypothesis, would be a long-sought relic from the first fractional second of the birth of the universe and one of the most weakly interacting particles known. Experimental verification of the existence of the axion would not only help “balance the budget” for the missing mass of the universe but also clear up one of the thorniest issues in particle physics.
---------------------------------------------------------------------
i have lost the url for this paper anyone have a link?
---------------------------------------------------------------------
it seems to me that cold DM is the most favoured candidate
for the missing mass problem, is this correct?

 

[Nereid]

wolfram: it seems to me that cold DM is the most favoured candidate for the missing mass problem, is this correct?

Yes.

 

[meteor]

A not very well known model of Dark energy is the model known as quartessence. In fact, quartessence is multifaceted, plays both the role of dark energy and dark matter.
Eh, I said role marcus, remember?

 

[wolram]

http://de.arxiv.org/abs/astro-ph/0401032

I describe recent challenges in hierarchical galaxy formation theory, including the formation of disk galaxies and of ellipticals. Problems with cold dark matter are summarized, and possible solutions are presented. I conclude with a description of the prospects for observing one of the most important ingredients in galaxy formation theory, namely cold dark matter.
--------------------------------------------------------------------
the bottom up theory of evolution has problems ,but they seem
to be mechanical, and not insurmountable.

 

[meteor]

"Cosmology with tachyon field as dark energy"
http://arxiv.org/abs/astro-ph/0212198

It can be a good idea if they are able to find some day the elusive tachyon

I insist that is not necessary that dark energy is due to a constant field (e.g. cosmological constant). A model with a variable scalar field would also fit the data. Quintessence is an example of such a model. And, I will go further and I conjecture that quintessence=Higgs field
Ok, call me crackpot now

 

[Nereid]

Any specific predictions from this theory, that sets it clearly apart from other dark energy theories? I mean, other than catching a tachyon in your lab SQUID while you're eating your breakfast cereal.

 

[Nereid]

Originally posted by wolram
http://de.arxiv.org/abs/astro-ph/0401032

I describe recent challenges in hierarchical galaxy formation theory, including the formation of disk galaxies and of ellipticals. Problems with cold dark matter are summarized, and possible solutions are presented. I conclude with a description of the prospects for observing one of the most important ingredients in galaxy formation theory, namely cold dark matter.
--------------------------------------------------------------------
the bottom up theory of evolution has problems ,but they seem
to be mechanical, and not insurmountable.

This was written before the recent INTEGRAL results on the source of the 'diffuse' gammas from the galactic centre, so this 'problem' has now gone away:
"The \gamma-ray flux towards the galactic centre is observed to have a hard spectrum (as expected for annihilations), but the clumps would not survive the tidal disruptions that are inevitable in the inner galaxy [29]. To account for the observed diffuse gamma ray flux from the direction of the galactic centre, one would need to have a very steep density profile (\rho \varpropto~ r^−1.5). This would conflict with microlensing observations and the inner rotation curve of the Galaxy.[/color]"

Silk's introduction is worth repeating:
"Galaxy formation theory must account for the properties and evolution of galaxies, the star formation rate, the spectral energy distribution and galaxy morphologies. Another important confrontation with observation is with the scaling relations. These relations (e.g. Tully-Fisher, fundamental plane) are controlled by the current relaxation time-scales (dynamical and chemical) which are long compared to the age of the universe. This is not an easy task because the theory is almost entirely phenomenological and is driven by the observations. The ultimate aim is to make predictions at high redshift for the current and future generations of powerful detectors and very large telescopes. Progress is inevitably iterative and slow, and observations are usually well ahead of theory. A major hurdle is that there is nof undamental theory of star formation. Major uncertainties include the initial stellar mass function, the star formation efficiency and the star formation rate. Of course, the empirical evidence for star formation is overwhelming, and this leaves cosmologists with little choice but to extract every possible output from their theories.[/color]"

[Edit: fixed formats]

 

[wolram]

METEOR.
i think the tachyon is out of favor, it seems to exotic,
the higgs could be tested soon in accelerators, but i am
almost convinced that DE, DM exist, but with 70% of universe
missing anything is possible.

 

[meteor]

Nereid: I looked through the paper and couldn't find any prediction that differs with the model of cosmological constant. Obviously, the great difference is the presence of the tachyon! But I must admit that I'm quite a layperson and didn't understand half of the paper, and is possible that I have overlooked some distinction with other models

Wolram: is possible that the Higgs have been found. Look this thread
https://www.physicsforums.com/showthread.php?s=&threadid=16078

I will add an alternative model for dark energy that I've discovered this morning

It proposes that dark energy is due to a chaotic scalar field
"Chaotics scalar fields as models for dark energy"
http://arxiv.org/abs/astro-ph/0310479

There's another proposal that postulates that the universe is not really accelerating, but the dimming of the type Ia supernova that triggered all the dark energy business is due to a mechanism known as axion-photon mixing
"Cosmic acceleration vs axion-photon mixing"
http://arxiv.org/abs/astro-ph/0311495

Ahrg, so many papers and so little time to read them all...

 

[wolram]

by METEOR.
Wolram: is possible that the Higgs have been found. Look this thread
-------------------------------------------------------------------
it would be fantastic if this could be verified, but it seems
the CL is quite low.

 

[wolram]

by METEOR.

There's another proposal that postulates that the universe is not really accelerating, but the dimming of the type Ia supernova that triggered all the dark energy business is due to a mechanism known as axion-photon mixing
"Cosmic acceleration vs axion-photon mixing"
--------------------------------------------------------------------
this is a hill that we can never get to the top of, the axion
is another thing that is proposed but not found, its good to
speculate but one can't climb an imaginary hill.

 

[meteor]

Another curious theory
http://arxiv.org/abs/astro-ph/0308183

Dark energy and dark matter from an inhomogeneous dilaton
Authors: Mikel Susperregi
Comments: 9 pages, 8 figures, uses revtex, submitted PRD
Journal-ref: Phys.Rev. D68 (2003) 123509

A cosmological scenario is proposed where the dark matter (DM) and dark energy (DE) of the universe are two simultaneous manifestations of an inhomogenous dilaton. The equation of state of the field is scale-dependent and pressureless at galactic and larger scales and it has negative pressure as a DE at very large scales. The dilaton drives an inflationary phase followed by a kinetic energy-dominated one, as in the "quintessential inflation" model introduced by Peebles & Vilenkin, and soon after the end of inflation particle production seeds the first inhomogeneities that lead to galaxy formation. The dilaton is trapped near the minimum of the potential where it oscillates like a massive field, and the excess of kinetic energy is dissipated via the mechanism of "gravitational cooling" first introduced by Seidel & Suen. The inhomogeneities therefore behave like solitonic oscillations around the minimum of the potential, known as "oscillatons", that we propose account for most DM in galaxies. Those regions where the dilaton does not transform enough kinetic energy into reheating or carry an excess of it from regions that have cooled, evolve to the tail of the potential as DE, driving the acceleration of the universe.

Here dark energy is caused by the famous dilaton, the scalar field that appears in superstring theory.
Wolram: the axion was postulated to solve the so-called strong CP problem, and is a serious candidate to Cold dark matter

 

[wolram]

METEOR.
i can't comment on this one the math is to much for me,
as for all these proposed particles i just don't know,
DM,DE is so unintuitive that i would prefer an alternative,
but unless i go out and find one and get it approved by
mainstream science i am stuck with it, what is your view?

 

[wolram]

from WIKIPEDIA.

--------------------------------------------------------------------------------

The axion is a hypothetical particle postulated by Peccei-Quinn theory to resolve the strong-CP problem in quantum chromodynamics (QCD). The naive first principles formulation of QCD without axions predicts that some strong interactions will violate CP-symmetry. This is never observed in practice, and the axion was postulated to be a particle (specifically a pseudo-Goldstone boson) associated with a new broken symmetry of nature, whose conservation is constructed to exclude all CP-violating terms from QCD.

Axions are predicted to have no charge, very low mass (10-6 - 10-2 eV/c2) and very low interaction cross-sections for strong and weak forces. Hence they are nearly invisible to ordinary matter, and cannot be excluded on the basis of current measurements, though they have never been observed.

The predictions of axion theories would lead to them being created abundantly during the big bang. Because of a unique coupling to the instaton field of the primordial universe (i.e. "misalignment mechanism"), an effective dynamical friction is created during the acquisition of mass following cosmic inflation, this robs all such primordial axions of their kinetic energy. Hence axion theories predict that the universe will be filled with a very cold Bose-Einstein condensate of primordial axions. Depending on their mass, axions could plausibly explain the dark matter problem of cosmology. Observational studies to detect dark matter axions are underway, but they are not yet sufficiently sensitive to probe the mass regimes where axions would be expected to be found if they are the solution to the dark matter problem. Such studies have excluded the possibility of high mass axions.

It should be noted that the existence of axions are also a necessary component of string theory.

 

[Nereid]

So many theories, so little in the way of observational constraints!

Well, that's not entirely accurate - the observations are very extensive (for example, only last week SDSS announced the release of 6 terabytes of data to the public!), it's more that the observations don't seem (yet) to constrain the theories much. And the theories aren't investigated well enough (in general).

Personally, I rejoice in the observational advances, and am happy to wait for consensus to emerge over a period of five years or so.

Of course, if someone manages to catch a neutralino or three ...

[Edit: fixed spelling ]

 

[meteor]

Add this to the zoo of theories trying to explain dark energy:
"Phantom k-essence cosmologies"
http://arxiv.org/abs/astro-ph/0403157

Ah, and beware of the "phantom tachyon"