Mapping the Dark Matter

Have any friends or colleagues who don’t believe in dark matter? Showing them this should help.

Dark Matter in Abell 1689

That ghostly haze is dark matter — or at least, an impression of the gravitational field created by the dark matter. This is galaxy cluster Abell 1689, in the constellation Virgo. (We feel compelled to add that information, in case you’re going to go looking for it in the night sky tonight or something.) It’s easy to see that the images of many of the galaxies have been noticeably warped by passing through the gravitational field of the cluster, a phenomenon known as strong gravitational lensing. This cluster has been studied for a while using strong lensing. The idea is that the detailed distribution of dark matter affects the specific ways in which different background images are distorted (similar to what was used to analyze the Bullet Cluster). Astronomers use up massive amounts of computer time constructing different models and determining where the dark matter has to be to distort the galaxies in just the right way. Now Dan Coe and collaborators have made an unprecedentedly high-precision map of where the dark matter is (paper here).

This isn’t all about the pretty pictures. We have theoretical predictions about how dark matter should act, and it’s good to compare them to data. Interestingly, the fit to our favorite models is not perfect; this cluster, and a few others like it, are more dense in a central core region than simple theories predict. This is an opportunity to learn something — perhaps clusters started to form earlier in the history of the universe than we thought, or perhaps there’s something new in the physics of dark matter that we have to start taking into account.

But the pretty pictures are certainly a reward in their own right.

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35 Responses to Mapping the Dark Matter

  1. Pingback: Seeing Dark Matter « Space « Science Today: Beyond the Headlines

  2. Peter Fred says:

    @ Valatan asks, “What, pray tell, is a ‘heat-based gravity theory’?” Click Peter Fred above and it will take you to my paper on a “heat-based gravity theory” . There you will find all about how heat mediates the gravitational force.

    On your remarks, “It is not especially hard to solve for appropriate null geodesics of the schwarzschild metric”.

    Why get involved in non-Euclidean geometry if you can explain light bending and secular advance of the perihelion of Mercury the with Newtonian gravitational theory using the Euclidean concept of the jerk. Newton and Einstein were well aware that a Newtonian mass-based gravity theory required the unpalatable idea of action-at-a-distance. Einstein and everybody else thinks that this problem is adequately addressed by GR. But I ask you, “How is mass able to warp space?” This is as much of a”sterile ad hoc formalism” as that held by the Ptolemaics that the earth had some magical ability to cause all the objects in the Heavens to rotate around it in a 24 hour period.

    Since heat and luminosity can easily move through a vacuum, this action-at-a-distance problem disappears with a heat-based gravity theory. Since heat or luminosity is measured in units of power which is intimately related to acceleration, it is not difficult to further interpret just how heat goes about attracting mass. Thus, a heat-based gravity theory cannot be easily considered a “sterile ad hoc formalism”.
    I am “in your face” about a heat-based gravity theory because I am trying to get you to think how dumb a mass-based theory is and how much more logical and “close to experience” a heat-based one is.
    I have experiments that show that heat is attractive. They need to be replicated just as the cosmic acceleration studies had to be replicated because going to a heat based gravity theory is a big change as is the adopting of the idea of cosmic acceleration. ( I hope you click on my name and see the graph in my paper which shows that the onset of the “dimming of the universe” was shortly followed by the onset of “cosmic acceleration”! And if you realize the import of this “coincidence in time of these two cosmic events” you will have stumbled upon another plus for a heat-based gravity theory.

  3. Valatan says:

    You can’t account for both time dialation and special relativity without non-Euclidean curvature–historically, this was Einstein’s motivation far more than the Mercury perehelion precession. The light bending was something that was not even previously predicted that was then observed to verify the original theory. You also need an explanation for why the Hulse pulsar seems to be radiating only in its quadrupole mode if you’re going to chunk GR over the 1919 tests of relativity. That paper I linked cites a large number of high-precision tests for relativity. An argument based around dimensional analysis isn’t extremely convincing in the face of a large number of quantitative predictions.

  4. Peter Fred says:

    You can talk about how non-Euclidean geometry is needed to clear up some points about time-dilation and special relativity and how it is needed to account for the Hulse pulsar results that give some support for gravitational radiation. But non-Euclidean geometry has a hard time accounting for 95 % of the universe that is missing.

    Galaxies are so shaped that luminosity leaving at low angles from their center will be bent and cause luminosity at the edges of a galaxy to fall off as 1/r rather than as 1/r^2.
    If luminosity is attractive as my five experiments indicate, then we have a simple, close-to-experience explanation for the flat rotation curves of galaxies. This could help explain the dark matter problem. At my paper you will also see a graph which shows how shortly after the onset of the “dimming of the universe” the onset of cosmic acceleration occurs. If luminosity is attractive, then we have another simple, close-to-experience explanation for the dark energy problem. With this mass-based theory of General Relativity we have Harvard’s Christopher C. Stubbs saying, “Understanding the nature of Dark Energy is arguably the most profound outstanding problem in contemporary physics.”
    With a heat-based gravity theory this “profound outstanding problem” has a good chance of quietly going away with a very simple explanation.

  5. Valatan says:

    Time dialation and special relativity cannot be reconciled without Non-Euclidean geometry. Having both effects is fundamentally incompatible with a flat spacetime. Both are known to exist to a very, very high precision. If you come up with a theory that explains complicated things without explaining simple things, and then posit a paper with a few plots and very little in the way of actual quantitative predictions, you’re being foolish. There is more evidence for dark matter than luminosity curves. Saying that anamolous galactic rotation curves happen due to heat makes the bullet cluster even more problematic than it is for MOND, where you can at least argue that the self-coupling of the MOND sector might cause decoupling of the lensing matter from the luminous matter.

    That paper by Will has literally hundreds of high-precision experiments. But you’re not interested in any of that. You just want to yell about experiments from 1919 and dark matter. Casually dismissing modern science as ‘you can’t explain 95% of matter’, without even considering that there are a lot of very solid predictions before that statement is made is completely insane. If I’m going to completely rewrite cosmology, for instance, I’d at least THINK about whether or not I’m completely screwing up nucleosynthesis.

    I’m done with this conversation.

  6. Tissa Perera says:

    “Have any friends or colleagues who don’t believe in dark matter? Showing them this should help.”

    Not me Sean. Dark matter is one way to explain things, but that is not the only way. I have published
    an article at my web site to explain it in another way that corroborates the other idea of MOND gravity.
    Dark matter is still not found, and my extra forth space dimension reproduces MOND naturally. As I show, MOND gravity also produces gravitational lensing and therefore can be mapped, not for the presence of Dark matter but because of the presence of a 4th space . Unfortunately, the 4th space is hard to see or detect. So I call it the Dark Space.
    Which is true? Dark Matter or Dark Space? If dark matter is not found(so far not) may be we should start looking for the Dark space?
    /Tissa Perera

  7. John Ramsden says:

    If Dark Matter exists, I reckon it’s backscatter from inside black holes, like mist round a waterfall.

    Some process within black holes (mass inflation possibly?) “measures” momentum with such precision that the Uncertainty Principle means the mass/energy position is uncertain enough that the mass can “leak” back out.

    That would perhaps explain why, despite its significant gravitational effects, it is so damned elusive!

    Mind you, the curious “loop” in one part of that image did give me pause for thought, unless it’s an artifact of the lensing calculation.

    For those not familiar with mass inflation (and references are remarkably sparse – even the mighty Wikipedia had only a place holder last time I checked), it’s a consequence of General Relativity that in certain conditions of highly curved spacetime inside a black hole, when a mere two photons meet a torrent of energy, comparable to all the mass/energy in the observable universe, is released in order to preserve causality. So it’s somewhat analogous a tiny speck of dust under the wheels of an electric train being able to produce a huge spark and a noise like a cannon shot!

    see http://en.wikipedia.org/wiki/Eric_Poisson

  8. John Ramsden says:

    Just a brief clarification of my preceding post – I wasn’t suggesting the mass leaves the interior entirely, in the same sense as Bekenstein-Hawking radiation is emitted from the event horizon (also on account of the Uncertainty Principle, in one of several equivalent interpretations).

    For a significant sized black hole, B-H radiation is mere gnat’s piss compared with the vast torrents of mass inflation that can occur within the hole, and I propose that the “peak probability” of the position (in so far as it comprises particles) remains within the interior with only the tail of the position uncertainty extending considerably outside the event horizon.

    Presumably a similar notion (for what it may be worth) could be expressed using the Uncertainty Principle in terms of other complementary pairs of variables, such as energy and time – If the supposed process regulates or “measures” energy very precisely for example, then one would expect a correspondingly large uncertainty in time, including travelling backwards in time and hence outward from the hole.

    Mind you, I gather antimatter, which is said to be matter travelling backward in time, is affected normally by gravity. So perhaps something doesn’t quite add up with the energy-time version of the idea. Oh well, perhaps I’d better leave the mysteries of dark matter to the experts!

  9. heldervelez says:

    here is a first presentation of a model without no DM, no DE, no space expantion, no BB
    that matches both cosmic and local data. (BBT does not fit local data,…etc,etc..)

    A relativistic time variation of matter/space fits both local and cosmic data
    http://arxiv.org/abs/astro-ph/0208365
    by Alfredo Oliveira.

    In a few words:
    How can we be sure that matter is not shrinking (Length, Mass and Time units vary thru time) instead of space expantion?
    Follow this path and contradictions evade.
    A question of a subtle new interpretation of data.
    Not the simplistic, obvious one that we know full of darkness.

    But the new model do not make directly any enlightment on DM. As BB is not there anymore, the evolution of of the universe at large scale is a new story, at odds with our present assumptions.

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