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Space Science

Hubble Builds 3D Dark Matter Map 177

astroengine writes "Dark matter can't be spotted directly because it doesn't interact with electromagnetic radiation (i.e. it doesn't emit any radiation and reflects no light). However, its gravitational influence on space-time can bend light from its otherwise straight path (a phenomenon known as 'lensing'). Using a sophisticated algorithm to scan a comprehensive Hubble Space Telescope survey of the cosmos, astronomers have plotted a map of 'weak lensing' events. Combining this with red shift measurements from ground-based observatories, they've produced a strikingly colorful 3D map of the structure of dark matter."
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Hubble Builds 3D Dark Matter Map

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  • by dakameleon ( 1126377 ) on Sunday March 28, 2010 @08:50PM (#31652030)

    From TFA, the closest hint we get to the 3D nature:

    By combining the Hubble observations of gravitational lenses with spectroscopic red shift observations from telescopes on Earth, the 3D location of clumps of mass (dark matter, galaxies, black holes etc.) can be found. In this case, the white, cyan, and green regions are closer to Earth than those indicated in orange and red.

    but yes, the rest is pretty awful... it's just a starfield without any context with blotches of colour randomly scattered over it.

  • by Anonymous Coward on Sunday March 28, 2010 @09:06PM (#31652114)

    X = X
    Y = Y
    Z = RGB

    FTFA: "the white, cyan, and green regions are closer to Earth than those indicated in orange and red."

  • by Kratisto ( 1080113 ) on Sunday March 28, 2010 @09:15PM (#31652160)
    You could do it based on movement speeds. Things in the background of an image move slower than those in the midground when you change your position--If the thing in the background, a galaxy or something, moves in a strange way, then you can be sure it's being lensed. I'm not sure if the Earth moves enough for this to be useful, though, given the scale.
  • by Anonymous Coward on Sunday March 28, 2010 @09:33PM (#31652278)

    Sorta. As the earth goes around the sun, we do in fact get enough parallax to determine the distance to nearby stars. On the galactic scale, though, this doesn't work. The way they find lensing artifacts is that lensing doesn't just skew a single flat image of what we see, it might bend the same light source so it comes at us from different angles, producing multiple images of a single event. Something like this: http://en.wikipedia.org/wiki/Einstein_Cross

    If they have good enough images with spectral plots for each pixel (which if they are using redshift to determine distance, they must have), I could see an algorithm being able to pick out which images are mirages, and therefore where the lensing matter must be.

  • by Chris Burke ( 6130 ) on Sunday March 28, 2010 @09:42PM (#31652340) Homepage

    ...but I fail to see the 3D that was promised by TFA.

    Yeah sadly it's the data that's 3D, not the presentation. They located the dark matter in three dimensions, the 3rd being distance according to red shift which is how it's colored. I can see how it's hard to find the explanation, too, what with them breaking up the story every couple paragraphs with a giant bold link to something else. I thought those were different news items at first!

    Bad presentation in the article aside, this is pretty amazing work. What a phenomenal instrument we have in Hubble.

    The article on the the Hubble site [spacetelescope.org], while similarly lacking a good explanation for the image, actually talks about dark energy more than dark matter. Apparently this data also indicates a universe expanding outward from every point, corroborating that theory, along with some GR experimental validation as well. Not bad for a days work.

  • by Colonel Korn ( 1258968 ) on Sunday March 28, 2010 @09:43PM (#31652348)

    ...how they know it’s lensing, and that the stars aren’t just positioned like that?

    Sounds to me like you could never prove, which one it really is, until you fly behind that “dark matter”. (To me still a imaginary excuse, based on the arrogance of not being able to admit that the math is wrong, but instead calling the universe wrong! ^^ [But a good {and compact!} explanation will of course change my mind.])

    When you see multiple images of the same object, it's lensing. This is, in fact, how gravitational lensing was first discovered. Check out this great wikipedia image of the effect: http://en.wikipedia.org/wiki/File:Einstein_cross.jpg [wikipedia.org]. This is actually called strong lensing. TFA discusses weak lensing, which is a much smaller effect. That's detected by looking at very distant galaxies. Lensing changes the shape of galaxies such that there is a preferred orientation. If this orientation is statistically significant, i.e., too many galaxies are stretched in the same direction to be caused by normal physics, then it tells us that the weirdness is likely caused by lensing. Thanks to Hubble's ability to paint an incredibly dense picture of background galaxies, our statistics are based on a huge number of samples and we can trust them pretty thoroughly.

    Awesome, right?

  • by Abcd1234 ( 188840 ) on Sunday March 28, 2010 @09:44PM (#31652356) Homepage

    ...especially when you consider it's a picture of something that very possibly doesn't even exist.

    It exists. Educate [wikipedia.org] yourself [wikipedia.org].

  • by Anonymous Coward on Sunday March 28, 2010 @09:57PM (#31652422)

    Thanks. It's worth noting that the Bullet Cluster results you linked to are only the most recent development in dark matter's nearly 80 year history:

    1933 - Zwicky studies the Coma cluster of galaxies and is surprised to find that these galaxies are orbiting each other much faster than he predicted based on their visible mass. He proposes that each galaxy actually contains much more mass than is visible.

    1959 - Measurements of galactic rotational velocities conflict with expected velocities based on the amount of matter observed to be present. The dark matter concept proposed by Zwicky is found to solve this problem too.

    1970s - Big Bang nucleosynthesis has trouble reconciling observations of high deuterium density with the expansion rate of the universe. Non-baryonic dark matter solves this problem as well.

    At this point, dark matter was simply an hypothesis. MOdified Newtonian Dynamics (MOND [umd.edu]) was another hypothesis with equal weight. But then in 2006 measurements of the Bullet Cluster supported the dark matter hypothesis over the MOND hypothesis.

    Simultaneously, WMAP [wikipedia.org] (2001-present) measured the microwave background radiation and independently confirmed the existence of dark matter. It also revealed an even larger amount of "dark energy" which confirmed the 1998 discovery [arxiv.org] that the expansion of the universe is accelerating.

  • by jeff4747 ( 256583 ) on Sunday March 28, 2010 @10:08PM (#31652496)

    how does this map distinguish dark matter from other sources of lensing?

    IANAAstrophysicist, but my understanding is that a point source, such as a black hole, would create a strong lensing effect. These observations are of a weak lensing effect that indicates a diffuse source of gravity.

    By stating Dark matter has no interaction with electromagnetic radiation clearly contradicts the support that it also bends light.

    The dark matter doesn't bend light. The gravity from the dark matter bends light.

  • by Abcd1234 ( 188840 ) on Sunday March 28, 2010 @10:34PM (#31652678) Homepage

    Actually, it does exist. Frankly, I'm fucking sick of posting the same links over and over, so why don't you just go to Wikipedia and read about the Bullet Cluster. There is simply no question, now, even among MOND proponents: there is weakly interacting matter out there, and we have no idea what it is.

  • by largesnike ( 762544 ) on Sunday March 28, 2010 @10:47PM (#31652736)
    I know this is slashdot, but you could try RTFA that that article links to...

    "I'll note: this has nothing to do with dark matter. As it happens, 90% of the matter in the Universe is in a form that emits no light, but affects other matter through gravity. We know it exists ... locally, in nearby galaxies and clusters of galaxies, too. This new result doesn't affect that, since the now un-hidden galaxies are very far away, like many billions of light years away. They can't possibly affect nearby galaxies, so they don't account for dark matter."

  • by carlzum ( 832868 ) on Sunday March 28, 2010 @10:52PM (#31652754)
    There are 3D dark matter maps [wikimedia.org] out there. This map provides some context for someone on Earth.

    In this case, the white, cyan, and green regions are closer to Earth than those indicated in orange and red.

    The image doesn't really help me visualize the concept, but it attracted me to the article. That's probably the intent of these kind of images, grab people's attention and explain the findings when they want to know what the hell they're looking at.

  • by TapeCutter ( 624760 ) * on Monday March 29, 2010 @12:44AM (#31653352) Journal
    "These theories just happen to be the best explanations for what scientists observe."

    Exactly! Dark matter and dark energy are just tags for unexplained phenomena that appear to have similar properties to matter and energy. They are not simply mathematical entities, they are phenomena that can be observed but cannot (yet) be explained with our mathematical models. This is no different to any other physics, Newton didn't discover gravity he discovered it could be described with maths.
  • by Anonymous Coward on Monday March 29, 2010 @02:31AM (#31653930)

    Yes. That's called parallax. Is measurable only in stars which are close by.

          * good out to 100 pc
            * only get 10% distances out to a few parsecs.
            * only a few hundred stars are this close


  • by nadaou ( 535365 ) on Monday March 29, 2010 @07:38AM (#31655262) Homepage

    By stating Dark matter has no interaction with electromagnetic radiation clearly contradicts the support that it also bends light.

    The dark matter doesn't bend light. The gravity from the dark matter bends light.

    or put another way, the dark matter doesn't bend light -- it bends space. (!)

  • by b4dc0d3r ( 1268512 ) on Monday March 29, 2010 @12:35PM (#31658712)

    The article dated "March 26, 2010":
    http://news.discovery.com/space/hubble-3d-map-universe-dark-matter.html [discovery.com]
    has a source dated 25-Mar-2010::
    http://www.spacetelescope.org/news/html/heic1005.html [spacetelescope.org]
    with this quote which explains everything:

    A new study led by European scientists presents the most comprehensive analysis of data from the most ambitious survey ever undertaken by the NASA/ESA Hubble Space Telescope. These researchers have, for the first time ever, used Hubble data to probe the effects of the natural gravitational "weak lenses" in space and characterise the expansion of the Universe.

    The data was old, the analysis and imaging is new.

    The 'Links' at the bottom include the new paper, and the old study. The old press release dated "7-errNoSuchMonth-2007":
    "News Release heic0701 - First 3D map of the Universe's Dark Matter scaffolding"
    http://www.spacetelescope.org/news/html/heic0701.html [spacetelescope.org]

    Is the one described your original article:
    http://news.bbc.co.uk/2/hi/science/nature/6235751.stm [bbc.co.uk]

The tree of research must from time to time be refreshed with the blood of bean counters. -- Alan Kay