Astronomers find 19 more galaxies showing lack of dark matter


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The uncertainty of science: Astronomers have discovered 19 more dwarf galaxies, now totaling 23, that appear to have significant deficits of dark matter.

Of 324 dwarf galaxies analyzed, 19 appear to be missing similarly large stores of dark matter. Those 19 are all within about 500 million light-years of Earth, and five are in or near other groups of galaxies. In those cases, the researchers note, perhaps their galactic neighbors have somehow siphoned off their dark matter. But the remaining 14 are far from other galaxies. Either these oddballs were born different, or some internal machinations such as exploding stars have upset their balance of dark matter and everyday matter, or baryons.

It may not be a case of missing dark matter, says James Bullock, an astrophysicist at the University of California, Irvine. Instead, maybe these dwarf galaxies have clung to their normal matter — or even stolen some — and so “have too many baryons.” Either way, he says, “this is telling us something about the diversity of galaxy formation…. Exactly what that’s telling us, that’s the trick.”

Since we do not know what dark matter is to begin with, finding galaxies lacking it only makes more difficult to create a theory to explain it. Something causes most galaxies to rotate faster than they should, based on their visible mass. What that is remains an unknown.

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11 comments

  • Phill O

    Question: Was not dark matter invented to solve some problem in astrophysics? If there are galaxies which do not require dark matter to explain such deficiencies, is not the very premise of astrophysics not in question?

    Just some thoughts!

  • Scott M.

    Phill O, the main reason to posit dark matter is that on large (galactic) scales stars move much faster than they should. They behave as if under the influence of a larger gravitational force than one would expect after tallying up all of the ‘visible’ matter around them.

    At the moment, the explanation of this is dark matter. Some also postulate some kind of modification to standard gravity at large length scales, but at the moment DM tends to behave like ‘stuff’, as shown in the linked article.

    The biggest problem is that astrophysicists still have no stinkin’ clue what DM is made of.

  • F16 Guy

    Figuring out Dark Matter should be easy. At least according to Sherlock Holmes:

    “How often have I said that when you have excluded the impossible whatever remains, however improbable, must be the truth.”

    (if only that easy !!)

  • wayne

    “There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.
    There is another theory which states that this has already happened.”
    ― Douglas Adams, The Restaurant at the End of the Universe

  • Phill O

    Scott M You are consistent with current theory. However, I am questioning that theory and it’s basis. That is how science develops.

  • brightdark

    Dark matter always reminds me of the classic New Yorker cartoon: https://www.flickr.com/photos/jpallan/4633000725

  • Edward

    Are the dwarf galaxies moving around the larger galaxies as though the larger galaxies have dark matter?

    Astronomers keep telling us that dark matter is necessary for most galaxies to rotate in the way that they do, but I have yet to hear them talk about how all that extra mass in each galaxy is proven by the motions of the galaxies around them.

    Phill O asked: “Was not dark matter invented to solve some problem in astrophysics? If there are galaxies which do not require dark matter to explain such deficiencies, is not the very premise of astrophysics not in question?

    Yes, to the first question, and to the second: this is why one astronomers said, “This new class of galaxy is straining our ability to explain all galaxies in one cohesive framework.

    I keep wondering whether what we have defined as dark matter and dark energy may actually be two forces that we do not detect on our scale.

    On a subatomic scale, the strong force and the weak force are dominant, but gravity has virtually no effect. What if there are two forces that have an effect on galactic or universal scales but not on planetary scales? Would we misinterpret these forces as undetected matter and undetected energy?

  • Edward: Your last paragraph is exactly the premise on which the theorists who developed MOND (Modified Newtonian dynamics) base their work. They look to see if modifying the laws of gravity (and other basic physics) on very large scales can explain these phenomenon. So far, they have failed, but that doesn’t mean this isn’t the answer.

  • John

    Nobody really understands black holes. You often read that at the singularity the “physics break down” or “calculations give infinity or nonsense answers” or even “time ends”.

    Maybe when gravity collapses space time there’s a gravitational effect outside the singularity, and far away at that. I call it “Conservation of Gravity”. CoG: Gravity tears a hole in the universe here at this single point, and you get gravity effects everywhere in the now broken continuum.

    So my crackpot theory says that the dark matter poor galaxies are just black hole deficient dwarfs. Throw a super massive black hole in the center of one, and you’ll see it spin right up.

    You wont ever see a large galaxy without dark matter because they all have supermassive black holes at the center, or at least a population of other black holes.

  • wayne

    TEDxWarwick – Sir Roger Penrose –
    “Space-Time Geometry and a New Cosmology”
    2011
    https://youtu.be/oBkOYQ02chs
    21:43

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