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posted by Fnord666 on Saturday March 18 2017, @09:19AM   Printer-friendly
from the where-did-I-put-my-keys dept.

John Timmer authored an Ars Technica story reporting on research published on 15 March 2017, which appears to show that as we look farther back in time, galaxies had less dark matter.

From the Ars Technica article:

One of the earliest indications of the existence of dark matter came from an examination of the rotation of nearby galaxies. The study showed that stars orbit the galaxy at speeds that indicate there's more mass there than the visible matter would indicate. Now, researchers have taken this analysis back in time, to a period when the Universe was only a couple billion years old, and the ancestors of today's large galaxies were forming stars at a rapid clip.

Oddly, the researchers find no need for dark matter to explain the rotation of these early galaxies. While there are a number of plausible explanations for dark matter's absence at this early stage of galaxy formation, it does suggest our models of the early Universe could use some refining.

[...]

In fact, it's thought that dark matter catalyzed the formation of most galaxies. Simulations suggest that gravity draws dark matter into a web of filaments, and galaxy formation occurs primarily at the sites where these filaments meet. This explains why most galaxies we see today exist in clusters. Given this model, it's simple to assume that the condensation of dark matter into galactic disks preceded or ran in parallel with the production of the visible portion of the galaxies.

The new data would suggest otherwise. The authors took advantage of existing survey data to identify six large early galaxies that don't appear to have recently undergone a merger and have an abundance of stars. They are thought to be the precursors of galaxies such as our own and are already big enough to show a clean rotation curve. Their rotation was then measured using the red and blue shifts of light emitted by hydrogen, based on observations with the Very Large Telescope.

[...]

The authors of the new paper see a number of possible explanations. One is that the early galaxies are very gas-rich, and these clouds of gas can experience local instabilities or collisions. This could cause the regular matter in the inner galaxy to compact, resulting in a normal-matter-dominated portion of the galaxy. The other possibility is that rather than forming the seeds of galaxies, dark matter starts off rather diffuse and takes time to form a disk-like structure that mirrors that of the visible galaxy. Either of these would explain the apparent matter dominance.

This doesn't turn current theories of dark matter on their heads, but it may provide avenues for research in better understanding both dark matter and large-scale cosmic structures.

Referenced Paper: Strongly baryon-dominated disk galaxies at the peak of galaxyformation ten billion years ago (Nature, 2017. DOI: 10.1038/nature21685).


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  • (Score: 3, Insightful) by opinionated_science on Saturday March 18 2017, @01:19PM (5 children)

    by opinionated_science (4031) on Saturday March 18 2017, @01:19PM (#480826)

    https://physicsfromtheedge.blogspot.com [blogspot.com]

    This guy's idea - MiHSC , modified inertia. Makes a great deal more sense and is less handy wavy...

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  • (Score: 0) by Anonymous Coward on Saturday March 18 2017, @01:39PM

    by Anonymous Coward on Saturday March 18 2017, @01:39PM (#480831)

    No emdrive, no sale.

  • (Score: 0) by Anonymous Coward on Sunday March 19 2017, @02:35AM

    by Anonymous Coward on Sunday March 19 2017, @02:35AM (#481009)
    McCulloch has a number of papers on this idea, which do not seem to have such high impact. One such paper from 2012, “Testing quantised inertia on galactic scales [google.com]” has 13 citations, only three of which are not by his own papers or papers co-authored by him. Another paper from 2010, “Minimum accelerations from quantised inertia [google.com]” has 15 citations, but only two of which were self-citations. It seems his most-cited work is his paper on the Pioneer anomaly [wikipedia.org], with 41 citations [google.com], but his particular explanation for it has been discredited and a much more prosaic explanation for the phenomenon has been identified. It seems that real astrophysicists and cosmologists who likely know more than you or I don’t seem to think his ideas really do make a great deal more sense and are less handy wavy and most of all agree with observational data, enough to cite his work extensively.
  • (Score: 2) by maxwell demon on Sunday March 19 2017, @08:15AM (2 children)

    by maxwell demon (1608) on Sunday March 19 2017, @08:15AM (#481085) Journal

    How exactly does this address the issue in my comment?

    --
    The Tao of math: The numbers you can count are not the real numbers.
    • (Score: 2) by opinionated_science on Sunday March 19 2017, @01:51PM (1 child)

      by opinionated_science (4031) on Sunday March 19 2017, @01:51PM (#481132)

      it proposes a new model of gravitation based upon "quantised inertia" (an interesting idea if nothing else) , that accounts for the distribution of visible mass in the universe.

      That may add some value to "avenues for research in better understanding both dark matter and large-scale cosmic structures."

      • (Score: 2) by maxwell demon on Sunday March 19 2017, @02:11PM

        by maxwell demon (1608) on Sunday March 19 2017, @02:11PM (#481136) Journal

        Please no general blah-blah. Please tell me how that theory deals with the specific issue I described in my comment.

        --
        The Tao of math: The numbers you can count are not the real numbers.