Galaxy Orbits Betray Neatnik Universe

By Bill Andrews | July 23, 2014 8:00 am
The Andromeda Galaxy turns out not to be unusual in the fact that its dwarf galaxies orbit within an orderly circular plain. Credit: NASA/JPL-Caltech

The Andromeda Galaxy turns out not to be unusual in the fact that its dwarf galaxies orbit within an orderly circular plain. Credit: NASA/JPL-Caltech

Usually, the progress of science leads to greater complexity — alas, Earth isn’t the only world; no, electrons aren’t tiny little balls; unfortunately, germs aren’t all good or all bad . But once in a while, scientists discover the universe likes a little order, too: Astronomers have just found out the hordes of dwarf galaxies that orbit big ones tend to do so within a nice, well-defined disk. Now the only question is, why?

Grappling with Galaxies

It’s a great big universe out there, filled with hundreds of billions of galaxies of different sizes. Most are relatively small dwarf galaxies, which tend to cluster around bigger and more massive galaxies. Computer models had long predicted that the little ones should orbit chaotically around the big ones, swarming like flies in random paths.

Our own Milky Way Galaxy appeared to be a bit unusual, since it was clear most of our small companion galaxies orbited a little more neatly, in a flat, disk-like plane. Astronomers had just chalked that up to coincidence, but then last year a team of researchers announced that the dwarf galaxies around the nearby Andromeda Galaxy (M31) all orbited within a single large thin disk, too.

Intrigued, some of those team members wanted to find out if the Milky Way and Andromeda galaxies were outliers, or if other large galaxies also kept their dwarfs in line. After analyzing the velocities of smaller companions in 380 galaxy systems from the Sloan Digital Sky Survey (a huge collection of galactic data), they had their answer: orderly disks seemed to be the norm. As their Nature paper puts it, “We have found that the average giant galaxy in the SDSS is consistent with our M31 template.”

Orderly Mystery

Again, this goes against expectations, so it’s not clear yet why smaller galaxies should prefer to orbit within well-defined disks. It could be that the current models and simulations aren’t powerful enough yet, and can’t account for all the subtle factors at play in a galaxy’s orbit. Or, it could mean there’s some essential knowledge gap in our understanding of the cosmos, from something unexpected influences in gas flow patterns to something as fundamental as misunderstanding gravity itself. Only time will tell what brings about this unexpected order.


CATEGORIZED UNDER: Space & Physics, top posts
  • Robert MacKay

    You mean to say that our knowledge level and the computer models we build using that knowledge may not be accurate as it relates to Galaxies – imagine that ! We have been truly studying galaxies for maybe 100 years at best and the author thinks that we should be surprised that our knowledge is still incomplete ? We are absolute infants with regard to our cosmic knowledge – why is this surprising at all ?

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  • m12345

    I dont understand, this knowledge is well-known, has been for 20+ years. Is there something wrong with science today?

    All mass will clump, this is proven, as mass moves together there are inherent anomalies in the distributuion, so it starts rotating, as soon as the rotation is started, more mass adds to that rotation as it gets slowly drawn into the disk and equalises in position.

    There may well be differences at galactic scale, but this article is deliberately not invoking that nasty term dark matter, which has so far in every single experiment been proven to not exist.

    Also science is about simplification, with a nice neat formula. You could say the formula of understanding or maths if you prefer.

    • Drchuck Ll

      Actually, the observations strongly suggest dark matter exists. Just because it has not been found yet proves nothing. Whatever is found will be called dark matter even though we have no idea what it is. Science is not easy and is certainly not simple, as I’m sure Einstein could explain. Unfortunately, I would not understand his explanation.

    • Artor

      “…dark matter, which has so far in every single experiment been proven to not exist.”
      [citation needed]
      Which experiments would these be? Got links? Your statement about “proven” show you have a sketchy knowledge of science. You might want to read up a little.

  • gregorylent

    mystics have known this for centuries .. and also understand that there are multiple universes


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