March 4, 2006 | David F. Coppedge

Spiral Galaxies Wind Up Into Blurs In Short Cosmological Time

Cosmic billions of years have received another challenge.

Sky and Telescope reported on a announcement by Michael R. Merrifield (University of Nottingham, England), Richard J. Rand and Sharon E. Meidt (University of New Mexico) in Monthly Notices of the Royal Astronomical Society that they measured the velocity of gases in the spiral galaxy, M77, and found that they behave just as you would expect: gases toward the center of the galaxy are orbiting faster than gases farther out. “Billions of years” cosmology requires that the spiral structure of galaxies be caused by something other than simple orbital mechanics, otherwise the spirals would blur in a cosmologically short time.

Merrifield and his colleagues derived new formulas and applied them to measurements of M77’s carbon-monoxide-laced gas clouds (carbon monoxide molecules emit finely tuned radio waves, allowing astronomers to precisely measure the positions and line-of-sight velocities of interstellar matter). Spiral-shaped wave patterns that are just 3,000 light-years (20 arcseconds) from the galaxy’s center whirl around the core three times as often as those 6,000 light-years out, says the team – all but guaranteeing that the galaxy’s bright inner pinwheel is destined to wind itself up into an amorphous disk. “If this result turns out to apply commonly to other galaxies,” the scientists write, “then intergalactic travelers would be well advised not to use the morphology of spiral structure to identify their homes.”   [Emphasis added in all quotes.]

The scientific community is not so easily persuaded:

Bruce G. Elmegreen (IBM Thomas J. Watson Research Center) cautions that the composition of M77’s interstellar clouds may differ from place to place, possibly fooling Merrifield and his collaborators into thinking that the innermost parts of the galaxy’s spiral pattern will outrace the outer parts after a few laps around the track. And while M77’s inferred identity as a quick-change artist doesn’t surprise John Kormendy (University of Texas, Austin), he doubts that M77’s subtle inner spiral can shed much light on the longevity of simple but bold spirals seen in prominently barred galaxies like NGC 1300 and in closely interacting ones like M51.

Merrifield and his colleagues have shown with empirical evidence that spiral galaxies are doing exactly what they look like they are doing: spinning in an ever tightening wind-up that will, in a short time cosmologically, completely erase their spiral structure. This is anathema to astronomers such as Elmegreen and Kormendy who must at all costs support the 13 billion year old age of the universe. Elmegreen and Kormendy had no evidence of their own to refute Merrifield, and so resorted to attacking the quality of Merrifield’s data.

Since the 1930s when this problem first surfaced, astronomers have had to come up with fanciful explanations for how the spiral structures remain in place for billions of years. Density waves are the current favorite: we are asked to believe that the spiral arms we see are just waves of higher density that propagate through the galaxy in spiral patterns, creating new stars as they progress. Computer modeling this theory has been challenging.  The models must be creatively tuned to produce the observed spiral structures (see Russell Humphreys’ point #1 for young age on AiG).

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