Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                               2019 November 5

                     Spiral Galaxies Spinning Super-Fast
      Image Credit: Top row: NASA, ESA, Hubble, P. Ogle & J. DePasquale
                                  (STScI);
              Bottom row: SDSS, P. Ogle & J. DePasquale (STScI)

   Explanation: Why are these galaxies spinning so fast? If you estimated
   each spiral's mass by how much light it emits, their fast rotations
   should break them apart. The leading hypothesis as to why these
   galaxies don't break apart is dark matter -- mass so dark we can't see
   it. But these galaxies are even out-spinning this break-up limit --
   they are the fastest rotating disk galaxies known. It is therefore
   further hypothesized that their dark matter halos are so massive -- and
   their spins so fast -- that it is harder for them to form stars than
   regular spirals. If so, then these galaxies may be among the most
   massive spirals possible. Further study of surprising super-spirals
   like these will continue, likely including observations taken by NASA's
   James Webb Space Telescope scheduled for launch in 2021.

                       Tomorrow's picture: open space
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                             & Michigan Tech. U.

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