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No. 36: Nov-Dec 1984

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Galactic Shell Game

Elliptical galaxies are immense assemblages of stars. There may be a trillion stars like our sun in one of these monster galaxies. But it is not the mindboggling number of stars that is anomalous (astronomy dotes on big numbers); rather the anomaly at hand concerns the 11% of the elliptical galaxies that are partly girdled by strange low-luminosity shells.

First reported in 1980, these sharply defined shells seem to be composed of still more stars -- vast ellipsoidal sheets of stars emplaced along the long axis of the elliptical galaxy. Some elliptical galaxies have up to twenty partial shells divided between the two ends of the ellipsoid. What is most intriguing is the fact that the shells are systematically arranged. The closest partial shell will be at one end of the ellipsoid, while the second closest will be at the opposite end. The third closest will be just beyond the first closest, and so on. The shells "interleave" or alternate ends as their distances increase.

If the alternating partial shells of stars belong to the elliptical galaxy (they seem to, agewise), did the elliptical galaxy shoot the first wave out one end and then expel the second wave out the opposite end? Or did the alternating shells form in situ from the primordial gas and dust that made the galaxy? An-other possibility is that a small galaxy collided with the monster elliptical galaxy, and its constituent stars were scattered in regular waves. There is some physical and mathematical support for such a regular scattering of a burst of stars by a dense elliptical mass of target stars.

(Edmunds, M.G.; "Galaxies in Collision," Nature, 311:10, 1984.)

Comment. This star-scattering process reminds one of how electrons are scattered by crystals and other subatomic scattering situations. We may have here another place where quantum mechanics applies in macroscopic nature.

Reference. Galactic "shells" are cataloged in AWO5 in our Stars, Galaxies, Cosmos. To order, visit: here.

Ellipsoidal shells of stars Ellipsoidal shells of stars along the axis of an elliptical galaxy.

From Science Frontiers #36, NOV-DEC 1984. 1984-2000 William R. Corliss