No. 105: May-Jun 1996
Spiral galaxies are believed to form when gigantic clouds of gas collapse under the pull of gravity to create spinning discs. Further condensations give rise to the billions of stars that make up these immense rotating stellar wheels. Intuitively, one would expect all of the stars in a given galaxy to rotate around the hub in the same direction, like all of the water molecules in a whirlpool. But galaxy NGC4138, 50-million light years away, defies this common-sense expectation.
M. Haynes and colleagues at Cornell have discovered that fully one-fifth of this galaxy's stars are rotating in a direction opposite from the rest. Otherwise, NGC4138 is a well-behaved spiral galaxy, almost a boring one, exhibiting no signs of internal turmoil or past collisions with another galaxy. However, all of the wrong-way stars appear to be youngish. This little clue may lead to some sort of explanation.
(Muir, Hazel; "Counter-Revolutionaries Lurk in Spiral Galaxies," New Scientist, p. 18, March 16, 1996.)
Comment. If all of NGC4138's counterrotating stars did condense from the original spinning gas disc, their large wrong-sign angular momentum would have had to be compensated for by a speed up of all the "right-way" stars.