No. 70: Jul-Aug 1990
Blue straggler stars. The stars comprising a star cluster are usually assigned the same age, since it is thought that they were all created at the same time that the cluster was formed. Lurking in many star clusters, however, are brighter, bluer nonconformists called "blue straggler stars." These stars seem to have about twice the mass of the "normal" cluster members, and they appear to be only about one-fifth as old as their compatriots. The motions of the blue stragglers are consistent with those of bona fide cluster members, implying that they are not interlopers or foreground objects. Several explanations have been suggested to explain the presence of blue stragglers. One thought is that they harbor asteroid-size black holes at their cores. So far, all of the profferred explanations have serious flaws.
(Fogg, Martyn J.; "Blue Straggler Stars: A Cosmic Anomaly," The Explorer, 6:4, Spring 1990.)
"A picture book hardly seems a likely source of an astronomical discovery, especially in a world where mysteries of the universe usually tumble from sophisticated electronic instruments attached to huge telescopes. Nevertheless, while recently paging through Exploring the Southern Sky, by G. Madsen and R. West, Walter A. Feibelman (NASA Goddard Space Flight Center) recognized something that had caught his attention decades before. High-resolution photographs of nebulae show large numbers of faint stars surrounded by circular or oval 'empty' regions, giving the impression that the stars are sitting in 'sockets,' a few arc seconds across, swept free of nebulosity."
Feibelman rules out photographic effects, such as halation, but has no ready explanation for socket stars.
M.W. Castelez (Allegheny Observatory) has added to the mystery by pointing out that many socket stars show excess infrared emission. He considers this strong evidence that socket stars are surrounded by shells of dust and may represent an unrecognized stage of stellar evolution.
(Anonymous; "Socket Stars," Sky and Telescope, 79:476, 1990.)