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Re: Galaxies And Age Of Lone Stars

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Posted by Bruce Jensen/">Bruce Jensen on May 27, 1997 11:29:07 UTC

: Has anyone ever studied whether individual stars are older as a group than stars associated with a galaxy or star group? It just occurred to me in looking at the photograph I have as my computer wallpaper (AAT55) that a spinning galaxy is like the game of crack the whip. In the game the last person tends to get spun off from the twisitng line. I wonder if individual stars have been spun off from the ends of galaxy arms. If so, they might be older in general than the stars in galaxies.

Sara - until recently, nobody had any good evidence of stars residing outside of galaxies per se, and many didn't believe that stars were there. Recently, however, individual stars were discovered apparently floating by themselves in the midst of the nyriad of galaxies in the Vorgo Cluster of Galaxies, some 50 million LY away. A few hundred red giants were found, floating between the galaxies as though not associated with any one of them but probably in the grip of the cluster as a whole, providing the first real evidence of this phenomena. Although only several hundred were found, these were of the largest and brightest red giant type; trillions of stars of varying classes are theorized to reside in intergalactic space within that cluster that are smaller and dimmer. The presence of red giant stars suggests that the stars themselves are probably old and ready to give up the ghost as either supernovae or white dwarves, but the remainder of unseen stars may be of many ages. Your comment about crack the whip is interesting, but it probably doesn't work that way. Although a galaxy looks like a whip, it is actually a system of mass in orbit. The stars close in orbit very quickly around the center of mass, while the stars on the fringes orbit much more slowly. This is a simplification of galactic dynamics, because spiral arms apparently do not wrap themselves up and are maintained in some wave-like system, but for practical purposes a galaxy is pretty well coherent system. Stars in between probably are the result of galactic collisions rather than any internal "whipping" of outlying members. One more thing that you may want to consider is that stars within globular clusters, while being generally the oldest of stars (in many cases probably spanning back to the earliest days of the universe), are also the groupings that follow the most unusual orbits around their host galaxies, at least in the case of spirals. The GC's around the Milky Way, for example, surround the central mass like an extended halo, reminiscent of the large elliptical galaxies, instead of swirling around and contributing to the spiral; they also follow their own elliptical orbits around the center, swingning through the disc of the spiral many times as they orbit. A very few of these GCs were, at least until recently, considered to be strong candidates for intergalactic renegades, wandering between the galaxies and never really hooking up with a single one. There is still one of these out in the constellation Lynx, the "intergalactic wanderer," which is so far away and moving so fast that it may escape the Milky Way altogether. Thus, in one limited sense, the "intergalactic stars" may, as a group, be older by proportion than the stars of the host galaxies. I'll stop now, and let someone else get a word in edgewise...BJ

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