The stars that shouldn’t be there: (Mostly) dynamical solutions to existential paradoxes

Hagai Perets

April 11, 2011

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Abstract: Some stars are found in the wrong place and/or at the wrong time. Apparently young stars, so called blue stragglers, are found in very old stellar clusters. The environment near the massive black hole (MBH) in the Galactic center is very hostile to star formation, yet newly formed stars are found very close to the MBH. The galactic halo is thought to be composed of very old stars, yet young stars are observed in such environment too. Similarly supernovae supposedly produced from the core collapse of massive young stars are found in galactic halos and in elliptical galaxies, where such young stars should not exist. In my talk I will discuss such ‘existential’ paradoxes of youth and suggest (mostly) dynamical solutions which can explain the origin of such out of place/time stars. As I will show the solutions to these various puzzles could have important implications for our understanding of various issues, from missing components in current population synthesis studies, stellar dynamics in galactic nuclei and dense stellar systems, measuring the dark component of the galaxy and the chemical composition of the universe.