Javier Ballesteros–Paredes1 and Lee Hartmann2
1 Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apdo. Postal 3–72, 58090 Morelia, Michoacán, Mexico (j.ballesteros@astrosmo.unam.mx)
2 Department of Astronomy, University of Michigan, 825, Dennison Building, 500 Church Street, Ann Arbor, MI 48109, USA (lhartm@umich.edu)
Received 2006 May 11
Accepted 2006 October 24
]]> RESUMEN
Discutimos los problemas que presentan algunas estimaciones observacionales que indican tanto tiempos de vida largos para los núcleos densos protoestelares, como grandes dispersiones de las edades de las estrellas asociadas a nubes moleculares. Notamos algunas restricciones observacionales que sugieren que los nucleos densos no tienen tiempos de vida largos antes de colapsar. Para galaxias externas, argumentamos que los anchos de los brazos espirales no implican un proceso de formación estelar largo, ya que la formación de estrellas masivas debe romper las nubes moleculares, mover el material y comprimirlo en otras regiones para producir nuevas regiones de formación estelar. Así, parece inevitable que este proceso cíclico tenga como resultado un período de formación estelar extendido, el cual no representa la longevidad de una nube molecular individual. Argumentamos que la formación estelar rápida indicada observacionalmente es también más fácil de entender teóricamente que el escenario de contracción cuasiestática lenta vía la difusión ambipolar.
ABSTRACT
We discuss problems with some observational estimates indicating long protostellar core lifetimes and large stellar age spreads in molecular clouds. We also point out some additional observational constraints which suggest that protostellar cores do not have long lifetimes before collapsing. For external galaxies, we argue that the widths of spiral arms do not imply a long star–formation process, since the formation of massive stars will disrupt molecular clouds, move material around, compress it in other regions which produce new star–forming clouds. Thus, it seems unavoidable that this cyclical process will result in an extended period of enhanced star formation, which does not represent the survival time of any individual molecular cloud. We argue that the rapid star formation indicated observationally is also easier to understand theoretically than the traditional scenario of slow quasi–static contraction with ambipolar diffusion.
Key Words: STARS: FORMATION — TURBULENCE
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ACKNOWLEDGEMENTS
]]> We thank Tom Dame for providing us the CO data from his Milky Way 2001's survey. This work was supported in part by DGAPA–Universidad Nacional Autónoma de México grant IN110606 to J. B.–P. and NASA grant NAG5–9670 and NAG5–13210 to L. H. This work has made extensive use of NASA's Astrophysics Abstract Data Service and LANL's astro–ph archives.
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