CfA Colloquium Schedule Spring 2004
 4 March 2004

4 March 2004

Speaker: Ralph Pudritz (McMaster University, Canada)

Title: The formation of star clusters - 3D simulations of hydrodynamic turbulence in self-gravitating gas

Abstract: Two fundamental properties of stars that must be explained by a complete theory of star formation are the distributions of their initial masses (the initial mass function - or IMF) and initial angular momenta (the inital angular momentum function - or IAMF). Observations show that the mass spectrum of dense cores in turbulent, cluster forming clumps within molecular clouds have an IMF-like mass spectrum suggesting that the origin of the IMF lies in the physical process that produces the molecular cloud cores. In this talk I will focus on a relatively new theoretical picture for star formation which predicts that turbulence is the primary driver for the formation of the IMF. I will review the basic ideas in this "turbulent fragmentation" picture, and then report the results of recent 3D simulations of dense molecular clumps carried out by Tilley and Pudritz (2004). We find that complex structure and stellar clusters are formed if the damping time of the turbulence is longer than the gravitational free-fall time in the region. We find a range of properties for molecular cloud cores - some are almost thermal and have density profiles resembling the classical "Bonner-Ebert" self-gravitating sphere solutions, while others have significant turbulence within them and have a 1/r radial density profile reminiscent of logatropic cores. The mass spectra of the simulations reproduce the IMF well while a broad IAMF results from the distribution of spins that cores inherit from the fragmented oblique shocks out of which form. The simulations reproduce many of the observed properties of molecular cloud cores. Finally, I will also show new collapse simulations (that include molecular cooling) of such cores into protostellar disks - the percusors of proplanetary disks - that we follow using the FLASH, Adaptive Mesh Refinement (AMR) code.

References for students:

  1. Pudritz, Science, 295, p. 68
  2. Vazquez-Semadeni et al, Protostars and Planet IV 2000, p. 3
  3. Padoan and Nordlund 2002, ApJ, 576, p. 227
  4. Truelove et al 1998, ApJ 495, p. 821


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