Home People MRB Cluster Hydro Star Cluster 4

The Dependence of Star Cluster Formation on the Initial `Turbulent' Power Spectrum

Matthew R. Bate

This was the four large-scale calculation to be performed. The initial conditions were identical to those in the original calculation, except that the `turbulent' velocity field imposed on the cloud had a different power spectrum P(k) \propto k-6 which has more power in large scale gas motions than the other calculations (which used P(k) \propto k-4). The aim was to determine whether changes in the initial velocity field (which is somewhat arbitrary because the initial conditions in molecular clouds are not well understood) had an impact on the star formation or not. It is found that the stellar mass distribution (the so-called initial mass function, IMF) was statistically identical to the IMF from the original calculation showing that the initial power spectrum is unimportant.


Copyright: The material on this page is the property of Matthew Bate. Any of my pictures and animations may be used freely for non-profit purposes (such as during scientific talks) as long as appropriate credit is given wherever they appear. Permission must be obtained from me before using them for any other purpose (e.g. pictures for publication in books).

Simulation & visualisation by Matthew Bate, University of Exeter unless stated otherwise.

Notes on formats:
Quicktime: Plays directly in Powerpoint only on an Apple computer. Can be played under Windows by downloading the FREE Quicktime player from Apple. Can be played under Unix/Linux using xanim.
MPEG-4: Can be played using Windows Media Player or Quicktime player. Small file size.

  Movie comparing the evolutions of the original calculation (calculation 1; left) and the cloud with a different initial turbulent power spectrum (calculation 4; right).

Available formats for 115 second animation (15 frames/sec):
Quicktime (27MB, high quality)

  Movie comparing the evolutions of the low-metallicity cloud (calculation 3; left) and the cloud with a different initial turbulent power spectrum (calculation 4; right).

Available formats for 111 second animation (15 frames/sec):
MPEG-4 (27MB, medium quality)
Quicktime (31MB, high quality)

Technical Details

The calculation models the collapse and fragmentation of a 50 solar mass molecular cloud that is 0.375 pc in diameter (approximately 1.2 light-years). At the initial temperature of 10 K with a mean molecular weight of 2.46, this results in an thermal Jeans mass of 1 solar mass. The free-fall time of the cloud is 190,000 years and the simulation covers 266,000 years.

The cloud is given an initial supersonic `turbulent' velocity field in the same manner as Ostriker, Stone & Gammie (2001). We generate a divergence-free random Gaussian velocity field with a power spectrum P(k) \propto k-6, where k is the wave-number. This power spectrum is much steeper than the Kolmogorov spectrum, P(k)\propto k11/3 and the Burgers supersonic turbulence power spectrum.

The calculation was performed using a parallel three-dimensional smoothed particle hydrodynamics (SPH) code with 3.5 million particles on the United Kingdom Astrophysical Fluids Facility (UKAFF). It took approximately 80000 CPU hours running on up to 64 processors. The SPH code was parallelised using OpenMP by M. Bate. The code uses sink particles (Bate, Bonnell & Price 1995) to model condensed objects (i.e. the stars and brown dwarfs). Sink particles are point masses that accrete bound gas that comes within a specified radius of them. This accretion radius is to set 5 AU. Thus, the calculation resolves circumstellar discs with radii down to approximately 10 AU. Binary systems are followed to separations as small as 1 AU.

Refereed Scientific Papers

"The dependence of star formation on initial conditions and molecular cloud structure" Bate, M. R., 2009, MNRAS, 397, 232. ( Local PDF preprint or preprint from astro-ph/0905.3562 )

High Resolution Still Images and Commentary

High resolution, unannotated (1800x1800 pixel) versions that are suitable for publication are available on request by emailing Matthew Bate at: mbate @ astro.ex.ac.uk

Click on the images below to view medium resolution, annotated (600x600 pixel) versions.

Copyright: Matthew Bate, University of Exeter.

0 yr: We begin with such a gas cloud, 2.6 light-years across, and containing 500 times the mass of the Sun. The images measure 1 pc (3.2 lightyears across).   38,000 yr: Clouds of interstellar gas are seen to be very turbulent with supersonic motions.   76,000 yr: As the calculation proceeds, the turbulent motions in the cloud form shock waves that slowly damp the supersonic motions.  
114,000 yr: When enough energy has been lost in some regions of the simulation, gravity can pull the gas together to form dense "cores".   152,000 yr.   209,000 yr: The formation of stars and brown dwarfs begins in the dense cores.  
228,000 yr.   247,000 yr: As the stars and brown dwarfs interact with each other, many are ejected from the cloud.   266,000 yr: The cloud and star cluster at the end of simulation. Some stars and brown dwarfs have been ejected to large distances from the regions of dense gas in which the star formation occurs.  
228,000 yr: Close up view in of the star formation in the top right-hand core.   247,000 yr.   266,000 yr.  
228,000 yr: Close up view in of the star formation in the lower left-hand core.   247,000 yr.   266,000 yr.  

Validate   Link-check © Copyright & disclaimer Privacy & cookies Share