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Markus Feldt

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Collapse of a Molecular Cloud

"collapse.mpg" is the result of a PovRay trace of an SPH (Smoothed Particle Hydrodynamics) simulation. The SPH simulation covers the collapse of a molecular cloud of three solar masses and a radius of 0.6 pc to a protostar and circumventing accretion disk. Actually, particles accreted onto the star are not part of the simulation any more, consequently the star itself doesn't appear in the ray-traced images.

The ray tracer used is PovRay 3.5. The purpose of this tracing is not a physical model that accurately reproduces photometry at various wavelengths or other fancy physical parameters. The idea is to visualize the development of density and size scales during the collapse. No dust model (opacities, size distribution etc.) is assumed for the ray tracer. The colours seen in the image do not correspond to any actual wavelengths. The density calculated by the SPH code is translated into a scattering and absorbing medium. Rayleigh scattering is modelled with scattering coefficients of 0.5 for the "red" channel, 0.7 for the "green" channel, and 0.9 for the "blue" channel. The same coefficients are applied for the absorption. You realize that in priciple it would be possible to adapt to "real physics" quite well at this step.

In the second part of the simulation (during the flight into the cloud), the temperature field delivered by SPH is represented by an emitting medium where total emission is proportional to T^4. The colour of the emission is represented by a map and ranges from black to a bright orange. This is of course purely arbitrary.

The source and the movie are available under GPL, contact me for getting a copy

Numerical Parameters:

Total cloud mass:                3 M_sun
Initial radius:                  0.0616 pc
Mean density:                    2 x 10^-19  g/cm^3
Mean molecular weight:           2.36 g/mol
Initital temperature:            10 K
Initial sound speed:             180 m/s
Jeans mass:                      1.2 M_sun
Mean initial turbulent velocity: 360 m/s (2.0 Mach)

Number of particles:             75,000

Software

SPH Code: 3D Hydrodynamics by W. Benz, I.A. Bonnell, M.R. Bates, R.S. Klessen, B. Lang
Raytracing: PovRay 3.5 (www.povray.org)
MPEG2 encoding: Berkeley MJPEG tools 1.0.6 (mjpeg.sourceforge.net)
M16 background image: NOAO (www.noao.edu/image_gallery)

Hardware

SPH simulation: ANTHILL, 9 x 2 Pentium III (500/700 MHz), SUSE 7.0
Raytracing & MPEG2 encoding: Intel Pentium 4 / 2.0 GHz

Acknowledgements

Usage of the M16 background image courtesy of T.A. Rector (NRAO/AUI/NSF and NOAO/AURA/NSF) and B.A. Wolpa (NOAO/AURA/NSF)

The events depicted in this motion picture are the results of a simulation. Any resemblance to real events in M16, past, present, or future are hopefully not purely coincidential.

No animals were harmed during the making of this movie.

©(2004) mfeldt.pov