Collaboration on Core Collapse from Germany to LSU

An initially rapidly rotating Maclaurin spheroid with \beta=|T/W|> 0.27 undergoes dynamical instability toward m=2 fundamental mode(barmode), where T and W denote the rotational and gravitaional potential energy of the object respectively. Classical studies shows that the critical limit \beta = 0.27 is mostly independent of the compressibility and the rotational law or the angular momentum distribution of the star. However, recent investigations (Centrella et al., 2001; Shibata et al. 2002) shows that in some extremly differential rotating case, the critical limit might drop to a lower value.

On the other hand, the core collapse of a massive star can give birth to a differentially rotating neutron star, therefore it would be very interesting to see if a newly-born neutron star will deforme into a bar shape although it only has a \beta value much lower than the critical limit.

Here, we used LSU hydro code FLOWER (Motl, Tohline, Frank 2001) to evolve one model from the core collapse simulations of Christian Ott from Albert Einstein Institute in Germany.

Movies for the core collapse simulation
Resolution	# of processors	computer	plots	movies	comments
98194128	32Pentium 4	LSU Superhelix & AEI Peyote	\beta, angmom, J22_1, strain, modes, final \omega profile	side view, top view, top view II, phase angle of m=1	to be continued

In the above run, we got pretty close agreement with Ott's result during the collapse, then after the star was stablized, we evolved further, the m=1 spiral mode grows up, and as the angular momentum is transported outside by the spiral structure, the core actually underwent a second but mild collapse, as a consquence of that, the m=1 mode was damped finnally. This scenario is exactly what New and Centrella suggested in their discussion on a centrifugally-hung core.

The following are the results for high resolution run.

Movies for the high resolution simulation
Resolution	# of processors	computer	plots	movies	comments
130194256	32Pentium 4	LSU Superhelix	\beta, angmom, modes, radial velocity at frame1300, radial velocity at frame 2000, angular velocity at frame 1300, angular velocity at frame 2000, velocity field at frame 2003, vrplots.ps, omega.ps, denmax comparison, \beta comparison, strain,	side view, top view,	The central purple shell denotes the nuclear density region.