Shock Dynamics in Core-Collapse Supernovae

Research in the dynamics of core-collapse supernovae supporting the TeraScale Supernova Initiative

Spiral SASI Mode Generates Rotation Inside Supernovae

Using 2D hydrodynamic simulations on an equatorial grid, NCSU undergraduate student Samantha Shaw has demonstrated the existance of non-axisymmetric spiral modes of the SASI. Whereas the now familiar shoshing mode of the SASI is an acoustic wave propagating along a symmetry axis within the confines of the stalled supernova accretion shock, the spiral mode is the same acoustic wave propagating around a symmetry axis. The image at left illustrates the ability of this spiral SASI mode to generate two counter-rotating flows, explaining the remarkable ability of the SASI to spin up the accreting neutron star in 3D simulations (see below).

preprint.pdf (11MB)

More information is available on Samantha's Website

Neutron Star Spin-Up Discovered with 3D Simulations on Cray X-1

The image at left was generated from a 3D hydrodynamic simulation using 600 million zones. This simulation was computed on the Cray X-1 at the Oak Ridge National Labs. The slice through the center is shaded by pressure to show the extent of the young supernova shock. Outside this shock the stellar material is falling radially in towards the center of the collapsing star, as shown by the yellow streamlines in the outer regions. The flow is decelerated at the unstable shock (streamlines change from yellow to blue) and deflected from radial infall. These 3D simulations show that the flow develops into a strong, stable, rotational flow (streamlines wrapped around the proto-neutron star). The flow deposits enough angular momentum on the inner core to produce a young neutron star spinning with a period of only a few milliseconds.

Animation of gas entropy:
small - mpeg-4; large - quicktime

The SASI is identified with a growing acoustic mode confined within the accretion shock. The left image (and Quicktime animation) displays the gas pressure as the height and entropy as color. The pressure has been multiplied by r⁴ to remove the steep gradients of the equilibrium solution. The low entropy at small radius demarks the region of strong cooling just above the accreting star.

The right image (and Quicktime animation) illustrates the motion of the gas as the SASI evolves from the linear phase with nearly radial motion, to the non-linear phase with large tangential flows. The background color represents the gas entropy; Note that density perturbations move with the flow markers.

You can manipulate this visualization as a 3D object using the free 3D viewer from CEI, which you can downlood from http://www.ensight.com/products/enliten.html, and downloading the scenario file of this visualization: half_frame.els (20 Mb). Or you can download a quicktime animation of the unsteady flow: QT (10 Mb).

Here is an animation of the full evolution (75Mb).

Here is an enliten file of the flow field.

3D DATA: TSI makes available all of our 3D hydro data generated by VH-1. The datasets are accessible via the Logistical Network. To download the data you need to install the LoRS Tools and follow the instructions in the on-line tutorial.

Linear SASI paper: PDF, Figure 6 mpg, Figure 8 mpg