University of Massachusetts Amherst |

**Title:** Well-posedness for the hard phase model with free boundary

**Abstract:** The hard phase model is a relativistic fluid model in which the fluid is assumed to be irrotational and the sound speed is assumed to be equal to the the speed of light. During gravitational collapse of the degenerate core of a massive star, the mass-energy density exceeds the nuclear saturation density and the sound speed approaches the speed of light. The hard phase is an idealized model for this physical situation.

In this talk, I will discuss recent work on the well-posedness of the hard phase model with vacuum free boundary in the Minkowski background, and extensions to the more general case of barotropic fluids with free

boundary.

This is joint work with Shuang Miao and Sijue Wu.