Scientific context

Since the first LIGO detection in 2015, gravitational-wave (GW) astronomy has significantly advanced our understanding of compact binary star systems, primarily black holes (BHs). With the LIGO, Virgo, and KAGRA (LVK) detector network, as well as future observatories such as the Einstein Telescope, additional GW sources are expected to be observed in the future, including supernova core collapse (SNCC), which is the focus of this project.

The physics of the gravitational collapse of the massive star inner core is an active area of research today. It involves modelling a complex sequence of intertwined physical processes through large-scale, general-relativistic, multidimensional magnetohydrodynamics simulations, which also incorporate detailed microphysics, including nuclear and neutrino physics. 

A set of examples of GW signals associated with SNCC can be obtained from those simulations. While these simulated waveforms are not expected to match observations exactly, they exhibit features—such as spectral modes with varying frequencies—that can be qualitatively linked to the system’s structural and dynamical properties. The mode polarization is one of the key predictions that can be extracted from these simulations.

The objective of this Master’s research project is to determine to what extent the polarization information can be extracted from LVK detector data and how it relates to the underlying physics.

This project will first explore how multi-detector observations can be leveraged to reconstruct the original GW signal, specifically its two polarization modes, conventionally denoted h₊ and hₓ, along with their time-dependent relationship. Both model-agnostic and model-dependent approaches will be considered, building on recent advances made in the study of BH binaries using time-frequency representations of Stokes parameters to describe GW polarization.

Goals of the internship

1. Build a dataset of simulated GWs from SNCCs using the results of state-of-the-art physical models.

2. Characterize the polarisation in GWs from SNCC (multimodal? Time-evolving? etc.). 

3. Propose a proof of concept of end-to-end restoration of the SNCC polarizations with a realistic detector network.

Requirements

• Master 2 level in astrophysics and general relativity

• Basic notions of Python and data analysis

Supervisors

The intern will work at the APC laboratory of Université Paris Cité. They will be supervised by 

• Eric Chassande-Mottin and Pierre Palud (APC laboratory of the Université Paris Cité), for the data analysis part

• Thierry Foglizzo and Jérôme Guilet (AIM/CEA), for the supernova expertise and the physical models.