Physics of stellar mergers: implications for neutron star and black hole binaries and other stellar exotica

Advisor: Ondřej Pejcha (ITP MFF CUNI)

Funding: Fully funded



The recent detection of gravitational waves from merging binary black holes and binary neutron stars together with the associated electromagnetic emission opened a new window for studies of compact objects, stellar evolution, nucleosynthesis and related areas of astrophysics. To properly interpret the new discoveries coming from gravitational wave detectors and time-domain surveys, we need to understand the physical processes responsible for the formation of these sources. One of the crucial channels for formation of both binary black holes and binary neutron stars critically relies on “common envelope” evolution (CEE), when a binary star undergoes catastrophic interaction accompanied by the loss of mass, angular momentum and energy. In addition to gravitational wave sources, CEE plays a crucial role in the evolution of many compact object binaries composed of black holes, neutron stars and white dwarfs, cataclysmic variables, X-ray binaries, recycled pulsars, and other objects of interest. An alternative outcome of CEE is a merger of the binary components into a single object. In such cases, the remnants should appear as rapidly spinning and possibly magnetic stars, which potentially includes blue stragglers or mysterious objects such as the progenitors of SN1987A, SN2009ip, η Car, and long γ-ray bursts. In fact, about a third of massive stars and a comparable number of low-mass stars will experience CEE or similar interaction.

We seek 1-2 PhD students to work on topics related to the ERC Starting Grant "Catastrophic interactions of binary stars and the associated transients" (Cat-In-hAT). The work will focus on understanding the theory and observational implications of two merging stars, including neutron stars. Depending on the interests of the student, the work could focus on (magneto)hydrodynamical evolution of merger remnants, formation of dust and molecules, transients from stellar collisions, understanding the observational counterparts (blue stragglers, R CrB stars, FK Com stars, eta Car, progenitor of SN1987A, GW170817, etc.), and other projects. The work will utilize existing codes or codes under development in the group: multidimensional low-Mach number magnetohydrodynamics, moving mesh radiation hydrodynamics, 1D stellar evolution, or N-body calculations. In addition, the group is a member of All-Sky Automated Survey for Supernovae, and the thesis can include significant observational or data analysis component.