Contributed Talk - Splinter Stellar

Friday, 25 September 2020, 16:59   (virtual room M)

White Dwarf Neutron Star Binaries and the Transients they Produce

Alexey Bobrick, Melvyn B. Davies, Ross Church
Lund University

White dwarf-neutron star binaries are an important class of compact binaries. When detached, they may be observed as binary radio pulsars and, in the future, as gravitational wave sources. As these binaries spiral into contact, depending on the mass of the white dwarf, they may result in long-lived stably-transferring ultra-compact X-ray binaries or experience a violent merger leading to a faint supernova-like event. At the beginning of mass transfer, all such binaries evolve through a short phase when mass transfer rates exceed the Eddington rate by many orders of magnitude, which leads to strong outflows from the binary. Mass loss which occurs during this stage has a significant impact on orbital stability of the systems. By modelling this phase through hydrodynamic simulations, we have recently shown, for the first time, that only the binaries with low-mass He white dwarfs can survive the onset of mass transfer. This conclusion agrees well with the observed formation rates and compositions of ultra-compact X-ray binaries and binary pulsars. We have recently obtained the first lightcurves and spectra for the merging systems, and show that they produce red faint short-lived, yet observable, transients.