  The inspiral and merger of a binary neutron star (NSNS) can lead to the
formation of a hypermassive neutron star (HMNS). As the HMNS loses thermal
pressure due to neutrino cooling and/or centrifugal support due to
gravitational wave (GW) emission, and/or magnetic breaking of differential
rotation it will collapse to a black hole. To assess the importance of
shock-induced thermal pressure and cooling, we adopt an idealized equation of
state and perform NSNS simulations in full GR through late inspiral, merger,
and HMNS formation, accounting for cooling. We show that thermal pressure
contributes significantly to the support of the HMNS against collapse and that
thermal cooling accelerates its "delayed" collapse. Our simulations demonstrate
explicitly that cooling can induce the catastrophic collapse of a hot
hypermassive neutron star formed following the merger of binary neutron stars.
Thus, cooling physics is important to include in NSNS merger calculations to
accurately determine the lifetime of the HMNS remnant and to extract
information about the NS equation of state, cooling mechanisms, bar
instabilities and B-fields from the GWs emitted during the transient phase
prior to BH formation.
