What is the role of thermal pressure in hypermassive neutron star merger remants?

Submitted by cott on Wed, 06/19/2013 - 00:18

The merger of two neutron star creates a hypermassive, extremely rapidly and differentially spinning object (frequently called a hypermassive neutron star [HMNS]). While the premerger neutron stars can be treated as essentially being cold, the impact of the two NSs leads to very strong shocks that leave the HMNS with temperatures in the range of ~5-40 MeV (1 MeV corresponds to about 1.16 x 10^{10} K). For progenitor NSs in the typical NS mass range (1.3-1.4 solar masses), the HMNS will have more baryonic mass than can be supported by the nuclear equations of state and is believed to be supported by rapid differential rotation and, possibly, thermal pressure. Kaplan et al. have investigated the role of thermal pressure support in HMNS and found something surprising and counter-intuitive: thermal pressure contributions do not appear to enhance the maximum HMNS mass; they do increase the baryonic mass supported by sub-critical configurations (i.e. not peak density, not critically rotating), but do not appear to give a significant boost to the overall maximum. Read more in Kaplan et al. 2014, which has been submitted to the Astrophysical Journal. It's available on arXiv! We provide some code and the employed equation of state tables here on stellarcollapse.org/kaplanetal2014.