Short gamma-ray bursts (sGRBs) are generally thought to result from the merger of two neutron stars or the merger of a neutron star with a black hole. It is becoming standard practise to model these mergers with hydrodynamical simulations that employ equations of state that are derived, for example, for determining the behaviour of matter in core-collapse supernovae (CCSNe), and which therefore make use of the assumption that the matter is hot and in nuclear statistical equilibrium (NSE). In this Letter we draw attention to the fact that the hydrodynamical timescale (roughly the gravitational timescale of the neutron star) may be several orders of magnitude shorter than the timescale on which such equilibrium can be re-established in the tidal debris ejected during a sGRB, and that on the initial decompression timescales the unshocked tidal ejecta may remain sufficiently cool that the employed equations of state are not appropriate for modelling the dynamics of this part of the flow. On timescales short compared with the timescale on which NSE can be (re)established, the equation of state can remain relatively stiff and thus the stream of tidal debris can remain narrow and vulnerable to gravitational instability, as has recently been suggested. These findings suggest that estimates of the type and abundances of heavy elements formed in short gamma-ray bursts need to be revisited. We suggest that the most direct method of testing the physical and dynamical properties of tidal ejecta in sGRBs will come from modelling of their light curves, which provides the cleanest source of information on the system dynamics.
Quantifying the impact of relativistic precession on tidal disruption event light curves
Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理研究所）；Institute of Theoretical Physics, Faculty of Mathematics and Physics, Charles University（查理大学数学与物理学院理论物理研究所）；Department of Physics and Columbia Astrophysics Laboratory, Columbia University（哥伦比亚大学物理学系与哥伦比亚天体物理实验室）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理中心）；Department of Physics and Astronomy, Purdue University（普渡大学物理与天文系）；Hamburger Sternwarte, Universität Hamburg（汉堡大学汉堡天文台）；The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University（斯德哥尔摩大学阿尔巴诺瓦天体物理奥斯卡·克莱因中心）
Tidal disruption events with SPH-EXA: resolving the return of the stream
University of Zurich（苏黎世大学）；Università degli Studi di Milano（米兰大学）；Syracuse University（雪城大学）；University of Leeds（利兹大学）；Swiss National Supercomputing Centre（瑞士国家超级计算中心）
The impact of recombination during tidal disruption events
School of Physics and Astronomy & Institute for Gravitational Wave Astronomy, University of Birmingham（伯明翰大学物理与天文学学院及引力波天文研究所）；Niels Bohr International Academy, Niels Bohr Institute（尼尔斯·玻尔国际学院，尼尔斯·玻尔研究所）
