Merging Neutron Stars: What We Know So Far

[PAllen]

From my reading and discussions, it seems that the preferred model is that the SGRB, which occurred approximately 1.7 seconds after the time of merger inferred from the GW signal, is when the BH formed. Was this discussed in the verbal presentation? When you say "very quickly", do you mean on the time scale of seconds?

The 1.7 second delay was explained as primarily due to the last stage of inspiral producing GW of too high frequency to be detected. The occurrence of an SGRB per se says nothing about the nature of the remnant. On the other hand, a remnant NS is expected to be accompanied by a very strong neutrino flux (no, I don’t know why this is so, other papers are referred to; neutrino flux in NS formation from collapse is obvious, but why a merger resulting in NS would have one, I do not know). Then, prior work establishes (again, papers given) that a strong neutrino flux would suppress lanthanide production by the r process. The amount and timing of observed lanthanide production suggests that any NS remnant lasted less than 100 milliseconds before collapsing to a BH.

 

[PAllen]

Oh, another finding from the talk (and the paper I linked): the neutron star radii were likely 12 km at most. In the talk, this was said to rule out a number of NS equations of state.

 

[Jonathan Scott]

There's now a suggestion that the remnant was initially a neutron star, at least for several seconds, which would make it the largest one known:

Observational evidence for extended emission to GW170817: https://academic.oup.com/mnrasl/article/482/1/L46/5090425