Constraining the Maximum Mass of Neutron Stars from Multi-messenger Observations of GW170817
Abstract
We combine electromagnetic (EM) and gravitational-wave (GW) information on the binary neutron star (NS) merger GW170817 in order to constrain the radii {R}{ns} and maximum mass {M}\max of NSs. GW170817 was followed by a range of EM counterparts, including a weak gamma-ray burst (GRB), kilonova (KN) emission from the radioactive decay of the merger ejecta, and X-ray/radio emission consistent with being the synchrotron afterglow of a more powerful off-axis jet. The type of compact remnant produced in the immediate merger aftermath, and its predicted EM signal, depend sensitively on the high-density NS equation of state (EOS). For a soft EOS that supports a low {M}\max , the merger undergoes a prompt collapse accompanied by a small quantity of shock-heated or disk-wind ejecta, inconsistent with the large quantity ≳ {10}-2 {M}⊙ of lanthanide-free ejecta inferred from the KN. On the other hand, if {M}\max is sufficiently large, then the merger product is a rapidly rotating supramassive NS (SMNS), which must spin down before collapsing into a black hole. A fraction of the enormous rotational energy necessarily released by the SMNS during this process is transferred to the ejecta, either into the GRB jet (energy {E}{GRB}) or the KN ejecta (energy {E}{ej}), also inconsistent with observations. By combining the total binary mass of GW170817 inferred from the GW signal with conservative upper limits on {E}{GRB} and {E}{ej} from EM observations, we constrain the likelihood probability of a wide range of previously allowed EOSs. These two constraints delineate an allowed region of the {M}\max {--}{R}{ns} parameter space, which, once marginalized over NS radius, places an upper limit of {M}\max ≲ 2.17 {M}⊙ (90%), which is tighter or arguably less model-dependent than other current constraints.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2017
- DOI:
- arXiv:
- arXiv:1710.05938
- Bibcode:
- 2017ApJ...850L..19M
- Keywords:
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- equation of state;
- gravitational waves;
- stars: neutron;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- ApJL, accepted version