Asymmetric mass ratios for bright double neutron-star mergers

R. D. Ferdman, P. C. C. Freire, B. B. P. Perera, N. Pol, F. Camilo, Shami Chatterjee, J. M. Cordes, Fronefield Crawford, J. W. T. Hessels, V. M. Kaspi, M. A. McLaughlin, E. Parent, I. H. Stairs, Joeri van Leeuwen

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)


The discovery of a radioactively powered kilonova associated with the binary neutron-star merger GW170817 remains the only confirmed electromagnetic counterpart to a gravitational-wave event(1,2). Observations of the late-time electromagnetic emission, however, do not agree with the expectations from standard neutron-star merger models. Although the large measured ejecta mass(3,4 )could be explained by a progenitor system that is asymmetric in terms of the stellar component masses (that is, with a mass ratio q of 0.7 to 0.8)(5), the known Galactic population of merging double neutron-star systems (that is, those that will coalesce within billions of years or less) has until now consisted only of nearly equal-mass (q> 0.9) binaries(6). The pulsar PSR J1913+1102 is a double system in a five-hour, low-eccentricity (0.09) orbit, with an orbital separation of 1.8 solar radii(7), and the two neutron stars are predicted to coalesce in 470(-11)(+12) million years owing to gravitational-wave emission. Here we report that the masses of the pulsar and the companion neutron star, as measured by a dedicated pulsar timing campaign, are 1.62 +/- 0.03 and 1.27 +/- 0.03 solar masses, respectively. With a measured mass ratio of q= 0.78 +/- 0.03, this is the most asymmetric merging system reported so far. On the basis of this detection, our population synthesis analysis implies that such asymmetric binaries represent between 2 and 30 per cent (90 per cent confidence) of the total population of merging binaries. The coalescence of a member of this population offers a possible explanation for the anomalous properties of GW170817, including the observed kilonova emission from that event.

Original languageEnglish
Pages (from-to)211-214
Number of pages4
Issue number7815
Publication statusPublished - 8 Jul 2020



Cite this