Asymmetric mass ratios for bright double neutron-star mergers
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 f...
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Veröffentlicht in: | Nature (London) 2020-07, Vol.583 (7815), p.211-214 |
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Zusammenfassung: | 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.
Pulsar timing measurements show a mass ratio of about 0.8 for the double neutron-star system PSR J1913+1102, and population synthesis models indicate that such asymmetric systems represent 2–30% of merging binaries. |
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ISSN: | 0028-0836 1476-4687 |
DOI: | 10.1038/s41586-020-2439-x |