On the Possibility of GW190425 Being a Black Hole-Neutron Star Binary Merger

Koutarou Kyutoku, Sho Fujibayashi, Kota Hayashi, Kyohei Kawaguchi, Kenta Kiuchi, Masaru Shibata, Masaomi Tanaka

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)


We argue that the kilonova/macronova associated with the gravitational-wave event GW190425 could have been bright enough to be detected if it was caused by the merger of a low-mass black hole (BH) and a neutron star (NS). Although tidal disruption occurs for such a low-mass BH is generally expected, the masses of the dynamical ejecta are limited to ≲10-3 M o, which is consistent with previous work in the literature. The remnant disk could be as massive as 0.05-0.1 M o, and the disk outflow of ∼0.01-0.03 M o is likely to be driven by viscous or magnetohydrodynamic effects. The disk outflow may not be neutron-rich enough to synthesize an abundance of lanthanide elements, even in the absence of strong neutrino emitter, if the ejection is driven on the viscous timescale of ⪆0.3 s. If this is the case, the opacity of the disk outflow is kept moderate, and a kilonova/macronova at the distance of GW190425 reaches a detectable brightness of 20-21 mag at 1 day after merger for most viewing angles. If some disk activity ejects the mass within ∼0.1 s, instead, lanthanide-rich outflows would be launched and the detection of emission becomes challenging. Future possible detections of kilonovae/macronovae from GW190425-like systems will disfavor the prompt collapse of binary NSs and a non-disruptive low-mass BH-NS binary associated with a small NS radius, whose mass ejection is negligible. The host-galaxy distance will constrain the viewing angle and deliver further information about the mass ejection.

Original languageEnglish
Article numberL4
JournalAstrophysical Journal Letters
Issue number1
Publication statusPublished - 2020 Feb 10

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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