Super-Eddington accretion as a possible scenario to form GW190425

Abstract

On 2019 April 25, the LIGO/Virgo Scientific Collaboration detected a compact binary coalescence, GW190425. Under the assumption of the binary neutron star (BNS), the total mass of $3.4^{+0.3}_{-0.1}\, M_\odot$ lies five standard deviations away from the known Galactic population mean. In the standard common envelope scenario, the immediate progenitor of GW190425 is a close binary system composed of an NS and a He-rich star. With the detailed binary evolutionary modeling, we find that in order to reproduce GW190425-like events, super-Eddington accretion (e.g., $1,000\, \dot{M}_{\rm Edd}$) from a He-rich star onto the first-born NS with a typical mass of 1.33 M⊙ via stable Case BB mass transfer (MT) is necessarily required. Furthermore, the immediate progenitors should potentially have an initial mass of MZamsHe in a range of 3.0 − 3.5 M⊙ and an initial orbital period of Pinit from 0.08 days to 0.12 days, respectively. The corresponding mass accreted onto NSs via stable Case BB MT phase varies from 0.70 M⊙ to 0.77 M⊙. After the formation of the second-born NS, the BNSs are expected to be merged due to gravitational wave emission from ∼ 11 Myr to ∼ 190 Myr.

A Channel to Form Fast-spinning Black Hole–Neutron Star Binary Mergers as Multimessenger Sources. II. Accretion-induced Spin-up

“…where M c = 2.5 M e and M scale = 1.57 M e (see also Steiner et al 2012); Model II: uniform BH mass distribution in a range of 2.5-5.0 M e + power-law function from 5.0-15 M e with a slope index of −4.8, and here we adopt 5.0 M e as a connecting point between the two functions (also see power-law et al 2010, but with different values of mean and standard deviation in order to match the observation of GWTC-3). In addition, we simply assume a power-law distribution for the initial He-rich star mass (i.e., µ -dN dM M ZamsHe ZamsHe 3.3 , similar to the initial mass function as in Kroupa (2001), but with an index of −3.3) within a range of [2.5,10] M e in which NS is formed, and adopt a uniform distribution for the initial periods of BH-He-rich binaries in logarithmic space, i.e., [0.04, 40] days (similar to the range in Zhang et al 2023, see their Section 4.3).…”