Abstract
Neutron star (NS) is one of the most interesting astrophysical compact objects for hardronic physics. It is believed that the central density of NS can reach several times the normal nuclear matter density ( ρ 0). Hence, the inner part of NS is the ultimate testing place for the physics of dense matter. Recently, the mass of NS in a NS-white dwarf (WD) binary PSR J1614-2230 has been estimated to be 1.97 ± 0.04 M ๏ [1]. Since this estimate is based on the observed Shapiro delay, it can give the lower limit of the maximum NS mass and rules out many soft equations of state. On the other hand, all the well-measured NS masses in NS-NS binaries are smaller than 1.5 M ๏ . In this work, by introducing the supercritical accretion during the binary evolution, we propose a possibility of forming higher mass NS in NS-WD binaries. In this scenario, the lifetimes of NS and WD progenitors are significantly different, and NS in NS-WD binary can accrete > 0.5 M ๏ after NS formation during the giant phase of the progenitor of WD. On the other hand, for the binary system with NS and heavier (> 8 M ๏ ) giants, the first-born NS will accrete more from the companion and can collapse into black hole. The only way to avoid the supercritical accretion is that the initial masses of progenitors of NS binary should be very close so that they evolve almost at the same time and don’t have time to accrete after NS formation.
Highlights
Dense hadronic matter is the system in which the densities are higher than normal nuclear matter density ρ0
By introducing the supercritical accretion during the binary evolution, we propose a possibility of forming higher mass Neutron star (NS) in NS-white dwarf (WD) binaries
The only way to avoid the supercritical accretion is that the initial masses of progenitors of NS binary should be very close so that they evolve almost at the same time and don’t have time to accrete after NS formation
Summary
Dense hadronic matter is the system in which the densities are higher than normal nuclear matter density ρ0. Recent discovery of 1.97M NS, PSR J1614−2230, in a NS-WD binary has been reported [1] This observation is very important because this mass measurement is based on the Shapiro delay, for the first time in NS-WD binaries. If the mass of NS in PSR J1614−2230 is confirmed to be 1.97M , the maximum mass of NS has to be bigger than ∼ 2M This will rule out many EOS and can give constraints on many hadronic properties beyond normal nuclear matter density. The lack of supercritical accretion in NS-NS binaries can explain the current observation that all well measured NS masses in NS-NS binaries are < 1.5M This limit is independent of the maximum mass of NS, but the result of evolution of NS binaries. We suggest that the supercritical accretion to the first-born NS can explain both high mass NS in NS-WD binaries and the non-existence of high mass NS in NS-NS binaries
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