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Double neutron star (DNS) systems are one of the most important
classes of objects used to test and understand numerous astrophysical
and fundamental physics phenomena, including general relativity (GR)
in the strong-field regime.
These systems essentially consist of two-point masses, whose orbital
motion and evolution are well defined by GR.
Sengar et al. report the discovery with the Parkes 64m radio-telescope, Murriyang,
of the pulsar PSR J1325−6253: a DNS system in a 1.81 day orbit with
a surprisingly low eccentricity of just e = 0.064.
The figure above shows the mass–mass diagram for PSR J1325−6253
showing constraints on the pulsar mass and the companion mass. The
panels on the top and to the right show the probability distribution
functions for the pulsar and companion masses assuming an isotropic
inclination distribution (in light blue) and distribution using the
astrophysical priors (pink). The grey region in the main panel is
excluded due to the constraint on the binary mass function
corresponding to the maximum possible orbital inclination angle.
Other black dotted lines represent companion mass limits for various
orbital inclinations. The solid blue line represent the measured rate
of periastron advance and the dotted blue lines represent the +/-1𝜎
uncertainty range. The vertical and horizontal dashed black lines
correspond to the minimum and maximum pulsar and companion masses
among the known DNS systems for which both masses are well
measured. The well-measured masses for individual DNS systems are
shown in blue points.
The authors conclude that PSR J1325-6253 is a recycled pulsar and, if
its mass is similar to other known examples (>1.3 solar masses), then
the companion neutron star is probably less than ~1.25 solar masses
and the system is inclined at about 50--60 degrees. The low eccentricity
along with the wide orbit of the system strongly favours a formation
scenario involving an ultra-stripped supernova explosion.
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