Speaker
Description
Compact binary millisecond pulsars, or 'spiders', consist of rapidly-spinning neutron stars spun up by a sustained accretion phase. As such, they are predicted to harbour the most massive neutron stars. These super-massive compact objects are paramount to finding the maximum neutron star mass, which has profound ramifications across many fields, such as gravitational wave astronomy, nuclear physics, and stellar astrophysics.
Using the largest ground-based telescopes and phase-resolved spectroscopy, we study the optical counterparts of these cannibalistic systems in which the rapidly-spinning pulsar ablates its companion with intense relativistic winds. This often results in substantial irradiation of the companion's surface, which actively hampers efforts to obtain accurate mass measurements -- the radial velocities measured become heavily biased towards the inner face, leading to large systematic uncertainties.
To counteract this effect, we use 'the power of the dark side' - we look for radial velocity signals associated with different atomic elements, which have different temperature sensitivities and thus can appear more strongly on the companion's night side face. This in turn results in higher radial velocities being measured from the dark side of the companion than from its irradiated face.
In our research, we found strong evidence of this occurring in two spider systems (PSR J1048+2339 and PSR J2055+1545), and tentative evidence in another (PSR J1810+1744), which allowed us to place constraints on the masses of both components in these systems. We also searched for such effects in a third system, PSR J1908+2105, and were surprised to find no strong radial velocity signals from it whatsoever. Instead, we were able to place upper limits on this system, which revealed the previously misunderstood spider to be in a near face-on orbit with one of the most massive companions discovered to date.