PSR J0952-0607: The Fastest and Heaviest Known Galactic Neutron Star (2207.05124v1)

Abstract: We describe Keck-telescope spectrophotometry and imaging of the companion of the black widow" pulsar PSR~J0952$-$0607, the fastest known spinning neutron star (NS) in the disk of the Milky Way. The companion is very faint at minimum brightness, presenting observational challenges, but we have measured multicolor light curves and obtained radial velocities over the illuminatedday" half of the orbit. The model fits indicate system inclination $i=59.8\pm 1.9^\circ$ and a pulsar mass $M_{NS} = 2.35\pm 0.17 M_\odot$, the largest well-measured mass found to date. Modeling uncertainties are small, since the heating is not extreme; the companion lies well within its Roche lobe and a simple direct-heating model provides the best fit. If the NS started at a typical pulsar birth mass, nearly $1 M_\odot$ has been accreted; this may be connected with the especially low intrinsic dipole surface field, estimated at $6\times 10^7$G. Joined with reanalysis of other black widow and redback pulsars, we find that the minimum value for the maximum NS mass is $M_{\rm max} > 2.19 M_\odot$$(2.09 M_\odot)$ at $1\sigma$$(3\sigma)$ confidence. This is $\sim 0.15 M_\odot$ heavier than the lower limit on $M_{\rm max}$ implied by the white-dwarf--pulsar binaries measured via radio Shapiro-delay techniques.

• The paper determines PSR J0952-0607’s mass at 2.35±0.17 M☉, setting a new record and refining constraints on neutron star mass limits.
• The study employs direct-heating models and radial velocity measurements to accurately ascertain the system’s inclination and companion characteristics.
• The findings highlight substantial accretion history and its implications for dense-matter equations, advancing our understanding of neutron star evolution.

Overview of "PSR J0952-0607: The Fastest and Heaviest Known Galactic Neutron Star"

The paper on PSR J0952-0607 conducted by Romani et al. presents a comprehensive analysis of the neutron star (NS) within the binary system, which holds the dual distinction of being both the fastest-spinning and heaviest NS discovered in the Galactic field. The efforts hinge on data obtained through Keck-telescope spectrophotometry and imaging, aiming to unravel the characteristics of the "black widow" pulsar system. Such systems are typified by a low-mass companion being partially evaporated by the pulsar's radiation.

Key Findings

• Neutron Star Mass: The paper estimates the mass of PSR J0952-0607 at $M_{\rm NS} = 2.35 \pm 0.17\, M_\odot$. This value is notably the most massive NS identified to date, making it crucial for discussions surrounding the maximum mass (M_max) that NSs can attain.
• System Inclination and Companion Characteristics: The binary system's inclination is calculated at $i = 59.8 \pm 1.9^\circ$. Despite challenges due to the faintness of the companion at its minimum brightness, radial velocity measurements over its orbit's illuminated half were obtained. The companion does not fill its Roche lobe entirely, and a straightforward direct-heating model fits the observational data efficiently, indicating minimal systematic uncertainty in modeling.
• Implications for Neutron Star Evolution: The authors discuss the accretion history of the neutron star, which, if commencing from a typical NS birth mass, implies the accretion of nearly $1\,M_\odot$. The low intrinsic dipole surface field of approximately $6 \times 10^7$ G correlates with this evolutionary trajectory.

Numerical and Theoretical Implications

The authors assert that this system, alongside other black widow and redback pulsars, suggests a lower bound for the maximum NS mass greater than that indicated by white-dwarf-pulsar binaries measured via radio Shapiro-delay techniques. Specifically, the paper posits a minimum value for $M_{\rm max} > 2.19\,M_\odot$ at 1σ confidence, emphasizing the vital role these measurements play in constraining the dense-matter equation of state.

Speculations for Future Research

The detailed observations of PSR J0952-0607 provide a fertile ground for future studies into the angular momentum dynamics and evolutionary aspects of neutron stars in binary systems. With advancements in observational technologies, particularly with larger telescope arrays, it is plausible to anticipate even more precise mass measurements. Such developments would refine our understanding of both NS masses and the broader astrophysical processes driving neutron star binary evolution.

Overall, the inferences drawn from PSR J0952-0607 are pivotal for theoretical models of NS mass distribution, underlining the complexity and diversity of compact object binaries and the essential nature of observational precision in shedding light on their enigmatic properties.