# Relativistic Shapiro delay measurements of an extremely massive millisecond pulsar

## TL;DR

This paper reports a precise measurement of the mass of the neutron star J0740+6620 using relativistic Shapiro delay, providing critical constraints on the equation of state of dense matter inside neutron stars.

## Contribution

The study combines long-term pulsar timing data with recent observations to measure the mass of an extremely massive neutron star, likely the most massive observed to date.

## Key findings

- Mass of MSP J0740+6620 is 2.14 solar masses with uncertainties.
- The measurement constrains the neutron star equation of state.
- It is likely the most massive neutron star observed.

## Abstract

Despite its importance to our understanding of physics at supranuclear densities, the equation of state (EoS) of matter deep within neutron stars remains poorly understood. Millisecond pulsars (MSPs) are among the most useful astrophysical objects in the Universe for testing fundamental physics, and place some of the most stringent constraints on this high-density EoS. Pulsar timing - the process of accounting for every rotation of a pulsar over long time periods - can precisely measure a wide variety of physical phenomena, including those that allow the measurement of the masses of the components of a pulsar binary system (Lorimer & Kramer 2005). One of these, called relativistic Shapiro delay (Shapiro 1964), can yield precise masses for both an MSP and its companion; however, it is only easily observed in a small subset of high-precision, highly inclined (nearly edge-on) binary pulsar systems. By combining data from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 12.5-year data set with recent orbital-phase-specific observations using the Green Bank Telescope, we have measured the mass of the MSP J0740+6620 to be $\mathbf{2.14^{+0.10}_{-0.09}}$ solar masses (68.3% credibility interval; 95.4% credibility interval is $\mathbf{2.14^{+0.20}_{-0.18}}$ solar masses). It is highly likely to be the most massive neutron star yet observed, and serves as a strong constraint on the neutron star interior EoS.