PSR J0740+6620

Provenance-Backed Scientific Measurements

Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.

J2000 Equatorial Sky Chart & Culmination Altitude

The chart below plots PSR J0740+6620 — Record Massive Neutron Star at RA 07h 40m 45.80s, Dec +66° 20′ 33.6″ within Camelopardalis, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.

Astrophysical Context & Structure

Discovered in 2012 during the Green Bank Northern Celestial Cap Pulsar Survey, PSR J0740+6620 is a recycled millisecond pulsar spinning once every 2.8857 milliseconds (346.5 rotations per second) in northern Camelopardalis. It orbits an ultra-cool helium white dwarf companion every 4.767 days along an orbital plane inclined at 87.5 degrees to our line of sight. Because the radio pulses pass directly through the gravitational well of the white dwarf at superior conjunction, general-relativistic Shapiro time delays enabled astronomers to weigh the neutron star at 2.08 ± 0.07 solar masses—the heaviest precisely weighed neutron star on record.

How matter behaves at several times nuclear saturation density inside a neutron star core is one of the central open questions in fundamental physics. Many proposed 'soft' equations of state involving hyperons or deconfined quark matter predicted that neutron stars should collapse into black holes below 2.0 solar masses, or shrink steeply in radius as they approach maximum mass. In 2021, NASA's Neutron Star Interior Composition Explorer (NICER) aboard the International Space Station modeled gravitational light-bending from hot X-ray polar caps on PSR J0740+6620, measuring its radius at ~12.4 kilometers—nearly identical to that of a 1.4-solar-mass neutron star and confirming a stiff nuclear equation of state.

Thanks to its microsecond rotational stability, PSR J0740+6620 also serves as one of the flagship clock pulsars monitored by NANOGrav and the International Pulsar Timing Array to detect nanohertz gravitational waves from supermassive black hole binaries.

Practical Visual Observing Guide

• The ultra-cool white dwarf companion is exceptionally faint (R > 26), accessible only to the Hubble, Keck, and Gemini observatories.
• Monitored at radio frequencies by the Green Bank Telescope and CHIME at a dispersion measure of 14.96 pc/cm³.
• Exhibits a 25-microsecond relativistic Shapiro delay spike once every 4.77 days during superior conjunction.

Catalog Cross-Identifications & Aliases

Common Aliases: MSP J0740+6620 · 4FGL J0740.7+6620

Related Objects, Comparisons & Guides

Scientific Sources & Dataset Provenance

• SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg