PSR J0740+6620

Lore & Background

PSR J0740+6620 held the record for the heaviest neutron star until July 2022, when the title was taken by PSR J0952–0607 with a reported mass of 2.35+0.17−0.17 M☉. Its own mass of 2.08+0.07−0.07 M☉ was determined by measuring the Shapiro delay of its white dwarf companion as the system passed edge-on to Earth. This measurement placed the star near the theoretical maximum mass for a neutron star. The star is estimated to measure 12.39+1.30−0.98 km (7.70+0.81−0.61 mi) across. Its rapid spin period of 2.8857 milliseconds and characteristic age of 3.75 billion years make it a stable cosmic clock. The discovery was made in 2019 using the Green Bank Telescope in West Virginia, U.S.

In Their Own Story

The radio dish hums in the cold night air of West Virginia. On the screen, the pulse arrives like a heartbeat from the void. I watch the waveform stabilize, knowing that at the source, gravity is so intense time itself bends. 3.75 billion years ago, this star was born. Now, its ghost spins in the dark, crushing atoms into a soup of neutrons. The data streams in, a mass of 2.08+0.07−0.07 M☉ that should not exist. I feel the weight of it in my chest, a silent pressure from a world where physics breaks. Its companion, a white dwarf, passes edge-on to Earth, and the Shapiro delay reveals the star's true heft. Until July 2022, it was the heaviest neutron star known, until PSR J0952–0607 took the title with 2.35+0.17−0.17 M☉.

Reader's Guide

Neutron stars form when massive cores collapse, stabilized by degeneracy pressure against crushing gravity. PSR J0740+6620's rapid spin of 2.8857 milliseconds and stable timing act as a cosmic clock for testing General Relativity. By tracking its white dwarf companion's orbit, researchers measure the Shapiro delay—where the companion's gravity stretches the pulse signal—to calculate the star's mass with unprecedented certainty. This mass of 2.08+0.07−0.07 M☉ places it near the theoretical maximum, indicating that neutron star matter is far stiffer than experts predicted. The star's estimated size of 12.39+1.30−0.98 km (7.70+0.81−0.61 mi) further constrains the Equation of State. Understanding such extremes informs our knowledge of the universe's fundamental limits.

Did You Know?

• PSR J0740+6620 was discovered in 2019 by astronomers using the Green Bank Telescope in West Virginia, U.S.
• It completes a spin period of 2.8857 milliseconds and has a characteristic age of 3.75 billion years.
• Its mass of 2.08+0.07−0.07 M☉ was calculated via the Shapiro delay of its white dwarf companion as it passed edge-on to Earth.
• It held the record for the heaviest neutron star until July 2022, when PSR J0952–0607 took the title with a reported mass of 2.35+0.17−0.17 M☉.
• The star is estimated to measure 12.39+1.30−0.98 km (7.70+0.81−0.61 mi) across.