The fastest-spinning star known turns 716 times a second

The fastest-spinning star known is PSR J1748-2446ad, a pulsar that rotates 716 times every second in the globular cluster Terzan 5, about 28,000 light-years away in Sagittarius. Announced in January 2006 by a team led from McGill University using the Green Bank Telescope, it broke a 642 Hz record that had stood for 23 years.

For scale, the fastest settings on common kitchen blenders run at about 250 to 500 Hz. Pulsars are spinning neutron stars, the collapsed cores left behind when massive stars explode, and they sweep beams of radio waves across space like lighthouses, so each turn reaches Earth as a precisely timed pulse.

How big can a star that fast be?

Its radius must be under about 16 kilometres, because the spin rate works as a measuring stick. If the star were too large, material at its equator would be flung into orbit. That limit assumes it weighs less than two Suns, which matched every neutron star weighed at the time; at that size, its equator would be moving at up to nearly a quarter of the speed of light.

“Our observations of such a rapidly rotating star set a hard upper limit on its size, and hence on how dense the star can be.” — Jason Hessels, McGill University

Why hasn’t anything beaten it?

Possibly because faster ones are hard to see. The discoverers expected to be overtaken. The pulsar is faint, and its companion star, which it orbits every 26 hours, hides it for about 40% of each orbit. That difficulty, they wrote, suggests that even faster-spinning neutron stars exist and are being missed.

Two decades on, the record still stands. One of the nearest rivals is PSR J0952-0607, discovered in 2017 and spinning 707 times a second. In 2022, UC Berkeley and Stanford astronomers found it is also the heaviest neutron star yet weighed, at 2.35 times the Sun’s mass, built up by shredding and consuming nearly all of its companion star.