Neutron Star in 4U 1820-30 spins at 716 rotations per second

In their recent discovery, astronomers have observed a neutron star spinning at an astonishing speed of 716 rotations per second, making it one of the fastest spinning stars ever known. This neutron star, found in the binary system 4U 1820-30 within the globular star cluster NGC 6624, is located about 26,000 light-years from Earth in the constellation Sagittarius. Observed by NASA’s Neutron Star Interior Composition Explorer (NICER) aboard the International Space Station (ISS), the star’s surface also emits explosive thermonuclear blasts similar to atomic blasts.

Discovery and observations

Using data collected between 2017 and 2021, scientists from DTU Space have detected fifteen thermonuclear bursts on the star’s surface, one of which bore a clear signature indicates burst oscillations at 716 Hz. This confirmed the star’s rotation rate, which matched that of another rapidly spinning neutron star, PSR J1748–2446. “During these outbursts, the neutron star becomes up to 100,000 times brighter than the Sun, releasing enormous energy,” says Jerome Chenevez of DTU Space.

Extreme properties of neutron stars

Neutron stars, remnants of massive stars that have exhausted their nuclear fuel, are known for their extreme densities and fast rotations. When a star collapses in a supernova, its core condenses to a diameter of about 20 kilometers, but retains a mass up to twice that of our Sun. This rapid collapse causes it to spin at incredible speeds, a phenomenon explained by conservation of angular momentum. Furthermore, neutron stars in binary systems such as 4U 1820-30 often suck in matter from companion stars, further accelerating their rotation.

A new insight into binary star systems

The 4U 1820-30 system includes a white dwarf orbiting the neutron star at a rate of every 11 minutes, the shortest known orbital period for a binary star system. This fast orbit contributes to frequent matter transfers, creating conditions for explosive thermonuclear reactions on the neutron star’s surface.

These discoveries provide a unique view of the life cycle of neutron stars and the complex dynamics within binary systems.