Astronomers Uncover One of the Fastest-Spinning Neutron Stars in the Milky Way

In a groundbreaking discovery, astronomers have identified a neutron star spinning at a mind-boggling rate of 716 rotations per second, placing it among the fastest-spinning objects ever observed.

Using data from NASA’s NICER X-ray telescope aboard the International Space Station, researchers have added a vital piece to the puzzle of understanding the extreme physical properties of neutron stars, which are some of the densest objects in the universe.

The Fast-Spinning Neutron Star 4U 1820-30

The neutron star in question, known as 4U 1820-30, resides in the constellation Sagittarius near the galactic center, roughly 26,000 light-years from Earth. It forms part of a unique X-ray binary system where a neutron star and a white dwarf orbit one another. This system is particularly extraordinary because the white dwarf orbits the neutron star every 11 minutes, making it the binary star system with the shortest known orbital period. “We were studying thermonuclear explosions from this system and then found remarkable oscillations, suggesting a neutron star spinning around its center axis at an astounding 716 times per second,” explained Dr. Gaurava K. Jaisawal from DTU Space, the Technical University of Denmark, and the study‘s lead author.

Neutron stars, often referred to as “dead stars,” are the remnants of massive stars that have undergone supernova explosions. Despite being only about 12 kilometers in diameter, these stars pack a mass 1.4 times that of the sun into a space the size of a city, making them incredibly dense. The rapid spin observed in 4U 1820-30 occurs as the neutron star accretes material from its white dwarf companion. This transfer of mass also transfers angular momentum, causing the neutron star to spin even faster. Such extreme conditions allow astronomers to probe the limits of neutron star physics, which remain one of the most enigmatic fields in astrophysics.

Observations Using NICER and X-Ray Bursts

Between 2017 and 2021, the research team used NICER (Neutron star Interior Composition Explorer) to monitor 4U 1820-30. NICER, which is equipped with star tracker technology from DTU Space, precisely aligns with distant neutron stars to collect detailed observations. During this period, astronomers recorded 15 thermonuclear X-ray bursts, each as violent and explosive as an atomic bomb. These bursts are triggered when the neutron star’s immense gravity pulls material from its white dwarf companion, leading to thermonuclear explosions on the neutron star’s surface.

“During these bursts, the neutron star becomes up to 100,000 times brighter than the sun, releasing an immense amount of energy,” said Associate Professor Jerome Chenevez from DTU Space, emphasizing the magnitude of these cosmic events. One of these bursts showed clear oscillations at a frequency of 716 Hz, matching the spin rate of the neutron star. The observed frequency strongly suggests that 4U 1820-30 rotates 716 times per second, tying the current record set by another neutron star, PSR J1748–2446ad.

Implications for Astrophysical Limits

This discovery raises compelling questions about the physical limitations of neutron stars. The 716 Hz spin rate appears to be near the maximum theoretical speed at which a neutron star can rotate without breaking apart. As neutron stars spin, centrifugal forces work against gravity, and reaching a spin limit could lead to the star’s structural instability. “If future observations confirm this, the 4U 1820-30 neutron star would be one of the fastest-spinning objects ever observed in the universe,” added Dr. Jaisawal, highlighting the significance of these findings.

Neutron stars offer a unique laboratory for understanding matter under extreme conditions. They are so dense that one teaspoon of neutron star material would weigh over a billion tons on Earth. Studying these objects helps scientists gain insight into the behavior of matter at nuclear densities, potentially revealing clues about the state of matter in the universe’s densest regions.

Future Research and the Path Ahead

The research team emphasizes that continued observations are essential for confirming the 716 Hz spin rate and understanding the factors influencing these rapid rotations. As astronomers gather more data, they hope to uncover whether other neutron stars approach or exceed this rotational boundary, providing a clearer picture of the forces that govern such extreme objects. Studying phenomena like 4U 1820-30 not only advances our understanding of stellar evolution but also sheds light on the life cycles of binary star systems and the origins of elements in the cosmos.

As technology improves and more advanced space telescopes come online, the mysteries of neutron stars will become clearer, yet the universe will undoubtedly continue to reveal new and surprising phenomena that challenge our understanding of physics.