Top Spin: Neutron star discovered to spin at an astonishing 716 times

Researchers have discovered that the neutron star in the binary system 4U 1820-30 spins at an astonishing 716 times per second, making it one of the fastest-spinning objects ever observed in the Universe. The discovery was made by a research team led by astrophysicist Gaurava K. Jaisawal from the Technical University of Denmark, and the results were published in The Astrophysical Journal. While studying thermonuclear bursts in this system, they discovered unusual fluctuations indicating the rapid rotation of the neutron star.

“While we were studying thermonuclear bursts in this system, we discovered extraordinary fluctuations indicating that the neutron star is spinning on its axis at an astonishing rate of 716 times per second,” said Jaisawal, senior scientist at DTU Space. According to the researcher, if the collected data is confirmed, the neutron star 4U 1820-30 will be one of the fastest spinning objects ever observed in the Universe, second only to another neutron star called PSR J1748-2446.

The phenomenon was discovered by NASA’s Neutron Star Interior Composition Survey (NICER) on the International Space Station, which recorded 15 explosions between 2017 and 2022. Researchers have detected 15 thermonuclear X-ray bursts in a 4U X-ray binary star system. 1820-30 during this period. By analyzing data from these explosions, they discovered an unusual oscillation at a frequency of 716 Hertz, suggesting that the neutron star in 4U 1820-30 may have been an X-ray pulsar. Additional observations will be required to confirm this conclusion. If confirmed, the results will provide a new tool for studying neutron stars and understanding how far they can travel before they self-destruct.

Astrophysicist Jerome Cheneves from the Technical University of Denmark said: “During these explosions, the neutron star becomes 100,000 times brighter than the Sun, releasing enormous amounts of energy. So we are dealing with very extreme events, and by studying them, we gain new information about the life cycles that exist in binary star systems and about the formation of elements in the Universe.” He adds: “So we’re dealing with very extreme events, and by studying them in detail, we’re gaining new insight into the fascinating life cycles of binary star systems and the formation of elements in the Universe.”

Neutron star 4U 1820-30 is located approximately 26,000 light-years from Earth in the constellation Sagittarius, within the globular cluster NGC 6624. It has 1.4 times the mass of the Sun and is only 12 kilometers (about 7.5 miles) across . These extremely compact objects have a mass between 1.1 and 2.3 solar masses, but are compressed into a sphere with a diameter of only 20 kilometers.

4U 1820-30 is a binary system comprising a neutron star and a white dwarf star roughly the same size as Earth, with a narrow orbit allowing the neutron star to complete its orbit in just 11.4 minutes. The proximity of the two stars is such that the neutron star is constantly pumping material out of its white dwarf companion, allowing it to devour its companion and starve it of material. This material accumulates on the surface of the neutron star, becoming denser and hotter until it reaches critical mass and explodes in a violent thermonuclear explosion, similar to an atomic bomb, releasing incredible amounts of energy.

Neutron stars are one of the final stages in the evolution of a massive star, formed when stars with at least eight times the mass of the Sun run out of fuel for nuclear fusion. A star with a mass between 8 and 30 solar masses, after exhausting the fuel in its core, undergoes a collapse that can result in a powerful supernova explosion, ejecting outer material while the core collapses under the influence of gravity, causing a neutron star.

Neutron stars are extreme in many ways and are the densest objects ever observed in space, as they are the remnants of massive stars after a supernova explosion. The matter inside neutron stars can behave in unusual ways, and it is difficult to find words to describe their density: the matter they are made of can become truly strange, as can their behavior. A pulsar is a neutron star that spins at breakneck speeds, emitting beams of radio waves from its poles that spread out into space, creating the appearance of a cosmic beacon that constantly pulsates. Neutron stars are known to spin quickly, with some spinning hundreds of times per second.

NASA’s NICER (Neutron Star Interior Composition Explorer) is equipped with star tracking technology that enables precise targeting of distant neutron stars. Data collected by NICER played a crucial role in determining the rapid rotation of the neutron star in 4U 1820-30. Eventually, the accumulation of material causes thermonuclear explosions, which can create heavy elements such as gold and platinum. By studying these extreme events in detail, researchers are gaining new insights into the fascinating life cycles of binary star systems and the formation of elements in the Universe.

The 4U binary star system 1820-30 has the shortest orbital period ever observed and has been known to exist since at least the 1980s. The neutron star and its white dwarf companion have a volatile relationship, with the white dwarf orbiting the neutron star every 11 minutes, making it the system with the shortest known orbital period at 685 seconds. This discovery opens up new possibilities for studying the evolution of neutron stars. If confirmed, it would provide a new tool for understanding how far neutron stars can travel before self-destructing.

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Sources: Science Alert, Scienze Notizie, Spektrum der Wissenschaft, Mashable.

This article was written in collaboration with generative artificial intelligence company Alchemiq.