(Nanowerk News) An international scientific team led by the Institute of Astrophysics of the Canary Islands has found a neutron star that captures matter from a companion star in a violent and unstable process. This process, previously observed only in very bright black holes, opens the door to new insights into the behaviour of stars.
Artistic representation of the flares in the Swift J1858 neutron star compared to the GRS 1915+105 black hole. (Image: Gabriel Pérez Díaz, IAC)
X-ray binaries are systems that consist of a compact object, a neutron star or a black hole, and a star of a similar size to the Sun. The compact object swallows matter from the companion star through a disk that emits large amounts of light, especially in X-rays. This process in which the compact object attracts matter, known as accretion, usually occurs in violent eruptions during which the system becomes up to a thousand times brighter.
The X-ray binary Swift J1858.6-0814 was discovered in 2018 during one of these spectacular eruptive episodes, baffling the astronomical community since the earliest observations. It showed incredible flares for a year, emitting at all wavelengths from radio waves to X-rays. The origin of these cosmic fireworks was unknown, but they were so bright that the scientific community believed that the compact object must be a black hole. However, the 2020 discovery of thermonuclear explosions identified the presence of a solid surface on the compact object, thus confirming that Swift J1858 contains a neutron star.
Thanks to an international multi-telescope observing campaign led by the Institute of Astrophysics of the Canary Islands (IAC) and involving researcher Yuri Cavecchi, from the Department of Physics, linked to the Barcelona East School of Engineering (EEBE), and the Astronomy and Astrophysics Group of the Universitat Politècnica de Catalunya – BarcelonaTech (UPC), the team has now discovered that Swift J1858 exhibits the same exotic accretionary instabilities as GRS 1915+105, a black hole that has served as a Rosetta Stone to decipher the complex behaviour of this neutron star.
This study demonstrates that such “instabilities” are a fundamental physical process and independent of the nature of the compact object that is feeding on matter. This work presents a new scenario that allows to explain what happens in the vicinity of these exotic objects—neutron stars and black holes—when they accrete matter at very high rates.
