International study reveals the nature of binary star systems

7th March 2023
Artist's impression of the blazing eruption of the neutron star Swift J1858 compared to the black hole GRS 1915+105.

An international scientific team, led by Dr Federico Vincentelli of the Instituto de Astrofísica de Canarias and featuring input from St Hilda’s Dr Jakob van den Eijnden (Lee Hysan Junior Research Fellow in Physical Sciences), has found a neutron star that captures matter from a companion star with a violent and unstable process. This mechanism, previously observed only in black holes, shows that the so-called ‘accretion instability’ is actually a fundamental physical process. The study has been published in the journal Nature.

Neutron stars (tiny remnants of stars with an incredibly high density) have incredibly strong gravitational pulls and often live in a binary system (where another normal star orbits arounds them). In this configuration, the gravitational pull from a neutron star can capture material from its neighbouring star. This process, known as accretion, usually occurs in violent eruptions during which the binary system becomes up to a thousand times brighter. The stolen gas falls towards the neutron star, after which two things can happen: some of the gas rains down onto the neutron star’s surface, while the rest is ejected back into space in so-called ‘jets’.

The study compared the data from a binary system containing a neutron star (Swift J1858.6-0814) with a system containing a black hole (GRS 1915+105) and found that the same instable process occurred in both in the process of gas capture and jet launching. This startling discovery shows how the nature of the ‘cannibal’ – black hole or neutron star – is irrelevant for the phenomenon.

Dr Jakob van den Eijnden’s research focuses on neutron stars and the connection between captured gas and jet-streams, and he observes this process with different telescopes on Earth and in space. In this particular study, Jakob performed observations with the Karl G. Jansky Very Large Array telescope in New Mexico, US, and specifically received the light emitted by the jet. Four other telescopes simultaneously observed the light emitted by the gas as it was captured.

The team now plan to extend this type of study to other luminous systems, to shed light on black holes and neutron stars when they incorporate matter at extreme speeds.

(Top) Artist's impression of the blazing eruption of the neutron star Swift J1858 compared to the black hole GRS 1915+105. Credit: Instituto de Astrofísica de Canarias.

(Right) Dr Jakob van den Eijnden