Researchers from five different institutes, including SRON, have assembled and analysed the largest collection yet of thermonuclear explosions on neutron stars in our Galaxy. They used decades of data from NASA’s, ESA’s and Italian-Dutch X-ray telescopes to build their database.
Thermonuclear explosions on neutron stars are detectable as X-ray bursts and last between 10 to 100 seconds. They arise from runaway fusion reactions of accreted hydrogen and helium, coming from a companion star that orbits the neutron star once every few hours. More than one hundred thermonuclear explosions are known in our Galaxy. When a burst ignites, it triggers a chain of hundreds of separate nuclear reactions, exhausting the available fuel.
200,000 separate observations
‘We identified more than 7,000 events from 85 burst sources, after analysing over 200,000 separate observations,’ says study co-lead Jean in ‘t Zand from SRON Netherlands Institute for Space Research. ‘For a small team with no dedicated funding this took more than a decade to complete and we are glad we could carry this through and provide the community easy access to these exciting data.’
scientific goldmine
The database forms a scientific goldmine in two ways. First of all, the thermonuclear explosions create rare isotopes that we could never produce on Earth because of the extreme temperatures required—close to one billion degrees Celsius. Secondly, the explosions serve as bright markers in a neutron star’s surface, enabling astronomers to measure the stellar radius. Together with the mass this gives a neutron star’s density. With that information a neutron star is the best available laboratory for studying the strong nuclear force—one of the four fundamental forces.
Publication
Duncan K. Galloway, Jean in ‘t Zand, Jérôme Chenevez, Hauke Wörpel, Laurens Keek, Laura Ootes, Anna L. Watts, Luis Gisler, Celia Sanchez-Fernandez, and Erik Kuulkers, ‘The Multi-INstrument Burst ARchive (MINBAR)‘, The Astrophysical Journal