This illustration shows how material is being dragged from the blue 'host star' towards a neutron star by the latters’ huge field of gravity and resulting in a nuclear reaction on the surface of the neutron star. (Illustration: NASA)

Scientists compile huge catalogue of wild explosions in space

Friday 14 Aug 20

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Jérôme Chenevez
Associate Professor
DTU Space
+45 45 25 97 03

An international cooperation

The scientific article and the new web data base is a the result of an international cooperation involving DTU Space at the Technical University of Denmark, Monash University in Australia, the Netherlands Institute for Space Research and with contributions from University of Amsterdam in The Netherlands, the Leibniz-Institut für Astrophysik in Germany, the University of Maryland in USA and ESA-agencies ESAC and ESTEC.

 

 

DTU has contributed to an international study that has examined decades of X-ray data and created the world’s largest collection of thermonuclear explosions on neutron stars in the Milky Way. More than 200.000 observations have been analysed. The study has been published in Astrophysical Journal Supplements.

By using data from satellite-based X-ray telescopes and collected over decades an international team of scientists has been able to assemble and analyse the largest collection yet of thermonuclear explosions on neutron stars in our Galaxy. 

These explosions take place when two stars – a sun like star and a neutron star where only the massive core is left - orbit around each other whereby material is being dragged from the former by the huge gravitation field of the latter.

The hydrogen and helium, thus accumulated on the surface of the dense and rapidly-spinning neutron star, burn through thermonuclear reactions. At some point the process leads to thermonuclear explosions that are detectable throughout the Galaxy as X-ray bursts lasting 10–100 seconds.

The collaborative work was led by researchers from Monash University in Australia leading a team of scientists from DTU Space, The National Space Institute, at the Technical University of Denmark as well as The European Space Agency (ESA) science institutions in the Netherlands, Spain, Germany and USA. 

“While some aspects of the burst physics are well understood, others are not,” says associate professor at DTU Space, Jérôme Chenevez who is part of the international team that have contributed to the study.

“Large samples such as this provide exciting new opportunities for all researchers to test new predictions and to use the bursts to learn more about neutron stars.”

"Large samples such as this provide exciting new opportunities for all researchers"
Jérôme Chenevez, associate professor at DTU Space

The analysis has just been published in the reputable scientific journal Astrophysical Journal Supplements.

Data available to other researchers via a web portal

And the huge new set of data is now collected in a data base and available to other researchers via a dedicated web portal. The data can be used by other scientists to study and compare these extreme events in our Milky Way to find more about how e.g. the natural elements of our Solar System came into being.

“These events are the most frequent thermonuclear explosions in the universe, and occur every few hours for the most prolific sources,” explains lead study author Duncan Galloway, associate professor at the Monash University School of Physics and Astronomy in Australia.

The explosions take place when a neutron star and a 'companion' star orbit each other. More than one hundred such sources are known in the Milky Way.

When a burst ignites it triggers a chain of hundreds of separate nuclear reactions, exhausting the available fuel and producing nuclear ‘ashes’ that will settle into the neutron star crust.

“Researchers can reproduce some of these reactions in labs here on Earth, but others are harder to reproduce, resulting in uncertainty for our model predictions,” said Duncan Galloway.

Study based on more than 200,000 separate observations

More than 7,000 events from 85 burst sources have been identified after analysing more than 200,000 separate observations.

“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,” said study co-lead Jean Zand from the Space Research Organisation of the Netherlands.

Researchers can use computer models together with the observations in the study sample to identify which of the many nuclear reactions are the most important to determine the burst properties, and help guide future nuclear physics experiments.

Measurements from bursts have been used to calculate the mass and radius of the host neutron stars, which may provide evidence of novel states of matter in their cores.

The new analysis results will provide a unique resource for future studies, including observations of these objects or others yet to be discovered, as well as computer modelling to better simulate the nuclear burning processes that take place during the events.

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