An international team of scientists, led by Professor Chris Done of our Physics Department, has made a surprising discovery about powerful winds blasting from around a neutron star.
A neutron star is the dense remains of a once-massive star.
Researchers used the X-Ray Imaging and Spectroscopy Mission (XRISM) to observe GX13+1, a bright X-ray source powered by a disc of hot matter spiralling into a neutron star.
These swirling ‘accretion discs’ often produce high-speed winds that shape their environment, but the exact processes behind them remain a mystery.
The team expected a clear look at these winds thanks to XRISM’s high-resolution X-ray measurements.
But they got an even bigger surprise: GX13+1 suddenly brightened to the Eddington limit - the point where energy from falling matter pushes most incoming material away.
This created an unusually thick wind, but it wasn’t moving as fast as expected.
Instead of reaching speeds close to 200 million km/h, like winds near supermassive black holes, GX13+1’s wind crawled along at about one million km/h.
Previous XRISM data showed winds near supermassive black holes, which are millions of times heavier than the Sun, were extremely fast and clumpy, not slow and smooth like GX13+1’s.
Both systems were at similar energy levels, so why the difference?
The answer may lie in temperature.
Accretion discs around giant black holes are cooler and emit ultraviolet light, which pushes matter more effectively than the X-rays from hotter, smaller discs around neutron stars.
This difference in radiation could explain why black hole winds are faster.
The findings could reshape our understanding of how energy and matter interact in extreme environments, influencing everything from how stars form to how galaxies grow.
Matteo Guainazzi, the European Space Agency’s (ESA) XRISM project scientist, described the discovery as ‘a game-changing moment’, adding: “We’re finally seeing details we’ve dreamed of for decades.”
Professor Done said: “It’s still surprising how slow and thick this wind is.
“It’s like looking at the Sun through a dense fog.”
XRISM is a mission led by the Japan Aerospace Exploration Agency (JAXA) in partnership with the European Space Agency (ESA) and NASA.
With XRISM’s powerful observations, astronomers are now better equipped to explore the extreme physics behind these cosmic winds and prepare for the next generation of space telescopes, like ESA’s upcoming NewAthena mission.
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