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Neutron stars as a laboratory for dense matter

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Sneak peek inside neutron stars

EU-funded physicists have gained glimpses of the interior of neutron stars, combining observations with theoretical calculations to pin down the nature of matter in these ultra-dense stellar corpses.

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Neutron stars are the remnants of supernovae explosions whose matter is so dense that atoms melt into their constituents, mainly neutrons. Their density is so high that a teaspoon of the ultra-dense matter would weigh about 6 billion tonnes on Earth. Some neutron stars also possess strong magnetic fields that are a million billion times stronger than the Earth’s magnetic field. Not surprisingly, neutron stars offer a unique laboratory for EU-funded scientists to test matter in extreme conditions that cannot be reproduced in any Earth laboratory. The ultimate aim of the NSLABDM (Neutron stars as a laboratory for dense matter) project was to constrain the properties of supranuclear matter in their interior with measurements of neutron star masses, radii and cooling rates. The results represent a significant advancement in our current understanding of strongly interacting matter. Properties of the hot and dense environment in neutron stars’ cores were studied within the framework of effective field theories. NSLABDM scientists were able to use data on strange mesons in heavy ion collision experiments to produce an equation for the state of nuclear matter for densities up to three times the nuclear matter saturation threshold. From this relationship between density, temperature and pressure, they could estimate a limit for the highest allowed neutron star mass. Furthermore, at extremely high pressure levels inside neutron stars, neutrons paired up. These pairs relax into the lowest possible energy state that quantum physics allows and convert to a superfluid. NSLABDM scientists analysed different dissipative processes to derive transport coefficients that are key to understanding the microscopic physics of dense superfluid matter. All the results obtained have been described in a wide range of NSLABDM publications. Research outcomes provide valuable insights into both how fundamental particles interact and the material forming neutron stars.


Neutron stars, ultra-dense, supernovae, magnetic field, NSLABDM, heavy ion collision

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