Home Science and Nature Massive Neutron Stars Could Contain Cores Made of Deconfined Quark Matter

Massive Neutron Stars Could Contain Cores Made of Deconfined Quark Matter

by News7

Neutron-star cores contain matter at the highest densities in our Universe. This highly compressed matter may undergo a phase transition where nuclear matter melts into deconfined quark matter, liberating its constituent quarks and gluons. But it is currently unknown whether the transition takes place inside at least some physical neutron stars. In a new study, physicists from the University of Helsinki, the University of Stavanger, Flatiron Institute and Columbia University quantified this likelihood by combining information from astrophysical observations and theoretical calculations.

An artist’s impression of a neutron star. Image credit: Sci.News.

Neutron stars are extreme astrophysical objects containing the densest matter found in the present-day Universe.

They have a radius on the order of 10 km (6 miles) and a mass of about 1.4 solar masses.

“A longstanding open problem concerns whether the immense central pressure of neutron stars can compress protons and neutrons into a phase called cold quark matter. In this exotic state, individual protons and neutrons no longer exist,” said University of Helsinki’s Professor Aleksi Vuorinen.

“Their constituent quarks and gluons are instead liberated from their typical color confinement and are allowed to move almost freely.”

In their new paper, Professor Vuorinen and colleagues provided a first-ever quantitative estimate for the likelihood of quark-matter cores inside massive neutron stars.

They showed that, based on current astrophysical observations, quark matter is almost inevitable in the most massive neutron stars: a quantitative estimate that they extracted placed the likelihood in the range of 80-90%.

The remaining small likelihood for all neutron stars to be composed of only nuclear matter requires the change from nuclear to quark matter to be a strong first-order phase transition, somewhat resembling that of liquid water turning to ice.

This kind of rapid change in the properties of neutron-star matter has the potential to destabilize the star in such a way that the formation of even a minuscule quark-matter core would result in the star collapsing into a black hole.

An artist’s impression of the different layers inside a massive neutron star, with the red circle representing a sizable quark-matter core. Image credit: Jyrki Hokkanen, CSC.

“A key ingredient in deriving the new results was a set of massive supercomputer calculations utilizing Bayesian inference, a branch of statistical deduction where one infers the likelihoods of different model parameters via direct comparison with observational data,” the authors explained.

“The Bayesian component enabled us to derive new bounds for the properties of neutron-star matter, demonstrating them to approach so-called conformal behavior near the cores of the most massive stable neutron stars.”

“It is fascinating to concretely see how each new neutron-star observation enables us to deduce the properties of neutron-star matter with increasing precision,” added University of Helsinki’s Dr. Joonas Nättilä.

“We had to use millions of CPU hours of supercomputer time to be able to compare our theoretical predictions to observations and to constrain the likelihood of quark-matter cores,” said Joonas Hirvonen, a PhD student at Flatiron Institute and Columbia University.

“We are extremely grateful to the Finnish supercomputer center CSC for providing us with all the resources we needed.”

The paper was published in the journal Nature Communications.

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E. Annala et al. 2023. Strongly interacting matter exhibits deconfined behavior in massive neutron stars. Nat Commun 14, 8451; doi: 10.1038/s41467-023-44051-y

Source : Breaking Science News

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