Deep within neutron stars, the densest objects in the modern universe, there is a possibility that a substance called cold quark matter exists. This assumption was made by a group of researchers from the University of Helsinki in a paper published in the journal Nature Communications. Neutron stars contain up to two solar masses in a sphere just 25 km in diameter and are being studied as unique astrophysical objects. Of particular interest is the question of whether the huge central pressure of a neutron star could cause protons and neutrons to be compressed into a new phase of matter.

Alexi Vuorinen, professor of particle theory at the University of Helsinki, explains: “In cold quark matter, protons and neutrons no longer exist as separate particles.” Their constituent quarks and gluons are freed and free to move. Researchers have made the first quantitative estimate of the possibility that quark nuclei exist in massive neutron stars. Current astrophysical observations indicate an 80-90% chance that quark matter exists in the most massive neutron stars. However, it is unlikely that all neutron stars are composed only of nuclear material.

An international team of scientists from Finland, Norway, Germany and the United States has also shown how in the future it may be possible to completely confirm or deny the existence of quark nuclei. The key point here is the possibility of limiting the strength of the phase transition between nuclear and quark matter, which is possible by recording gravitational wave signals from the final stages of the merger of two neutron stars.

A key part of the research was large-scale computation on a supercomputer using Bayesian inference methods. Bayesian inference is a field of statistical inference that estimates the probabilities of various model parameters based on direct comparisons with observed data. Dr. Jonas Nätilä, one of the paper’s lead authors, described the research as an interdisciplinary effort that required expertise from astrophysics, particle physics, nuclear physics, and computer science. . He emphasizes that with each new observation of a neutron star, the properties of its material can be determined more precisely.

source: https://www.nature.com/articles/s41467-023-44051-y