In a recent article published in the journal Nature Communications, a group of researchers from the University of Helsinki proposed the existence of a cold quark substance in the dense matter of neutron stars.
Astrophysicists have long been intrigued by neutron stars, which are incredibly dense objects with masses up to two times that of the Sun and diameters of only 25 km. One of the key questions surrounding these celestial bodies is whether the immense pressure at their cores can cause protons and neutrons to compress into a new phase of matter.
According to Alexy Voinenen, a professor of theoretical physics of elementary particles at the University of Helsinki, in a cold quark substance, protons and neutrons no longer exist as separate particles. Instead, their components, quarks and glows, are released and can move freely.
This new research provides the first quantitative assessment of the likelihood of quark nuclei in massive neutron stars. Based on current astrophysical observations, there is an 80-90% probability of a quark substance being present in the most massive neutron stars.
However, there is a small possibility that neutron stars consist entirely of nuclear substance, with no quark nuclei. This would require a strong phase transition similar to the freezing of liquid water into ice. The sudden change in a star’s properties could lead to instability and collapse into a black hole if even a small core of quark substance is formed.
An international team of scientists from Finland, Norway, Germany, and the United States have also outlined a method to confirm or refute the existence of quark nuclei in the future. This relies on the detection of gravitational wave signals during the final stages of neutron star mergers, which would allow for the assessment of the strength of the phase transition between nuclear and quark matter.
The study involved extensive calculations on supercomputers using the Bayes-out conclusion method, a statistical approach that evaluates the probabilities of different model parameters based on direct comparison with observations. Dr. Jonas Nyatil, one of the leading authors of the article, describes the work as an interdisciplinary effort, requiring knowledge in astrophysics, particle physics, nuclear physics, and computer science.
Jonas Hirvonen, a graduate student involved in the research, highlights the importance of high-performance computing in comparing theoretical forecasts with observations and evaluating the likelihood of quark nuclei. The project required millions of hours of supercomputer work.