Débora Mroczek 

University of Illinois Urbana-Champaign, November 14, 12:30 pm

New phases of matter in neutron stars: the path to discover

Recent advances have enabled precise joint mass–radius measurements of isolated neutron stars through Shapiro-delay observations and X-ray timing with NASA’s Neutron Star Interior Composition Explorer (NICER) aboard the International Space Station. The first NICER results suggest that 1.4 and 2.0 solar-mass neutron stars have remarkably similar radii, hinting that the equation of state (EoS) — the relation between pressure and density that determines how massive and compact these stars can be — becomes stiffer at high densities. This trend could signal the emergence of new phases of matter in the cores of massive neutron stars. Yet, drawing statistically robust conclusions about their interior composition remains difficult due to large theoretical and observational uncertainties. In my talk, I will outline how statistical inference pipelines for the neutron star EoS are constructed, identify key sources of theoretical uncertainty, and discuss current limitations. Finally, I will argue that valuable clues to the behavior of matter in neutron star cores may come not only from the skies, but also from heavy-ion collision experiments here on Earth.