Neutron Star Measurements Place Limits on Color Superconductivity in Dense Quark Matter

Requiring consistency between the physics of neutron stars and quark matter leads to the first astrophysical constraint on this exotic phase of matter.

Ground-based radio telescopes, gravitational wave detectors, and a space-based X-ray telescope (right) all measure neutron stars (top left, shown merging), lending insight into the pairing of different-colored quarks in dense matter (bottom left).
Image courtesy of Rachel Steinhorst, NASA/Roscosmos, and Caltech/MIT/LIGO Lab
Ground-based radio telescopes, gravitational wave detectors, and a space-based X-ray telescope (right) all measure neutron stars (top left, shown merging), lending insight into the pairing of different-colored quarks in dense matter (bottom left).

The Science

At extremely high densities, quarks are expected to form pairs, as electrons do in a superconductor. This high-density quark behavior is called color superconductivity. The strength of pairing inside a color superconductor is difficult to calculate, but scientists have long known the strength’s relationship to the pressure of dense matter. Measuring the size of neutron stars and how they deform during mergers tells us their pressure and confirms that neutron stars are indeed the densest visible matter in the universe. In this study, researchers used neutron star observations to infer the properties of quark matter at even higher densities where it is certain to be a color superconductor. This yields the first empirical upper bound on the strength of color superconducting pairing.

The Impact

Theoretical physicists have studied color superconductivity for more than two decades. However, this study’s connection to neutron star observations is the first ever empirical limit on the pairing strength of color superconductors. This opens a new research frontier for using the astrophysics of neutron stars to learn about the physics of quark matter.

Summary

Measurements from NICER, LIGO/Virgo, and ground-based radio telescopes provide insight into the pressures and densities at the cores of various neutron stars, each with some uncertainty. In this study, researchers performed a statistical analysis of these measurements to extract a range of possible pressures at quark-matter densities. Scientists know what the pressure of quark matter at these high densities would be without considering quark pairing, so the range of possible deviation from that baseline provided this study’s researchers with the range of pairing effects that are consistent with the neutron star observations. This allowed the researchers to extract empirical bounds on the strength of color superconducting pairing.

Contact

Rachel Steinhorst
Massachusetts Institute of Technology
rstein99@mit.edu

Funding

This work was supported by the Department of Energy Office of Science, Office of Nuclear Physics.

Publications

Kurkela, A., Rajagopal, K., and Steinhorst, R., Astrophysical Equation-of-State Constraints on the Color-Superconducting Gap. Physical Review Letters 132, 262701 (2024). [DOI: 10.1103/PhysRevLett.132.262701]

Highlight Categories

Program: NP

Performer: University