How Gravitational Waves Reveal Neutron Star Mysteries

Understanding the inner workings of neutron stars can greatly enhance our grasp of cosmic dynamics and potentially drive future technologies, according to Nicolas Yunes, a physics professor at the University of Illinois Urbana-Champaign. Yunes leads a new study that explores how insights into dissipative tidal forces within binary neutron star systems could deepen our knowledge of the universe.

Neutron stars are the remnants of collapsed stars and are among the densest objects in the universe, far denser and colder than conditions in particle colliders, as noted by Yunes, who is also the founding director of the Illinois Center for Advanced Studies of the Universe (ICASU). The existence of neutron stars suggests the presence of hidden properties related to astrophysics, gravitational physics, and nuclear physics that are crucial for understanding the universe.

Many of these hidden properties became detectable with the advent of gravitational waves. These waves, which travel millions of light-years through space, carry information about the properties of neutron stars. By analyzing these waves with instruments like the European Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo Collaboration, scientists can infer details about neutron stars' internal composition and the extreme physics within them.

Yunes, a specialist in gravitational physics, focused on how gravitational waves reveal information about tidal forces that deform neutron stars and influence their orbital movements. These tidal forces also provide clues about the stars' material properties, such as internal friction or viscosity. Understanding these out-of-equilibrium physical processes could offer insights into how energy is transferred within these systems.

Using data from the gravitational wave event GW170817, Yunes and his team, including researchers Justin Ripley, Abhishek Hegade, and Rohit Chandramouli, employed computer simulations, analytical models, and advanced data analysis techniques to confirm that out-of-equilibrium tidal forces in binary neutron star systems can be detected through gravitational waves. Although GW170817 was not intense enough to measure viscosity directly, the team established the first observational limits on how significant viscosity can be within neutron stars.

This research, published in Nature Astronomy, marks a significant advancement for ICASU and the University of Illinois. Yunes highlighted that the institution's past achievements in nuclear physics, particularly regarding neutron stars, can continue with the help of advanced detectors and ongoing collaborations facilitated by ICASU.