A new study led by University of Illinois Urbana-Champaign physics professor Nicolas Yunes has provided new insights into the inner workings of neutron stars, shedding light on the dynamics that underpin the workings of the universe. Neutron stars are the collapsed cores of stars and are the densest stable material objects in the universe, with conditions much denser and colder than those that can be created by particle colliders. The mere existence of neutron stars points to unseen properties related to astrophysics, gravitational physics, and nuclear physics that play a critical role in the inner workings of the universe.
With the discovery of gravitational waves, many of these previously unseen properties have become observable. The properties of neutron stars can be imprinted onto the gravitational waves they emit, which then travel millions of light-years through space to detectors on Earth, such as the advanced European Laser Interferometer Gravitational-Wave Observatory and the Virgo Collaboration. By detecting and analyzing these waves, scientists can infer the properties of neutron stars and learn about their internal composition and the physics at play in their extreme environments.
As a gravitational physicist, Yunes was interested in determining how gravitational waves encode information about the tidal forces that distort the shape of neutron stars and affect their orbital motion. This information could provide insight into the dynamic material properties of the stars, such as internal friction or viscosity, which might give us insight into physical processes that result in the transfer of energy into or out of a system. Using data from the gravitational wave event GW170817, Yunes and his team used computer simulations, analytical models, and sophisticated data analysis algorithms to verify that out-of-equilibrium tidal forces within binary neutron star systems are detectable via gravitational waves.
While the GW170817 event was not loud enough to yield a direct measurement of viscosity, Yunes’ team was able to place the first observational constraints on how large viscosity can be inside neutron stars. The study findings have been published in the journal Nature Astronomy, marking an important advance for the Illinois Center for Advanced Studies of the Universe (ICASU) and the University of Illinois. With access to data from advanced LIGO and Virgo detectors and collaborations made possible through ICASU, Illinois continues its legacy of pioneering theories in nuclear physics, particularly those connected to neutron stars.
The University of Illinois Graduate College Dissertation Completion Fellowship and the National Science Foundation supported this study, highlighting the importance of continued research into the inner workings of neutron stars and the implications for our understanding of the universe. A better understanding of neutron stars not only informs our knowledge of astrophysics, gravitational physics, and nuclear physics but also has practical applications that could drive future technology developments. By studying the information encoded in gravitational waves from neutron stars, scientists can gain valuable insights into the dynamics at play in the extreme environments of these collapsed cores of stars.