It is currently unknown how matter behaves at the extreme densities found
within the cores of neutron stars. Measurements of the neutron star equation of
state probe nuclear physics that is otherwise inaccessible in a laboratory
setting. Gravitational waves from binary neutron star mergers encode details
about this physics, allowing the equation of state to be inferred. Planned
third-generation gravitational-wave observatories, having vastly improved
sensitivity, are expected to provide tight constraints on the neutron star
equation of state. We combine simulated observations of binary neutron star
mergers by the third-generation observatories Cosmic Explorer and Einstein
Telescope to determine future constraints on the equation of state across a
plausible neutron star mass range. In one year of operation, a network
consisting of one Cosmic Explorer and the Einstein Telescope is expected to
detect $gtrsim 3times 10^5$ binary neutron star mergers. By considering only
the 75 loudest events, we show that such a network will be able to constrain
the neutron star radius to at least $lesssim 200$ m (90% credibility) in the
mass range $1-1.97$ $M_{odot}$ — about ten times better than current
constraints from LIGO-Virgo-KAGRA and NICER. The constraint is $lesssim 75$ m
(90% credibility) near $1.4-1.6$ $M_{odot}$ where we assume the the binary
neutron star mass distribution is peaked. This constraint is driven primarily
from the loudest $sim 20$ events.

Future Roadmap: Challenges and Opportunities for Understanding Neutron Stars

Neutron stars, with their extreme densities, continue to be a mystery in our understanding of matter. However, recent advancements in gravitational wave detection have provided an opportunity to probe the equations of state of these neutron stars. The upcoming third-generation gravitational-wave observatories, such as Cosmic Explorer and Einstein Telescope, are expected to bring us closer to unlocking the secrets of neutron star physics.


  • The third-generation observatories will have significantly improved sensitivity compared to the current detectors.
  • These observatories will be able to detect over 300,000 binary neutron star mergers in just one year.
  • By analyzing the loudest 75 events, we can expect to obtain tight constraints on the neutron star radius.
  • The constraints on the neutron star equation of state will be at least 10 times better than current measurements from LIGO-Virgo-KAGRA and NICER.
  • The constraints will be especially strong in the mass range of 1-1.97 solar masses, where the neutron star mass distribution is peaked.


  • Understanding how matter behaves at extreme densities within neutron stars remains unknown.
  • Simulating observations and accurately interpreting the gravitational wave data require advanced computational techniques.
  • The vast amount of data collected by the third-generation observatories will require efficient data analysis methods.

Overall, the future looks promising for understanding the physics of neutron stars. With the improved sensitivity of third-generation observatories and their ability to detect a large number of binary neutron star mergers, we can anticipate significant advancements in our knowledge of neutron star equations of state. The constraints obtained will provide crucial insights into the nature of matter under extreme conditions and contribute to our broader understanding of nuclear physics.

Reference: Excerpt from “Future Constraints on Neutron Star Physics from Third-Generation Gravitational-Wave Observatories” by [Authors]

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