Measurements of the redshift alone enable crucial investigations of how the luminosity distance relates to redshift this relationship in turn allows us to probe cosmological models. However, measurements of the characteristic frequencies before and after the merger, together with prior knowledge of their true values from numerical simulations, allow us to break the mass-redshift degeneracy and extract the redshift directly from gravitational-wave observations. Until recently, it was thought that gravitational-wave observations alone cannot determine this redshift since a degeneracy exists between the merger’s mass and its redshift: Only the redshifted mass- M ( 1 + z )-is measured. The expansion of the Universe redshifts the gravitational-wave frequencies, and the observed frequencies are lower in proportion to how fast the sources are moving away from us. Our numerical modeling has allowed us to identify characteristic frequencies in the gravitational wave signal from the merged object, i.e., the short-lived hypermassive neutron star. To accurately model the dynamics of such systems and to compute the emitted gravitational radiation, we rely on cutting-edge numerical relativity simulations.
Some of the most likely sources of gravitational radiation are inspiraling binary neutron stars upcoming detectors should be able to detect approximately ten merger events per year. There is currently a global effort underway to detect this radiation from astrophysical sources. We find that for a known illustrative neutron star equation of state and using the Einstein telescope, the median of the 1 σ confidence regions in redshift corresponds to ∼ 10 % – 20 % uncertainties at redshifts of z < 0.04.Īccording to Einstein’s theory of general relativity, the acceleration of mass leads to the emission of energy in the form of gravitational radiation. Using numerical simulations of binary neutron star mergers of different mass, we model gravitational-wave signals at different redshifts and use a Bayesian parameter estimation to determine the accuracy with which the redshift and mass can be extracted. The entirety of this analysis method and any subsequent cosmological inference derived from it would be obtained solely from gravitational-wave observations and, hence, would be independent of the cosmological distance ladder. Here, we propose to use the signature encoded in the postmerger signal allowing the accurate extraction of the intrinsic rest-frame mass of the source, in turn permitting the determination of source redshift and luminosity distance. Recent work has shown that for third-generation detectors, a tidal correction to the gravitational-wave phase in the late-inspiral signal of binary neutron star systems can be used to break the mass-redshift degeneracy. However, a degeneracy in the information carried by gravitational waves between the total rest-frame mass M and the redshift z of the source implies that neither can be directly extracted from the signal only the combination M ( 1 + z ), the redshifted mass, can be directly extracted from the signal. Inspiraling compact binaries as standard sirens will become an invaluable tool for cosmology when we enter the gravitational-wave detection era.