Measuring the Hubble Constant of Binary Neutron Star and Neutron Star–Black Hole Coalescences: Bright Sirens and Dark Sirens

Abstract

Observations of gravitational waves (GW) provide us with a new probe to study the Universe. GW events can be used as standard sirens if their redshifts are measured. Normally, standard sirens can be divided into bright/dark sirens according to whether the redshifts are measured by electromagnetic (EM) counterpart observations. First, we investigate the capability of the 2.5 m Wide-Field Survey Telescope (WFST) to take follow-up observations of kilonova counterparts. For binary neutron star (BNS) bright sirens, WFST is expected to observe 10–20 kilonovae per year in the second-generation GW detection era. As for neutron star–black hole (NSBH) mergers, when a BH spin is extremely high and the neutron star (NS) is stiff, the observation rate is ∼10 per year. Combining optical and GW observations, the bright sirens are expected to constrain the Hubble constant H 0 to ∼2.8% in five years of observations. As for dark sirens, the tidal effects of NSs during merging provide us with a cosmological model-independent approach to measure the redshifts of GW sources. Then we investigate the applications of tidal effects in redshift measurements. We find in the third generation era, the host galaxy groups of around 45% BNS mergers at z < 0.1 can be identified through this method, if the equation of state is ms1, which is roughly equivalent to the results from luminosity distant constraints. Therefore, tidal effect observations provide a reliable and cosmological model-independent method of identifying BNS mergers’ host galaxy groups. Using this method, the BNS/NSBH dark sirens can constrain H 0 to 0.2%/0.3% over a five-year observation period.

Can the late dark energy parameterization reconcile the Hubble tension?*

“…[47], future thousands of fast radio bursts could achieve a 3% precision on the random error of the Hubble constant. Gravitational waves and strong gravitational lensing can play an important role in exploring cosmological tensions [48][49][50][51]. Using observations of the tidal effect, the BNS/NSBH dark sirens can constrain to 0.2%/0.3% over a five-year observation period [52].…”

Forecast cosmological constraints from the number counts of Gravitational Waves events

“…In the rare case where we can measure the redshift of the binary through the GWs electromagnetic counterpart, we call these events Standard Sirens or Bright Sirens as opposed to Dark Sirens where z has to be found with alternative techniques. Furthermore, Dark Sirens can be classified as a function of the method used to find z: Statistical Sirens, where the sky patch localized by GW events is scanned for galaxies or galaxy clusters whose redshifts are combined to obtain the most likely value of the true redshift [6][7][8][9]; Spectral Sirens, where the independence of the mass spectrum distribution from redshift can be exploited to break the mass-redshift degeneracy [10]; Love Sirens, where source frame masses of a neutron star binary system are obtained from the direct measurement of its tidal deformability, hence breaking again the mass-redshift degeneracy [11][12][13][14][15][16]; Gray Sirens, when a BH-NS system is doubly used as a Dark Siren and as a Bright Siren [17]; and finally we mention a term often used: Golden Sirens, i.e. well localized single event Dark Sirens such that the resulting Hubble constant estimate can resolve the Hubble tension (i.e.…”