Synergy between CSST galaxy survey and gravitational-wave observation: Inferring the Hubble constant from dark standard sirens

Gravitational waves(GWs) from compact binary coalescences encode the absolute luminosity distances of GW sources. Once the redshifts of GW sources are known, one can use the distance-redshift relation to constrain cosmological parameters. One way to obtain the redshifts is to localize GW sources by GW observations and then use galaxy catalogs to determine redshifts from a statistical analysis of redshift information of the potential host galaxies, commonly referred to as the dark siren method. The third-generation(3G) GW detectors are planned to work in the 2030s and will observe numerous compact binary coalescences.Using these GW events as dark sirens requires high-quality galaxy catalogs from future sky survey projects. The China Space Station Telescope(CSST) will be launched in 2024 and will observe billions of galaxies within a 17500 deg^(2) survey area with redshift up to z ~ 4, providing photometric and spectroscopic galaxy catalogs. In this work, we simulate the CSST galaxy catalogs and the 5-year GW data from the 3G GW detectors and combine them to infer the Hubble constant(H_(0)). Our results show that the measurement precision of H0could reach the sub-percent level, meeting the standard of precision cosmology. We conclude that the synergy between CSST and the 3G GW detectors is of great significance in measuring the Hubble constant.

Cosmology with fast radio bursts in the era of SKA

We present a forecast of the cosmological parameter estimation using fast radio bursts(FRBs)from the upcoming Square Kilometre Array(SKA),focusing on the issues of dark energy,the Hubble constant,and baryon density.We simulate 105and 106localized FRBs from a 10-year SKA observation,and find that:(1)using 106FRB data alone can tightly constrain dark-energy equation of state parameters better than CMB+BAO+SNe,providing an independent cosmological probe to explore dark energy;(2)combining the FRB data with gravitational-wave standard siren data from 10-year observation with the Einstein Telescope,the Hubble constant can be constrained to a sub-percent level,serving as a powerful low-redshift probe;(3)using 106FRB data can constrain the baryon density?bh to a precision of~0.1%.Our results indicate that SKA-era FRBs will provide precise cosmological measurements to shed light on both dark energy and the missing baryon problem,and help resolve the Hubble tension.

太极计划的引力波标准汽笛观测将助力宇宙学参数测量

太极计划是一个引力波空间探测项目,计划发射3颗绕日轨道卫星,组成一个各自相距300万公里的等边三角形卫星组,利用激光干涉方法进行中低频波段(0.1 m Hz^1.0 Hz)引力波的直接探测.太极计划可观测由超大质量双黑洞并合产生的引力波标准汽笛事件,用于探测宇宙的膨胀历史.本文对太极计划利用标准汽笛观测提升宇宙学参数测量精度的能力进行了预测.基于3种超大质量黑洞模型对太极计划5年的标准汽笛数据进行了模拟,发现其标准汽笛数据可有效打破宇宙微波背景观测所带来的固有宇宙学参数简并,特别是对于动力学暗能量模型,这种打破参数简并的作用尤为显著.当前基于电磁观测的宇宙学探针已可以极高的精度测量宇宙学参数,即便如此,太极计划的标准汽笛观测仍能在一定程度上帮助进一步改善宇宙学参数测量,并在未来为我们提供极为重要的宇宙学探针.

Black ring entropy from the Weyl tensor

A black ring is an asymptotically fiat vacuum solution of the n-dimensional Einstein equations with an event horizon of topology S1× Sn-3. In this study, a connection between the black ring entropy and the Weyl tensor Cμνλρ is explored by interpreting the Weyl scalar invariant CμνλρCμνλρ as the entropy density in five-dimensional space-time. It is shown that the proper volume integral of CμνλρCμνλρfor a neutral black ring is proportional to the black ring entropy in the thin-ring limit. Similar calculations are extended to more general cases： a black string, a black ring with two angular momenta, and a black ring with a cosmological constant. The proportionality is also found to be valid for these complex black objects at the leading order.