A two per cent Hubble constant measurement from standard sirens within five years

Area of Science:

• Cosmology
• Astrophysics
• Gravitational-wave astronomy

Background:

• The Hubble constant (H0) measures the universe's expansion rate.
• Current H0 measurements from local (supernovae) and early universe (CMB) data show a significant tension (~3σ).
• Gravitational-wave (GW) astronomy offers an independent method to measure H0.

Purpose of the Study:

• To assess the potential of future gravitational-wave detections for constraining the Hubble constant.
• To investigate how GW standard sirens can help resolve the current H0 discrepancy.
• To explore the implications of precise H0 measurements for understanding dark energy.

Main Methods:

• Utilizing the 'standard siren' method with binary neutron star mergers detected by LIGO and Virgo.
• Combining GW data with electromagnetic observations to identify host galaxies and determine luminosity distances.
• Analyzing the expected precision of H0 measurements from future GW event rates.

Main Results:

• The standard siren method using GW170817 provided an independent H0 measurement.
• Future GW detections are projected to constrain H0 to ~2% precision within 5 years and ~1% within a decade.
• This precision will be independent of systematics affecting other H0 measurement techniques.

Conclusions:

• Gravitational-wave detections offer a powerful, independent probe of the Hubble constant.
• Continued observations will significantly reduce the H0 tension, providing crucial insights into cosmology.
• Precise H0 measurements are vital for advancing our understanding of dark energy and the universe's evolution.