Hubble constant
Pro Research Analysisby 
Searched over 200M research papers for "hubble constant"
Understanding the Hubble Constant: Current Measurements and Methods
Introduction to the Hubble Constant
The Hubble constant (H₀) is a critical parameter in cosmology, representing the rate at which the universe is expanding. Accurate measurement of H₀ helps in understanding the size, age, and ultimate fate of the universe. Despite significant advancements, there remains a notable tension between different methods of measuring H₀.
Cepheid Variables and Type Ia Supernovae
Cepheid-Based Measurements
Cepheid variables are a primary tool for measuring cosmic distances due to their well-defined period-luminosity relationship. The SH0ES team has utilized Cepheid variables in the host galaxies of Type Ia supernovae (SNe Ia) to calibrate H₀. Their comprehensive analysis, which includes data from Gaia EDR3 parallaxes, masers in NGC 4258, and detached eclipsing binaries in the Large Magellanic Cloud (LMC), yields a value of H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹ 2. This method benefits from high precision but shows a significant discrepancy with early-universe measurements.
LMC Cepheid Standards
Further refinement using LMC Cepheid standards has provided a robust foundation for H₀ determination. By leveraging the geometric distance to the LMC and improved photometric calibration, researchers have achieved a value of H₀ = 74.03 ± 1.42 km s⁻¹ Mpc⁻¹ 3. This result underscores the reliability of Cepheid-based measurements but also highlights the persistent tension with cosmic microwave background (CMB) estimates.
Tip of the Red Giant Branch (TRGB)
The TRGB method offers an independent approach to measuring H₀. By calibrating the TRGB distances using deep Hubble Space Telescope (HST) imaging and anchoring them to SNe Ia, researchers have determined H₀ = 69.8 ± 0.8 (stat) ± 1.7 (sys) km s⁻¹ Mpc⁻¹ 1. This value sits between the Cepheid-based measurements and the CMB estimates, providing a crucial cross-check.
Megamaser Cosmology
Geometric distance measurements to megamaser-hosting galaxies provide another independent method. The Megamaser Cosmology Project has refined distance estimates for several galaxies, resulting in H₀ = 73.9 ± 3.0 km s⁻¹ Mpc⁻¹ 4. This method corroborates the higher local values of H₀ and supports the notion of a discrepancy with early-universe measurements.
Gravitational Waves
Gravitational wave observations from events like GW170817 offer a novel way to measure H₀. By combining gravitational wave data with electromagnetic counterparts and radio observations, researchers have derived H₀ = 70.3⁻⁵.⁰⁺⁵.³ km s⁻¹ Mpc⁻¹ 7. This method is independent of the cosmic distance ladder and provides a promising avenue for resolving the Hubble tension.
Time-Delay Cosmography
Strongly lensed quasars and galaxies provide another method to measure H₀ through time-delay cosmography. Analysis of eight quadruply lensing systems has yielded H₀ = 71.8⁺³.⁹₋₃.³ km s⁻¹ Mpc⁻¹ 8. While this method's precision is lower, it aligns with other local measurements and adds to the body of evidence for a higher H₀.
Conclusion
The determination of the Hubble constant remains a central challenge in cosmology. Various methods, including Cepheid variables, TRGB, megamasers, gravitational waves, and time-delay cosmography, provide a range of H₀ values. The persistent discrepancy between local measurements and early-universe estimates suggests the possibility of new physics beyond the standard cosmological model. Continued efforts and new observations are essential to resolve this tension and enhance our understanding of the universe's expansion.
Sources and full results
Most relevant research papers on this topic
The Carnegie-Chicago Hubble Program. VIII. An Independent Determination of the Hubble Constant Based on the Tip of the Red Giant Branch
The Hubble constant (H0) is 69.8 0.8 km s-1 Mpc-1, midway between the Planck Collaboration and the HST SHoES measurements, with advantages over Cepheid variables.
Highly CitedA Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km s−1 Mpc−1 Uncertainty from the Hubble Space Telescope and the SH0ES Team
The Hubble constant (H 0) is 73.04 1.04 km s1 Mpc1 with systematic uncertainties, a 5 difference from Planck cosmic microwave background predictions under CDM.
Highly CitedLarge Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination of the Hubble Constant and Stronger Evidence for Physics beyond ΛCDM
The improved determination of the Hubble constant from Long-period Cepheids in the Large Magellanic Cloud reduces uncertainty from 2.5% to 1.3%, increasing the odds of a cosmological feature beyond CDM.
Highly CitedThe Megamaser Cosmology Project. XIII. Combined Hubble Constant Constraints
The Hubble constant is H0 = 73.9 3.0 km s1 Mpc1 using geometric distance measurements to megamaser-hosting galaxies, with a confidence level ranging from 95% to 99%.
Highly CitedThe Hubble constant and the expansion age of the Universe
Recent progress in measuring the Hubble constant suggests the Universe has a kinematic age of less than 142 billion years, favoring a low-matter-density universe and either an open or flat universe with a non-zero cosmological constant.
A Hubble constant measurement from superluminal motion of the jet in GW170817
This study improves the Hubble constant measurement using new radio observations of GW170817, suggesting that 15 more events with radio data could resolve the tension between Planck and Cepheid-supernova measurements.
Highly CitedThe Hubble constant from eight time-delay galaxy lenses
Current lensing constraints on the Hubble constant are not strong enough to break the "Hubble tension" problem in cosmology.
The Hubble constant.
The Hubble constant H0 = 90 +/- 10 km.s-1.Mpc-1, indicating a difficulty reconciling it with the preferred world model, and may exclude the standard model with Omega = 1.
Highly CitedHubble constant hunter’s guide
The most likely solution to reconcile the Hubble constant and cosmic microwave background data is to increase the expansion rate in the decade before recombination.
Highly Cited