Value of hubble's constant
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Determining the Value of Hubble's Constant: A Comprehensive Overview
Introduction to Hubble's Constant
Hubble's constant (H₀) is a critical parameter in cosmology, representing the rate of expansion of the universe. Despite its importance, there is significant debate and variation in its measured value, leading to what is known as the "Hubble tension."
Tip of the Red Giant Branch (TRGB) Method
A recent study using the TRGB method has provided a value of H₀ = 69.8 ± 0.8 (stat) ± 1.7 (sys) km s⁻¹ Mpc⁻¹. This method is independent of the Cepheid distance scale and offers several advantages, such as low halo reddening and minimal effects of crowding or blending of the photometry1. The TRGB method's value sits midway in the range defined by the current Hubble tension, aligning closely with the Planck Collaboration's estimate and the Hubble Space Telescope (HST) SHoES measurement1.
Cepheid Variables and Type Ia Supernovae
The SH0ES team has utilized Cepheid variables in the host galaxies of Type Ia supernovae (SNe Ia) to determine H₀. Their comprehensive analysis, which includes data from over 1,000 HST orbits, yields a value of H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹3. This value is consistent with other measurements using Cepheid variables and SNe Ia, further supporting the higher end of the Hubble constant spectrum3.
Large Magellanic Cloud (LMC) Cepheid Standards
Another significant contribution comes from the improved determination of H₀ using LMC Cepheid standards. This method, which combines data from detached eclipsing binaries and refined calibration techniques, results in H₀ = 74.03 ± 1.42 km s⁻¹ Mpc⁻¹4. This value is notably higher than the TRGB method and aligns with the SH0ES team's findings, suggesting a potential systematic difference in measurement techniques4.
Megamaser Cosmology Project
The Megamaser Cosmology Project provides an independent measurement of H₀ using geometric distance measurements to megamaser-hosting galaxies. Their findings suggest H₀ = 73.9 ± 3.0 km s⁻¹ Mpc⁻¹, corroborating the higher local values of H₀ and indicating a significant discrepancy with early-universe measurements5.
Evolution of Hubble's Constant
Studies investigating the evolution of H₀ with redshift, such as those using the SNe Ia Pantheon sample and Baryon Acoustic Oscillations, suggest a decreasing trend in H₀ with redshift. This trend, if confirmed, could imply hidden astrophysical biases or necessitate new theoretical models, such as modified gravity theories2 8.
Most Frequent Value (MFV) Statistics
An alternative approach using MFV statistics has calculated H₀ to be 67.498 km s⁻¹ Mpc⁻¹, closely aligning with the Planck measurements and suggesting a lower value for H₀7. This method emphasizes the robustness of statistical analysis regardless of the distribution of original measurements7.
Time-Delay Galaxy Lenses
Time-delay cosmography using strongly lensing systems provides another independent measurement of H₀. A recent study determined H₀ = 71.8⁺³.⁹₋₃.³ km s⁻¹ Mpc⁻¹, which is consistent with both local and early-universe measurements but does not resolve the Hubble tension9.
Conclusion
The value of Hubble's constant remains a topic of active research and debate. Different methods yield varying results, with local measurements generally suggesting higher values (around 73-74 km s⁻¹ Mpc⁻¹) and early-universe measurements indicating lower values (around 67-68 km s⁻¹ Mpc⁻¹). The ongoing discrepancy, known as the Hubble tension, highlights the need for further investigation and potentially new physics to reconcile these differences.
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 CitedOn the Evolution of the Hubble Constant with the SNe Ia Pantheon Sample and Baryon Acoustic Oscillations: A Feasibility Study for GRB-Cosmology in 2030
The Hubble constant shows a decreasing trend with 102 in the Pantheon sample, potentially due to hidden astrophysical biases or new theoretical models.
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 CitedMost Frequent Value Statistics and the Hubble Constant
The most frequent value (MFV) procedure effectively determines the Hubble constant (H0) regardless of the original measurement distribution, providing a close estimate to recent Planck and Dark Energy Survey results.
On the Hubble Constant Tension in the SNe Ia Pantheon Sample
The Hubble constant tension between Type Ia supernovae and Planck measurements has been reduced by 54% to 72%, potentially due to astrophysical selection effects or modified gravity.
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