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First measurement of the Hubble constant from a combined weak lensing and gravitational-wave standard siren analysis

This paper presents the first joint analysis of Dark Energy Survey Year 3 weak lensing and galaxy clustering data with LIGO-Virgo-KAGRA gravitational-wave standard sirens, yielding a 6.4% precision measurement of the Hubble constant ( $H_0 = 67.9^{+4.4}_{-4.3}$ km s $^{-1}$ Mpc $^{-1}$ ) and demonstrating that combining these distinct cosmological probes is a viable path toward resolving the current Hubble tension.

Original authors: Felipe Andrade-Oliveira, David Sanchez-Cid, Danny Laghi, Marcelle Soares-Santos

Published 2026-05-13

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CC BY 4.0

Original authors: Felipe Andrade-Oliveira, David Sanchez-Cid, Danny Laghi, Marcelle Soares-Santos

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Problem: The Universe's Speedometer is Broken

Imagine the universe is a car, and scientists are trying to figure out exactly how fast it is speeding up as it expands. This speed is called the Hubble Constant ( $H_0$ ).

The problem is that the universe's "speedometer" is giving two very different readings:

The Early Universe Reading: By looking at the "baby photos" of the universe (the Cosmic Microwave Background), scientists calculate one speed.
The Late Universe Reading: By looking at "adult photos" (exploding stars and nearby galaxies), scientists calculate a faster speed.

These two numbers don't match, and the difference is so big that it suggests our current understanding of the universe's rules (physics) might be missing something. This is known as the "Hubble Tension."

The New Solution: A Two-Tool Approach

This paper introduces a new way to measure the speed of the universe by combining two very different tools, like using both a ruler and a sonar to measure the distance to a ship.

Tool 1: The "Cosmic Ruler" (Weak Lensing & Galaxy Clustering)

What it is: The team used data from the Dark Energy Survey (DES). They looked at millions of galaxies.
How it works: Imagine looking at a distant object through a wavy glass window. The glass (gravity from dark matter) distorts the image. By measuring how much the shapes of galaxies are stretched and how they cluster together, scientists can map out the "wavy glass" and figure out how much stuff (matter) is in the universe.
The Paper's Claim: This method alone gives a decent estimate, but it has a bit of fuzziness (about 17% uncertainty).

Tool 2: The "Cosmic Sonar" (Gravitational Waves)

What it is: The team used data from the LIGO-Virgo-KAGRA (LVK) collaboration. They listened for "chirps" caused by black holes or neutron stars crashing into each other.
How it works: When these objects crash, they send out ripples in space-time (gravitational waves). The loudness of the "chirp" tells us exactly how far away the crash happened. This is called a "Standard Siren" because, unlike a regular siren whose volume you don't know, we know exactly how loud these crashes should be.
The Paper's Claim: This method is great at measuring distance but usually struggles to tell us where the crash happened in time (redshift) without help.

The Secret Ingredient: The "Superluminal Jet"

For one specific crash called GW170817, the team had a special advantage.

The Analogy: Imagine you hear a siren (the gravitational wave) but can't see the source. Suddenly, you see a jet of water shooting out of the source at incredible speed. By watching how that jet moves, you can figure out exactly how the source is tilted and how far away it is.
The Paper's Claim: By using observations of a "superluminal jet" (a jet moving faster than light appears to move due to geometry) from the aftermath of GW170817, they got a much sharper angle on the distance. Without this jet info, the measurement gets much fuzzier.

The Result: Putting the Puzzle Together

The team combined the "Cosmic Ruler" (DES data) and the "Cosmic Sonar" (Gravitational Wave data) into one giant calculation.

The Outcome: They calculated the Hubble Constant to be 67.9 km/s/Mpc with a precision of 6.4%.
Why it matters:
- This is the first time these two specific methods (weak lensing and gravitational waves) have been combined to measure this speed.
- It confirms that the "Ruler" and the "Sonar" agree with each other (they are consistent).
- It improved the measurement of the universe's total matter ( $\Omega_m$ ) by 22%.
- If they removed the "jet" information from GW170817, the precision would have dropped significantly (to 9.9%), proving that the jet data was a crucial piece of the puzzle.

The Bottom Line

This paper doesn't solve the "Hubble Tension" (the disagreement between early and late universe measurements) yet. Instead, it proves that combining different types of cosmic data works.

Think of it like a detective solving a case. One witness (the Ruler) gives a good description, and another witness (the Sonar) gives a different but compatible description. When they testify together, the picture becomes much clearer. The authors say that as we get more data from future telescopes and gravitational wave detectors, this combined approach will help us pin down the universe's expansion rate with even greater accuracy, potentially helping us understand why the speedometer is broken in the first place.

Technical Summary: First Measurement of the Hubble Constant from a Combined Weak Lensing and Gravitational-Wave Standard Siren Analysis

Problem Statement
The measurement of the Hubble constant ( $H_0$ ) remains a central empirical challenge in cosmology, characterized by a significant ( $\gtrsim 5\sigma$ ) tension between values inferred from early-Universe cosmic microwave background (CMB) data under the $\Lambda$ CDM assumption and direct late-Universe measurements using the cosmic distance ladder (e.g., Type Ia supernovae). While numerous analyses have attempted to reconcile these discrepancies by identifying systematic effects, the problem persists. This work addresses the need for independent, multi-messenger approaches that do not rely on the cosmic distance ladder to constrain $H_0$ .

Methodology
The authors present a joint cosmological analysis combining two distinct observational frameworks:

3 $\times$ 2pt Analysis (Weak Lensing & Galaxy Clustering): Utilizing data from the Dark Energy Survey (DES) Year 3 (Y3) release, the study employs three two-point correlation functions (2PCFs): cosmic shear (shear-shear), galaxy clustering (galaxy-galaxy), and the cross-correlation of galaxy shear and position (galaxy-shear). This framework constrains the matter abundance ( $\Omega_m$ ) and the amplitude of matter density fluctuations. The analysis incorporates source galaxy shapes (approx. 100 million galaxies in four redshift bins) and lens galaxies (MagLim sample, 10.7 million galaxies in six redshift bins), accounting for systematic effects such as galaxy bias, intrinsic alignment, and redshift calibration.
Standard Sirens Analysis: The study integrates data from the Gravitational-Wave Transient Catalog 4.0 (GWTC-4.0) released by the LIGO-Virgo-KAGRA (LVK) Collaboration.
- Spectral Sirens: For 141 compact binary coalescence (CBC) events, redshift information is derived exclusively from the mass spectrum of the binary population using Bayesian hierarchical inference, avoiding reliance on galaxy catalogs to prevent covariance systematic errors.
- Bright Siren (GW170817): For the single event with a confirmed electromagnetic (EM) counterpart, the analysis incorporates host galaxy redshift (NGC 4993) and, crucially, inclination angle constraints derived from superluminal jet observations. The inclination angle ( $15^\circ < \theta_{jet} < 29^\circ$ ) is used as an external prior to refine the luminosity distance ( $d_L$ ) estimation.

Cosmological Inference
The authors combine posterior distributions from the DES Y3 3 $\times$ 2pt analysis and the LVK standard siren analysis (141 spectral sirens + 1 bright siren). Assuming independence between the datasets, they utilize a normalizing flow method (implemented in tensiometer) to merge the posteriors. The analysis marginalizes over nuisance parameters while inferring the cosmological parameters $s_c = \{H_0, \Omega_m\}$ , adopting broad priors ( $H_0 \in [10, 200]$ km s $^{-1}$ Mpc $^{-1}$ , $\Omega_m \in [0, 1]$ ) to match the spectral siren analysis requirements.

Key Results

Combined Measurement: The joint analysis yields a Hubble constant of $H_0 = 67.9^{+4.4}_{-4.3}$ km s $^{-1}$ Mpc $^{-1}$ , representing a 6.4% precision measurement.
Impact of Jet Information: The inclusion of the jet inclination angle for GW170817 is critical. Removing this information degrades the standard siren-only precision to 15% and the combined precision to 9.9%.
Constraining Power on $\Omega_m$ : While the standard siren component alone provides no significant constraint on $\Omega_m$ , the combination with 3 $\times$ 2pt improves the precision of the total matter abundance measurement by 22% (from 11% to 8.2%) relative to the fiducial DES Y3 analysis.
Consistency: The $H_0$ posteriors from the 3 $\times$ 2pt and standard siren components are found to be in good agreement, with a distance of 0.78 $\sigma$ between their medians.

Significance and Claims
The paper claims to present the first measurement of the Hubble constant resulting from a joint analysis of standard sirens and weak gravitational lensing/galaxy clustering observables. The authors demonstrate that incorporating standard sirens into the multi-probe cosmology framework of large cosmic surveys is a viable route to constrain $H_0$ without relying on the cosmic distance ladder.

The study highlights that this combined approach offers a complementary path to resolving the $H_0$ tension. The authors note that with impending new data releases from DES and LVK, and the anticipated constraining power of future 3 $\times$ 2pt observables from newly commissioned instruments, this methodology represents a promising avenue for achieving percent-level precision on $H_0$ and advancing the field of cosmology. The results suggest that standard sirens possess sufficient constraining power to be informative when combined with traditional large-scale structure probes, similar to the role played by CMB, SNe Ia, or baryon acoustic oscillations.

The Big Problem: The Universe's Speedometer is Broken

The New Solution: A Two-Tool Approach

The Secret Ingredient: The "Superluminal Jet"

The Result: Putting the Puzzle Together

The Bottom Line

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