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The road to $H_0$ , $\Omega_m$ , and $w$ with a global neutrino-telescope network

This paper forecasts that by 2030, a global network of neutrino telescopes (IceCube, KM3NeT-ARCA, and Baikal-GVD) will significantly refine the neutrino-based measurement of the Hubble constant, confirm the non-calorimetric nature of the neutrino-X-ray luminosity relation, and potentially enable independent determinations of cosmological parameters $\Omega_m$ and $w$ using high-redshift neutrino sources.

Original authors: Pavel Zhelnin, Gonzalo Herrera, Nicholas Kamp, Carlos A. Argüelles

Published 2026-10-12

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CC BY 4.0

Original authors: Pavel Zhelnin, Gonzalo Herrera, Nicholas Kamp, Carlos A. Argüelles

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 universe is expanding, but astronomers cannot agree on how fast. One method, looking at the afterglow of the Big Bang, suggests a specific speed. Another method, measuring the distances to nearby exploding stars, suggests a faster one. This disagreement, known as the Hubble tension, is one of the most pressing mysteries in modern cosmology. To solve it, scientists need a completely new way to measure cosmic distances, one that relies on different assumptions and avoids the potential errors of existing methods. For decades, high-energy neutrinos—ghostly particles that zip through the universe almost untouched by matter—have been a tantalizing possibility for such a tool, but they have been too faint and too rare to provide a clear answer.

A new study proposes a way to turn these elusive particles into a precise cosmic ruler. By combining data from a global network of neutrino detectors with observations of X-rays from active galaxies, researchers have mapped out a path to measure the expansion rate of the universe with much greater accuracy than ever before. The work suggests that by 2030, a coordinated effort between telescopes in the Arctic, the Mediterranean, and the Antarctic could pin down the expansion rate to within a few percent. More than just a number, this approach offers a fresh perspective on the invisible forces shaping the cosmos, potentially revealing new details about the density of matter and the nature of dark energy.

The key to this new method lies in a surprising connection between two very different types of light. Active galaxies, specifically a type called Seyfert galaxies, are powered by supermassive black holes at their centers. As gas swirls into these black holes, it heats up and emits X-rays. At the same time, the violent environment accelerates particles to create high-energy neutrinos. Recent observations have revealed a consistent pattern: the brighter a galaxy is in X-rays, the more neutrinos it produces. This relationship acts like a standard candle. If scientists know how much X-ray light a galaxy should emit based on its neutrino output, they can compare that predicted brightness to what is actually seen. Because light and neutrinos travel at the same speed and are not dimmed by intervening dust over these vast distances, any difference in brightness tells them exactly how far away the galaxy is.

Until now, this method has been limited by the number of galaxies we can see and the precision of our instruments. The current study takes the first successful measurement of this technique and projects how it will improve over the next few years. The researchers started with data from IceCube, a massive neutrino detector buried in the ice of Antarctica. They combined this with a new analysis of southern-sky galaxies, which were previously difficult to observe because they appear below the horizon for the Antarctic detector. By adding data from two other major detectors, KM3NeT in the Mediterranean Sea and Baikal-GVD in Lake Baikal, the team created a global network that can see the entire sky.

The results of this global network are striking. The current measurement of the universe's expansion rate, known as the Hubble constant, has a large margin of error, ranging widely. The new analysis, using existing data, refines this with a central value of 66. Looking ahead to 2030, when the new detectors are fully operational and more data is collected, the uncertainty is expected to shrink dramatically. The forecast suggests the measurement will tighten, with a central value of 66. This represents a reduction in uncertainty of nearly two-thirds, bringing the neutrino-based measurement into much sharper focus.

Alongside the expansion rate, the study also clarifies the relationship between the X-ray and neutrino emissions. The data points to a specific mathematical slope that describes how the two types of light scale with each other. The current data suggests this slope is about 0.72, meaning the neutrino output grows more slowly than the X-ray output. By 2030, the researchers project they will be able to measure this slope with such precision that they can definitively rule out a simpler, "calorimetric" model where the two would grow at the same rate. This confirmation of the specific slope is crucial because it validates the physical model used to turn the neutrino counts into distance measurements.

The power of this network extends beyond just measuring how fast the universe is expanding today. The researchers propose that if this same relationship holds true for a population of very distant, high-redshift galaxies—specifically a class of compact, red objects recently discovered by the James Webb Space Telescope—these neutrinos could be used to probe the history of the universe's expansion. By extending the distance ladder to these faraway sources, the neutrino network could provide independent measurements of the density of matter in the universe and the properties of dark energy, the mysterious force driving the accelerated expansion. While this future application relies on the assumption that these distant objects follow the same rules as nearby galaxies, the potential to test these fundamental cosmological parameters with a new type of cosmic messenger is a significant step forward.

Achieving these results will require close cooperation between the neutrino and X-ray communities. The accuracy of the distance measurements depends heavily on knowing the exact X-ray brightness of a few key "anchor" galaxies. Improving the models that account for how gas absorbs X-rays in these galaxies, and dedicating more telescope time to observing them, will be just as important as building better neutrino detectors. The path to a clearer understanding of the universe's expansion is not just about catching more particles; it is about refining the entire chain of observation, from the absorption of light in distant galaxies to the detection of ghostly particles on Earth. As the global network comes online in the coming decade, it promises to transform neutrinos from rare curiosities into a robust, independent tool for mapping the cosmos.

Technical Summary: The Road to $H_0$ , $\Omega_m$ , and $w$ with a Global Neutrino-Telescope Network

Problem and Motivation
Modern cosmology faces a $\sim 5\sigma$ tension between the Hubble constant ( $H_0$ ) inferred from early-universe observations by Planck ( $67.4 \pm 0.5$ km s $^{-1}$ Mpc $^{-1}$ ) and local measurements by SH0ES ( $73.0 \pm 1.0$ km s $^{-1}$ Mpc $^{-1}$ ). Resolving this discrepancy requires independent measurements of the expansion rate that rely on distinct assumptions and systematic error sources. High-energy neutrinos from Seyfert galaxies offer a novel "neutrino distance ladder." Recent work established a power-law relationship between the neutrino and X-ray luminosities of these sources ( $L_\nu \propto L_X^\beta$ ), allowing them to function as standardizable candles. Because neutrinos and X-rays travel unimpeded over megaparsec distances, this method avoids in-transit systematics common to other distance ladders, confining uncertainties primarily to source calibration and anchor distances.

Methodology
This study extends the initial neutrino-based $H_0$ measurement by Herrera et al. [6] through three primary avenues:

Current Data Analysis (2026 Configuration): The authors analyze an all-sky sample of 26 Seyfert galaxies (12 northern, 14 southern) using IceCube's 14-year public data release. The analysis utilizes a two-dimensional likelihood surface for each source to constrain the spectral index $\gamma$ and the luminosity relation parameters. The distance scale is anchored by two galaxies with redshift-independent distances: NGC 1068 (Cepheid distance) in the north and NGC 4945 (Tip-of-the-Red-Giant-Branch distance) in the south.
2030 Forecast: The authors project the sensitivity of a global network comprising IceCube, KM3NeT-ARCA, and Baikal-GVD by 2030. Key assumptions include:
- Full operational status of KM3NeT and Baikal-GVD.
- Improved X-ray calibration for anchor galaxies.
- A factor-of-two gain in per-source signal efficiency due to reconstruction improvements.
- Reduction of peculiar velocity uncertainties by a factor of 2.5.
- Expansion of the anchor set to five sources (adding NGC 5643, NGC 4151, and NGC 7469).
- Injection of Asimov data based on the current best-fit relation ( $H_0 = 66$ , $\beta = 0.72$ ) to simulate detector performance.
High-Redshift Extension: The paper proposes a method to measure the matter density ( $\Omega_m$ ) and dark energy equation-of-state parameter ( $w$ ) by extending the distance ladder to high-redshift populations, specifically the "little red dots" observed by JWST ( $z \sim 4-7$ ). This involves comparing the aggregate diffuse neutrino flux from these sources against predictions derived from their redshift distribution.

Key Results

Current Measurement (2026): Using existing IceCube data and the two-anchored sample, the study yields $H_0 = 66^{+44}_{-37}$ km s $^{-1}$ Mpc $^{-1}$ and a disk–corona slope $\beta = 0.72^{+0.14}_{-0.16}$ . This result is consistent with both Planck and SH0ES but remains uncertain at the $\sim 70\%$ level.
2030 Forecast: The inclusion of KM3NeT-ARCA and Baikal-GVD significantly enhances sensitivity to southern-sky sources, which are currently buried under atmospheric muon backgrounds in IceCube's down-going view. By 2030, the network is projected to:
- Sharpen the $H_0$ measurement to $66^{+15}_{-13}$ km s $^{-1}$ Mpc $^{-1}$ , a nearly 65% reduction in uncertainty.
- Pin the slope $\beta$ to $\pm 0.04$ ( $\beta = 0.72 \pm 0.04$ ). This precision enables a $\ge 5\sigma$ exclusion of the calorimetric value $\beta = 1$ .
- Detect southern sources such as NGC 4945 with a signal-to-noise ratio of $\sim 20$ , and others like Centaurus A and Circinus with ratios of 7–12.
Dark Energy Constraints: If the "little red dots" obey the same luminosity relation as Seyferts, the authors perform a Fisher forecast indicating that this high-redshift population could constrain $\Omega_m$ to $\sigma(\Omega_m) \approx 0.14$ and $w$ to $\sigma(w) \approx 1.0$ . The contours for these parameters exhibit a negative correlation, distinct from the positive correlation found in CMB constraints, due to the different redshift baselines probed.

Significance and Claims
The paper claims that a global neutrino-telescope network will transform the neutrino distance ladder into a competitive probe for the Hubble constant by 2030, offering an independent check on the $H_0$ tension. The method's significance lies in its unique systematic profile: it relies on X-ray source calibration and anchor distances but is free from in-transit propagation effects.

The authors emphasize that the improvement in $H_0$ precision is indirect, mediated by the activation of the southern sky and the tightening of the slope $\beta$ through the addition of new anchors. Furthermore, the work posits that if high-redshift neutrino sources can be identified and standardized, neutrinos could provide a novel, independent window on cosmological parameters $\Omega_m$ and $w$ , complementing existing constraints from supernovae and the CMB.

The authors note that realizing these projections requires close coordination between the neutrino and X-ray communities to improve flux measurements of anchor galaxies and refine absorption modeling, particularly for Compton-thick sources. They also acknowledge that the discovery of new Seyfert sources, particularly in the Southern sky, could further enhance future measurements.

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