H0 Tension on the Light of Supermassive Black Hole Shadows Data - Forecasting and Breaking Parameter Degeneracy

Aug 29, 2026

Cosmological tensions motivating new probes focus on determining the Hubble constant H0 through independent techniques, contrasting the distance-ladder calibration approach with model-dependent inferences from the angular size of the sound horizon. The work extends studies of recently detected supermassive black hole shadows as standard rulers, characterized by the shadow’s angular size and black hole mass. By forecasting and fixing conditions at higher redshifts, parameter degeneracy is reduced, enabling ~4% precision and improved estimates of H0 and baryonic mass density, supporting SMBH shadow physics as a path to address tension issues.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages12

Reading Time30 min

AccessFree to download

Introduction

Hubble constant tension and measurement approaches

Motivation for new observables

Black hole shadows as standard rulers

arXiv :2301 .00490v1 [ astro-ph .CO] 2 Jan 2023 H0 Tension on the Light of Supermassive Black Hole Shadows Data Celia Escamilla-Rivera 1, a and Rub􀀓en Torres Castillejos2, b 1 Instituto de Ciencias Nucleares, Universidad Nacional Aut􀀓onoma de M􀀓exico, Circuito Exterior C. U. , A. P. 70-543, M􀀓exico D. F. 04510, M􀀓exico 2 Facultad de Ciencias en F􀀓􀀐sica y Matem􀀓aticas, Universidad Aut􀀓onoma de Chiapas, Calz. Emiliano Zapata Km. 8, Tuxtla Guti􀀓errez 29050, Chiapas, Mexico. Cosmological tensions in current times have opened a wide door to study new probes to constrain cosmological parameters, speci􀀌cally, to determine the value of the Hubble constant H0 through independent techniques. The two standard methods to measure/infer H0 rely on: (i) anchored observables for the distance ladder, and (ii) establishing the relationship of the H0 to the angular size of the sound horizon in the recombination era assuming a standard Cosmological Constant Cold Dark Matter (􀀃CDM) cosmology. However, the former requires a calibration with observables at nearby distances, while the latter is not a direct measurement and is model-dependent. The physics behind these aspects restrains our possibilities in selecting a calibration method that can help minimise the systematic e􀀋ects or in considering a 􀀌xed cosmological model background. Anticipating the possibility of deeply exploring the physics of new nearby observables such as the recently detected black hole shadows, in this paper we propose standard rules to extend the studies related to these observables. Supermassive black hole shadows can be characterised by two parameters: the angular size of the shadow and the black hole mass. We found that it is possible to break the degeneracy between these parameters by forecasting and 􀀌xing certain conditions at high(er) redshifts, i.e. , instead of considering the 􀀙10% precision from the EHT array, our results reach a 􀀙 4%, a precision that could be achievable in experiments in the near future. Furthermore, we found that our estimations provide a value of H0 = 72:89 􀀆 0:12 km/s/Mpc and, for the baryonic mass density,􀀊 m = 0:275 􀀆 0:002, showing an improvement in the values reported so far in the literature. We anticipate that our results can be a starting point for more serious treatments of the physics behind the SMBH shadow data as cosmological probes to relax tension issues. 1. INTRODUCTION One of the most challenging problems of modern cosmology is the statistical tension on the estimation of the expansion rate of the universe today: the Hubble constant H0 . Di􀀋erent experiments, observables and predicted theoretical models gives H0 values that disagree strongly. Therefore, in order to determine H0 , the distance to observables on astrophysical and cosmological scales is one of the most relevant factors since measurements of this constant in the local universe based on distance ladder methods do not match the estimated value in the early universe, where the 􀀌rst methodology takes into account serious statistical precision analysis and the latter considers a standard cosmological model supported by observational evidence. The most pressing issue, in particular for this tension, is the 5.0􀀛 disagreement between the local value given by the SH0ES collaboration [1] (H0 = 73.04 􀀆 1.04 km/s/Mpc) and the early estimated value given by the Planck collaboration [2] (H0 = 67.27 􀀆 0.60 km/s/Mpc) . While measurements involved in each sector of the early and late universe agree, e.g. , CMB and BAO observations, 1 the H0 tension persists at the ends of the empirical distance ladder. Several proposals have been raised to 􀀌nd a viable solution to this issue. On one hand, it is possible to consider late H0 measurements which do not require a benchmark model, such as the standard Cosmological Constant Cold Dark Matter (􀀃CDM) model. On the other hand, early H0 measurements can be performed if we assume a collection of physical properties based on a

FAQs

What is the main goal of the paper regarding the Hubble constant H0?

To constrain H0 using supermassive black hole shadow observables as independent cosmological probes, addressing the tension between early- and late-universe estimates.

How are supermassive black hole shadows used in this work?

They are treated as standard rulers whose angular shadow size and black hole mass can be related through an angular size–redshift framework.

What method helps break the degeneracy between shadow parameters?

The paper forecasts and fixes certain conditions at higher redshifts, improving achievable precision compared with the baseline EHT-level precision.

Aug 29, 2026

Uploaded by Riley West