Stellar Cartography

Envisioning The Distance Ladder In The Era Of The Habitable Worlds Observatory

By Keith Cowing

Status Report

astro-ph.CO

July 5, 2025

Filed under astro-ph.CO, astronomy, exoplanet, Habitable Worlds Observatory, Habitable Zone, imaging, Stellar Cartography, telescope

Envisioning The Distance Ladder In The Era Of The Habitable Worlds Observatory — A comparison of state-of-the-art geometric distances that serve to anchor the distance scale and their current relative uncertainties. Additional candidate (≲1 Mpc) eclipsing binary hosts to target in future are also pictured. Current EB distances to M31 and M33 rely on early-type stars and are not precise enough to be included in H0 determination (Vilardell et al. 2010; Bonanos et al. 2006), but we expect this will improve with more sensitive moderate- to high-resolution spectroscopy capable of characterizing late-type EB systems. — astro-ph.CO

The current state-of-the-art cosmic distance ladder requires three rungs–geometric distances, primary indicators, and Type Ia Supernovae–to achieve a 1% measurement of the Hubble constant H0.

The Habitable Worlds Observatory will have the sensitivity and resolution to reduce this to a two-step measurement, eliminating the third rung entirely and reaching into the Hubble flow with stellar distance indicators such as Cepheid variables and the tip of the red giant branch alone.

We discuss the requirements for a program to measure H0 to 1% with HWO here, including telescope and instrument design considerations. We also comment on the potential of HWO to measure distances to low-mass dwarf galaxies via their RR Lyrae stars.

Gagandeep Anand, Meredith Durbin, Rachael Beaton, Joseph Jensen, Adam Riess

Comments: Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology SCDD, to be presented at HWO2025 and submitted to Astronomical Society of the Pacific following community comments. Feedback welcomed
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2507.02056 [astro-ph.CO] (or arXiv:2507.02056v1 [astro-ph.CO] for this version)
https://doi.org/10.48550/arXiv.2507.02056
Focus to learn more
Submission history
From: Meredith Durbin
[v1] Wed, 2 Jul 2025 18:00:32 UTC (8,789 KB)
https://arxiv.org/abs/2507.02056
Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

Follow on Twitter