Original title: TDCOSMO XXIX: JWST/NIRSpec IFU Spatially Resolved Kinematics of Three Time-delay Lenses
Shawn Knabel, Pritom Mozumdar, Anowar J. Shajib, Tommaso Treu +7 · September 2026
Astronomers want to measure the Hubble constantA number that describes the rate at which the universe is expanding., which describes how fast our universe expands. A massive galaxy can act like a lens, bending light from a distant quasar into multiple images. Flashes of light arrive at different times along these paths. However, an issue called the mass-sheet degeneracyA mathematical ambiguity in gravitational lensing where different mass distributions can produce similar observational effects. makes it hard to measure the deflector galaxy's mass profile accurately. To solve this, researchers used the James Webb Space Telescope's Near-Infrared Spectrograph to track how stars move inside deflector galaxies across three quadruply lensed quasar systems. Tracking stellar motions reveals where mass actually sits inside the deflector galaxy, which breaks that mathematical ambiguity. The team produced detailed motion maps, categorized one galaxy as a fast rotator and two as slow rotators, and refined source redshifts. These precise measurements will soon help calculate better cosmological parameters.
Imagine you are trying to guess the weight of a large crowd by watching how it flows through a park. If you only measure the crowd at one spot, it might seem lighter or heavier depending on where people cluster. Here, astronomers are mapping how stars move throughout entire galaxies to accurately determine their mass, which is crucial for calculating how fast the universe is expanding.
This work improves the precision of measuring the Hubble constant, which tells us how fast the universe is expanding. More accurate measurements help resolve discrepancies in cosmological models and deepen our understanding of the universe's age and structure.
The abstract does not explicitly state limitations, but it indicates that cosmological parameters will be measured in an upcoming publication, so this study alone does not provide those final constraints. It also only covers three specific lens systems, and the improvements are in data reduction and methodology for these cases.
Ask anything about this paper. Answers come from its abstract, and say so when the abstract doesn't cover your question.
TDCOSMO XXIX: JWST/NIRSpec IFU Spatially Resolved Kinematics of Three Time-delay Lenses — Shawn Knabel, Pritom Mozumdar, Anowar J. Shajib et al.
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.