One of today’s greatest cosmic puzzles concerns the expanding Universe.
Two major methods each give low-error, but incompatible, answers.
By tracking an early, relic signal’s evolution, we measure expansion of 67 km/s/Mpc.
By starting nearby and observing increasing recession with distance, we measure 73 km/s/Mpc.
This discrepancy — the “Hubble tension” — is a modern cosmic conundrum.
Many speculate an observational error on the “distance ladder” side could be the culprit.
We start by observing Cepheid variable stars within the Milky Way.
We accurately infer their distances by measuring astronomical parallax.
Then we measure Cepheids in nearby, well-measured galaxies.
Finally, we measure type Ia supernovae within those galaxies and beyond, linking these cosmic “rungs” together.
Could an error in Cepheids be biasing our measured expansion rate?
By measuring Cepheids in nearby galaxies, JWST probes this possibility.
Observing galaxy NGC 4258, JWST found no photometric bias for Cepheids.
Instead, it confirmed and enhanced previous Hubble Space Telescope findings.
Cepheids in NGC 5584, which also had a (2007-era) type Ia supernova, also reveal no bias.
The period-luminosity relation, a key calibrator of Cepheids, is now more precise than ever.
With superior resolution, JWST has reduced any uncertainties down to their smallest values ever.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.