The Supermassive Podcast · The Royal Astronomical Society

BONUS - Overmassive Galaxies

·23 min·2 clips

JWST's latest data deepens the mystery of the universe's expansion rate, challenging our understanding of dark energy.

Science journalist Izzy Clark hosts astrophysicist Dr. Becky Smedhurst and Royal Astronomical Society deputy director Dr. Robert Massey for a two-year JWST retrospective. The Hubble tension is the first major topic: JWST measured Cepheid variable stars 130 million light years away and still found the discrepancy between the two methods of measuring the universe's expansion rate, though a competing group presenting at conferences claims JWST has resolved the tension. No definitive paper has been published yet, leaving cosmologists frustrated and impatient. The Horsehead Nebula receives extended discussion, with Massey describing JWST's close-up of an 0.8-light-year section revealing dust and soot structure in infrared, and comparing it with Hubble's and Euclid's different-field-of-view images of the same target. Smedhurst focuses on two areas where JWST has had outsized impact: the most distant universe and exoplanet atmospheres. On the distant universe side, JWST recently found a candidate for the most distant supermassive black hole, raising questions about how quickly black holes could grow in the early universe. The "overmassive galaxies" finding is given extended treatment: JWST found early universe galaxies far more massive than models predict, prompting debate about whether the initial mass function (the distribution of stellar masses at formation) differs in the early universe. Smedhurst explains that if early stars were skewed toward higher masses, the inferred galaxy masses drop back into alignment with models. The TRAPPIST system planets are discussed as disappointing so far, with TRAPPIST-1b and 1c appearing to be bare rock with no atmospheres detectable by JWST. The hosts recommend space-adjacent books, films, and exhibitions in lieu of a traditional book club, acknowledging time constraints.

As heard by us

JWST gets a grounded check-in, from galaxy headlines to exoplanets and the Hubble tension.

The episode starts with a look at what JWST has done since the first images, then settles into the larger shift it is forcing on the story rather than the headlines.

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Why you'd press play

Press play for a JWST check-in that cuts through the galaxy hype.

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