A Hundred and Nine Flashes
About this episode
This episode discusses the use of 109 fast radio bursts to measure galactic feedback and its effects on matter in the universe.
Today's episode — S05E190, Thursday September 10, 2026: Main story: 109 fast radio bursts have been used to measure how much galactic feedback has smoothed out the matter in the universe. A fast radio burst lasts about a millisecond, and on its way to us it is dispersed — low radio frequencies slowed more than high ones by free electrons along the path, exactly the way a prism separates white light. The size of that delay counts the ordinary matter the burst passed through. Writing in Nature Astronomy on 8 September, a team led by Kritti Sharma at Caltech, with Vikram Ravi, Liam Connor and Elisabeth Krause (University of Arizona), used 109 bursts localised to host galaxies out to redshift ~0.3 — most of them from Caltech's DSA-110 — to constrain the suppression of matter clustering by feedback, and the gas fractions of groups and clusters between 10^13 and 10^15 solar masses. They find more gas retained than the X-ray picture implies: gas fractions about 1.9σ above stacked eROSITA measurements, and slightly above the Atacama Cosmology Telescope's kSZ constraints, consistent with the bursts counting cool gas that X-rays miss. The constraint is already competitive with both of…
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