Stacked JWST images give little red dots compact host galaxies
A study stacking 217 JWST little red dots found faint host-galaxy light. Another used Planck anisotropies to limit slow dark-sector transitions to less than 1 per cent of dark energy.
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A JWST stack reveals faint light around little red dots
The team publishing in Nature Astronomy stacked JWST images of 217 little red dots from the COSMOS-Web survey in four near-infrared bands. Optical emission too faint to see around most individual objects extended beyond the central point source in the combined image. The average object sits inside a star-forming galaxy of about 1 billion solar masses with a radius near 210 parsecs. That size corresponds to a structure about 2.5 times more compact than star-forming galaxies of similar mass at the same epoch.[1]
The stacked image describes the sample average
The extended emission cannot be resolved around most little red dots individually, so the study describes the average of the sample rather than a particular object. The authors interpret the result as supermassive black holes sitting at the centres of compact star-forming galaxies. That remains a proposed interpretation. Spectroscopic observations are still needed to confirm the distances assumed in the stacking. The report therefore preserves the boundary between the host component visible in the combined JWST image and a claim that the same component applies to every little red dot.[1]
Planck puts a 1 per cent ceiling on slow dark-sector transitions
A theoretical analysis in Physical Review Letters calculated what a first-order phase transition in a hidden dark sector during the late era of dark-energy domination would leave in the cosmic microwave background. Using directional variations in Planck photons, the team limited the vacuum energy released by completed transitions with a rate parameter of 25 or less to below 1 per cent of dark energy. The constraint comes from anisotropy rather than the average expansion rate. With a rate parameter of 500 or less, the calculation leaves at least 14 billion years before a possible turn from expansion to contraction could produce a cosmic collapse.[2]
