Vol. 672
3. Cosmology

JWST’s PEARLS: A new lens model for ACT-CL J0102-4915, “El Gordo,” and the first red supergiant star at cosmological distances discovered by JWST

by J. M. Diego, A. K. Meena, N. J. Adams, et al. 2023, A&A, 672, A3

This paper presents new strong-lensing mass modeling of the high-z (z=0.87) El Gordo massive cluster using recently obtained JWST imaging data. In addition, it introduces new candidates for caustic-crossing events that demonstrate the power of the JWST.

The number of lenses is enhanced by the presence of an overdensity of background galaxies (at a redshift of z=4.3). The large number of new multiple image candidates revealed by the JWST data helps improve the mass modeling of this cluster. This cluster is known for its high mass, which is difficult to explain in the framework of Lambda cold dark matter cosmology so early in cosmic time.

The most likely explanation for one of the caustic-crossing events is a red supergiant star that the authors nicknamed "Quyllur," the Quechua term for star. If confirmed at the proposed redshift of z=2.18, this would be the first red supergiant found at cosmological distances.