James Webb Space Telescope Feed Post

Astronomy & Astrophysics highlight: JWST's PEARLS: Mothra, a new kaiju star at z=2.091 extremely magnified by MACS0416, and implications for dark matter models

by J.M. Diego, Bangzheng Sun, Haojing Yan, et al. 2023, A&A, 679, A31 Thanks to gravitational amplification, it is now possible to detect individual stars at very large distances in galaxies inhabiting the early Universe, 10 billion years ago. This is the case of Mothra, an extremely magnified monster star, likely a binary system of two supergiant stars, that has been discovered in one of the strongly lensed galaxies behind the galaxy cluster MACS J0416.1-2403. Mothra is located in a galaxy at redshift z = 2.091, very close to the cluster caustic, which explains part of its huge amplification. The binary star has been detectable for at least 80 years with the Hubble Space Telescope, which indicates there is a small lensing perturber as well. The mass of the perturber is believed to be between 10 000 and 2.5 million solar masses. The existence of this “millilens” is fully consistent with expectations from standard cold dark matter cosmology. The existence of such a small substructure in a cluster environment has implications for other dark matter models. In particular, warm dark matter models with particle masses below 8.7 keV ***can be ruled out, and the mass of a possible axion should lie in the range 0.5 to 5 10-22 eV.