James Webb Space Telescope Feed Post
JWST's PEARLS: Mothra, a new kaiju star at z=2.091 extremely magnified by MACS0416, and implications for dark matter models
Stacked difference Pi=3 i=1 (F200W - ai × FnnnWi), where ai was chosen to minimize the contribution from the arc to the difference, and FnnnWi are all filters with wavelengths below 2 µm, that is F090W, F115W, and F150W. These were degraded to the resolution of F200W using the star-derived PSF in Appendix B. The individual differences are shown in column 3 of Figure B.2. The stacked image has been smoothed with a Gaussian of FWHM = 0 '' .09 to increase the contrast. The position of LS1 is marked with a white arrow. The position of the possible counterimage LS1' , ˜0 '' .1 from LS1, is marked with a yellow circle.
Abstract: We report the discovery of Mothra, an extremely magnified monster star, likely a binary system of two supergiant stars, in one of the strongly lensed galaxies behind the galaxy cluster MACS0416. The star is in a galaxy with spectroscopic redshift z=2.091 in a portion of the galaxy that is parsecs away from the cluster caustic. The binary star is observed only on the side of the critical curve with negative parity but has been detectable for at least eight years, implying the presence of a small lensing perturber. Microlenses alone cannot explain the earlier observations of this object made with the Hubble Space Telescope. A larger perturber with a mass of at least 104\,\Msun\ offers a more satisfactory explanation. Based on the lack of perturbation on other nearby sources in the same arc, the maximum mass of the perturber is M<2.5×106\,\Msun, making it the smallest substructure constrained by lensing above redshift 0.3. The existence of this millilens is fully consistent with the expectations from the standard cold dark matter model. On the other hand, the existence of such 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 are excluded by our observations. Similarly, axion dark matter models are consistent with the observations only if the axion mass is in the range 0.5×10-22eV
