Comparison of a Model of a Blue Supergiant’s Spectrum with Observational Data

Scientists found that the Hubble data from MACS J1149+2223 Lensed Star 1 (Icarus) matches the model for a blue supergiant. The agreement shows a remarkably good fit, and indicates that Icarus is approximately twice as hot as the Sun. The solid blue line shows the model spectrum of the blue supergiant, adjusted for the distance to the host galaxy of the highly magnified star. The red diamonds are the actual data measured for Icarus. The observed wavelength of the Balmer discontinuity relative to its intrinsic wavelength (at about 365 nm) is an indicator of the distance to the star. The strength of the Balmer discontinuity depends on the strength of the star’s gravity at its surface and its temperature.