College of Science & Engineering
Twin Cities
Hubble Space Telescope and James Webb Space Telescope observations of nearby galaxies resolve those galaxies into individual stars. A fraction of those stars show variability on the time scales of the length of the observations. The RR Lyrae variable stars are of particular interest. With periods of about 12 hours, their light curves can be extracted from the deep observations of nearby galaxies, which require long integrations. The RR Lyrae stars provide a very well calibrated method to determine distances to galaxies, making them particularly useful. They also arise from a low mass range such that their variable stage means that they must be at least 10 Gyr old. This property enables them to be used to trace the star formation rate near at the earliest ages of the universe. Identifying, extracting, and characterizing these stars is computationally intensive and these researchers are involved in a large archival project to put all of the Hubble Space Telescope observations of variable stars in nearby galaxies into a uniform and homogeneous study. They are also studying some the first James Webb Space Telescope observations of nearby galaxies.