Direct detection of the first stars

The first generation of stars – the metal-free Population III – played an important role in the early Universe by ending the cosmic dark ages, by producing the first elements beyond hydrogen, helium and lithium, and possibly by seeding the Universe with black holes that grew into the first quasars.

These stars are predicted to be predominantly more massive than stars that form in later stellar generations, but no such stars have yet been found.

A new method, based on extreme magnifications due to gravitational lensing by foreground galaxy clusters, now makes it possible to directly detect Population III stars in the early Universe, and the first very massive, lensed star was recently discovered at redshift z=6, i.e., in an epoch about one billion year after the Big Bang.

Observing time on the James Webb Space Telescope (JWST) has now been secured by our team to further characterize this object and to carry out a survey for other lensed stars in the high-redshift Universe.

In this project, we will 1) develop the first models for the photometric and spectroscopic properties of lensed stars in the high redshift Universe, 2) analyze the lensed star candidates detected in the first four years of JWST operations and 3) from these data set the first JWST-based observational constraints on the cosmic star formation rate and on the stellar initial mass function of Population III stars in the early Universe.