Abstract
Gravitational lensing enables the detection of individual highly-magnified stars at cosmological distances – referred to as lensed star transients, as these stars are only temporarily magnified above the detection threshold. Over the last decade, hundreds of such events have been discovered in observations with the Hubble and James Webb Space Telescopes towards galaxy clusters.
In this seminar, I shall show that we have pioneered the use of these events to address three outstanding problems in astrophysics: (1) the spatial distribution of lensed stars is used to map the underlying dark matter substructure, finding that predictions made assuming ultra-light axions better reproduce the observations than weakly interacting massive particles; (2) the lensed star detection rate serve as an independent probe of the stellar initial mass function at distant galaxies, showing evidence of the universality of initial mass function until redshift ~1; (3) the relative detection rate of lensed stars at channels that are most sensitive to blue and red supergiants allow us to probe the most recent star formation history, revealing a missing episode of star burst that would have been missed without using lensed stars as constraints.
Last but not least, I shall discuss the possibility of observing lensed stars not only in galaxy clusters, but also in cases where individual galaxies act as gravitational lenses.
Anyone interested is welcome to attend.