NBIA Astroparticle Seminar: Ylva Götberg

A third of all massive stars should lose their hydrogen-rich envelopes by interaction with a binary companion, leaving the hot and compact helium core exposed. These "stripped stars" are thought to emit copious amounts of ionizing radiation, and to be the main progenitors of both stripped-envelope supernovae and neutron stars that merge in a gravitational wave event. However, despite their importance, stripped stars had remained elusive. Building upon my theoretical predictions, we initiated an observational search for the missing population of stripped stars. Through excess ultraviolet radiation, we could identify hundreds of candidates in the Magellanic Clouds. In an extensive follow-up program, we observed the optical spectra for a subset and thus confirmed their stripped nature. This discovery of a new type of star unlocks the opportunity to explore many new scientific directions that previously have been unaccessible. In addition to providing urgently-needed benchmarks for binary evolution and population synthesis codes, they also allow for studying the deep interiors of evolved massive stars and the origin of hard ionizing emission.