ASTRONOMY COLLOQUIUM

Radio astronomy at centimeter to meter wavelengths has experienced a technological revolution in the past decade, enabling transformational combinations of sensitivity, field of view, and time resolution. The recent discoveries are headlined by fast radio bursts (FRBs): energetic (>10^39 erg), millisecond-duration impulses observed across the Universe. Although FRBs are likely associated with neutron stars, they appear to occur in a remarkable diversity of environments. Understanding the formation of FRB sources is thus intertwined with problems in neutron-star formation. Regardless of their origins, FRBs form exquisite tracers of the contents and physical conditions of the otherwise "missing" baryons along their sightlines. At Caltech, we have built the Deep Synoptic Array (DSA-110) radio telescope, which is discovering and pinpointing FRBs to host galaxies at a world-leading rate. The results from our program shed new and arguably conclusive light on the origins of FRBs. Further, DSA-110 discoveries have, for the first time, sensitively determined the split between the cosmic baryon contents around and in between galaxies. Our results favor scenarios where moderately strong feedback from galaxy formation processes evacuate galaxy halos, and pave the way for the role of FRBs in precision cosmology.