My research focuses on supernova (SN) explosions and gravitational lensing by galaxies and galaxy clusters. Supernovae (SNe) offer the opportunity to study the deaths of individual stars far beyond the local universe, and thermonuclear SNe Ia are excellent tools for measuring the expansion history of the universe. Recent work includes the discovery of an individual, luminous blue supergiant star at redshift z=1.5 (a look-back time of 9.3 billion years) which is highly magnified (~2000 at peak) by a foreground galaxy cluster. The star's microlensing flux variations offer a new window into the nature of galaxy-cluster dark matter, the initial mass function, and the evolution of massive stars. The blue supergiant star was found in the same lensed galaxy where the first-known multiply imaged, strongly lensed SN (dubbed SN Refsdal) appeared in late 2014 in an Einstein cross configuration. The timing of a subsequent reappearance of the SN, at an offset of ~8 arcseconds from its original location, in 2015 disagrees with most but not all predictions, and illustrates a promising approach for identifying the most accurate cluster-modeling techniques and magnification maps.
Assistant Professor, School of Physics and Astronomy and Minnesota Institute for Astrophysics