My research focuses on the intersection of astrophysics and nuclear physics, specifically in core-collapse supernovae and compact object mergers. When a massive star runs out of nuclear fuel to burn in its core, its inner most regions can rapidly collapse and form a hot, dense neutron star that emits a prodigious number of neutrinos. These neutrinos deposit a fraction of there energy further out in the star and likely power a large fraction of the supernovae observed in nature. Additionally, the emitted neutrinos can have a significant impact on the nuclei that are produced during the supernova and the neutrinos from nearby supernovae can be directly detected.
In compact object mergers, two neutron stars or a neutron star and a black hole in a binary system emit gravitational radiation and spiral in towards each other. When they merge, a hyper massive hot neutron star or a black hole is left behind along with an accretion disk and a significant amount of very neutron rich material is ejected. These events are a strong source of gravitational waves, they may power short gamma ray bursts, and they may be the source of the heavy r-process nuclei found in our galaxy.
Looking ahead, the physics of compact objects in dynamic scenarios will be an area of cutting edge research in astronomy and nuclear astrophysics. Modern experimental facilities, such as the FRIB, will provide significant constraints on the microscopic properties of these environments. A wealth of new information about these events will be available in a few years from next generation gravitational wave detectors like advanced LIGO and large scale optical transient surveys like LSST. It is also possible that the neutrino signal from a galactic supernova will be observed with modern neutrino detectors in the relatively near future, opening a direct window into the innermost regions of supernovae and the birth of neutron stars. Detailed understanding of what these multi-messenger observations are telling us requires precise modeling of both microphysical processes (i.e. the nuclear equation of state, neutrino opacities, and nuclear burning) and macrophysical processes (i.e. radiation hydrodynamics and general relativity) in exotic environments
I approach these problems using both theory and computation. Recently, I have worked on characterizing the composition of the material ejected during binary neutron star mergers, on how strong interactions in dense matter affect neutrino opacities and thereby the properties of neutrinos emitted in supernovae, methods for radiation transport in supernovae, and models of the core collapse supernova explosion mechanism. I am still actively working on projects in all of these areas.
L. F. Roberts, et al., General Relativistic Three-Dimensional Multi-Group Neutrino Radiation-Hydrodynamics Simulations of Core-Collapse Supernovae, submitted to ApJ, [arXiv:1604.07848] (2016).
J. Lippuner & L. F. Roberts, r-process Lanthanide Production and Heating Rates in Kilonovae, ApJ 815, 82 (2015).
L. F. Roberts, S. Reddy, and G. Shen, Medium Modification of the Charged Current Neutrino Opacity and Its Implications, Phys. Rev. C 86, 6 (2012).
L. F. Roberts, G. Shen, V. Cirigliano, J. A. Pons, S. Reddy, and S. E. Woosley, Proto-Neutron Star Cooling with Convection: The Effect of the Symmetry Energy, Phys. Rev. Lett. 108, 061103 (2012).
L. F. Roberts, S. E. Woosley, and R. D. Hoffman, Integrated Nucleosynthesis in Neutrino-driven Winds, ApJ 722, 1 (2010).