UNIVERSITY PARK, Pa. — A pair of new grants from the U.S. National Science Foundation (NSF) and the German Research Foundation (DFG) will support an international research collaboration and student exchange program between Penn State and the University of Jena in Germany. The grants will support research to produce a database of simulations of neutron stars merging with other neutron stars or black holes. This work will not only explore the physics of incredibly energetic cosmic events but also lend insight into how rare-earth elements and heavy metals are formed and provide a frame of reference to interpret future observations of merger emissions.
The $392,000 NSF grant is awarded to David Radice, Knerr Early Career Professor of Physics and and associate professor of astronomy and astrophysics in the Eberly College of Science at Penn State, and the DFG grant is awarded to Radice’s colleagues in Germany.
The collision and merger of two neutron stars, or of a neutron star with a black hole, are some of the most energetic events in the universe. These events produce gravitational waves, or ripples in space time that can be detected on Earth with observatories like NSF’s Laser Interferometer Gravitational-Wave Observatory (LIGO). Mergers also often result in the ejection of matter into space, which produces electromagnetic radiation like gamma rays, X-rays, and visible light that can be detected with ground-based observatories like NSF’s Vera Rubin Observatory and space-based observatories like NASA’s James Webb Space Telescope.
“Gravitational waves and electromagnetic radiation resulting from neutron star mergers are typically modeled separately,” Radice said. “Our research team plans to model them together so that we have the theoretical framework necessary to interpret future observations and better understand the physics behind these explosive events.”
According to Radice, neutron star mergers act as a sort of cosmic laboratory, allowing researchers to study extreme physics in situations that cannot be safely tested on Earth. They can also help answer ongoing questions about the origin of rare-Earth elements and metals like gold in the universe, which can be created during these mergers. Rare earth elements are metals that are important for making modern technologies like smartphones, magnets and batteries.
The research team will build computer models that capture the physics of mergers and simulates how neutron stars — and sometimes black holes — orbit each other as they grow closer and eventually merge as well as the resulting remnants and emissions. They will ultimately produce a database of about 1,000 simulations, exploring a variety of merger conditions such as the mases of the colliding objects and whether they are predominantly composed of traditional particles like protons and neutrons or more exotic particles like quarks. The researchers will also produce a tool that scientists can use to interpret future observations and to predict, for example, how much matter is ejected with different masses and properties of the merging objects.
“Writing the software to make these simulations takes a lot of effort, and it's beyond the expertise of any single group, so we collaborate with other research groups that bring their own expertise,” Radice said. “The German group contributes a lot of knowledge and code around the general relativity that goes into waveform modeling, whereas we contribute our expertise and code in multiphysics, or complex interactions of physical forces, like hydrodynamics. We have really complimentary expertise, and we are looking forward to sharing that expertise with undergraduate students.”
The grants will also allow an undergraduate student from Penn State to conduct research in at the University of Jena, and for an undergraduate student from University of Jena to study at Penn State, for 10 weeks during the summer.
“This is a great opportunity for students from both universities to experience different research environments and lifestyles,” Radice said. “Both research groups are conducting state-of-the-art research, and we are excited to start this project.”
Undergraduates interested in participating in this project should contact Radice via email.