Event ID: INT-25-2b

Note to applicants: This is a "hybrid" program, meaning there will be a combination of virtual and in-person participants. In the COMMENTS section of the Application Form, please write [In-person], [Virtual], or [Either] to reflect your preferred mode of attendance. 

OVERVIEW

Neutron star mergers are unique laboratories of extreme astrophysics. These powerful phenomena hold the key to long-standing questions, ranging from the origin of observed short gamma-ray bursts (associated with energetic jets launched following magnetic-field enhancement likely following the formation of a black hole surrounded by a matter disk) to kilonovae and the origin or heavy elements (associated with low-density matter outflows and rapid nucleosynthesis reactions) and the equation of state for hot and dense matter (encoded in the gravitational-wave signal from the merger dynamics).

A particularly exciting aspect of the spectacular GW170817 event, from the nuclear physics perspective, was the subsequent observation of kilonova emission in the optical and the infrared, a transient signal powered by the radioactive decay of heavy nuclei produced in rapid neutron capture (r-process) nucleosynthesis. This was the first convincing evidence of cosmic r-process production. It may even suggest that most heavy elements in the Universe originate in mergers. However, many questions remain and progress in nuclear physics is key to finding the answers. With the first results coming out of the Facility for Rare Isotope Beams (FRIB) the potential to narrow down uncertain nuclear parameters with collider experiments is evident. This will help focus the nuclear network calculations required to estimate the exotic nuclei produced in mergers, the associated radioactivity and the electromagnetic emission. In addition, improved results for nuclear masses will constrain the key parameters for the equation of state of matter under the extreme conditions present in a neutron star core. This, in turn, helps narrow down the parameter space that needs be considered in simulations that aim to support future gravitational-wave searches and parameter inference.

The fundamental questions associated with the astrophysics effort are closely related to current and future developments in nuclear physics, both on the theory side and for collider experiments. With this broad scope in mind, this three-week program, closely linked to a workshop focused on beyond equation of state aspects [link], aims to bring together experts from across the range of relevant disciplines – from theory to simulations and observations - to engage with the challenges we face as high precision experiments and more sensitive observations become available in the next decade.

TOPICS AND FORMAT

The program is based on 3 themed weeks of discussion which should attract interest from a broad community.  Briefly, the science topics covered by the three weeks are:

Week 1 (September 2-5): Equation of state for hot and dense matter

The first week of the program will focus on issues related to the equation of state of extreme density matter. We aim to reach a consensus view of the main issues that need to be accounted for to understand results from collider experiments and the outcome of neutron star mergers, e.g. in the context of the r-process operating in low-density matter outflows. Time will be dedicated to exploring common aspects of astrophysical observations and nuclear physics experiments, like insights into nucleosynthesis gleaned from results from FRIB.

Workshop (September 8-12): Nuclear Physics in Mergers - Going Beyond the Equation of State

The separate workshop 25-94W, “Nuclear Physics in Mergers - Going Beyond the Equation of State”, organized by A. Haber, E. Most, and C. Raithel, will take place between weeks 1 and 2 of our program. If you wish to attend the workshop week, you must apply to the workshop separately.

Week 2 (September 15-19): Simulating neutron star mergers

The second week of the program brings together experts in state of the art numerical simulations. We will discuss the range of physics required for robust numerical models,  including finite temperature effects, neutrino aspects and issues related to transport phenomena. The aim is to explore issues that need to be resolved in order for simulations to reach the precision required for future gravitational-wave constraints on the equation of state for hot and dense matter.

Week 3 (September 22-26): Multi-messenger astronomy

The final week of the program aims to establish a holistic view of the promises of multi-messenger astronomy in the next decade. Key problems include information that can be gleaned from high-precision gravitational-wave measurements with next-generation instruments, the origin of short gamma-ray bursts and possible constraints on nuclear physics (like the threshold mass for gravitational collapse) one may obtain from observations. We will also focus attention on the optical/infrared signals associated kilonovae and what observations may tell us about nucleosynthesis and the formation of heavy elements. The interdisciplinary overlap with upcoming nuclear experiments will be central to the discussion.