Astrophysical observations of the cosmos allow us to probe extreme physics and answer foundational questions on our universe.  Modern astronomy is increasingly operating under a holistic approach, probing the same question with multiple diagnostics including how sources vary over time, how they appear across the electromagnetic spectrum, and through their other signatures, including gravitational waves, neutrinos, cosmic rays, and dust on Earth. Astrophysical observations are now reaching the point where approximate physics models are insufficient. Key sources of interest are explosive transients, whose understanding requires multidisciplinary studies at the intersection of Astrophysics, Gravitational Physics, Nuclear Science, Plasma Physics, Fluid Dynamics, Computational Physics, Particle Physics, and Atomic, Molecular, and Optical Science, and their corresponding interdisciplinary fields. Many of these fields are seeking to broaden the impacts of their results, or to move towards more complete understanding of a question by studying it over multiple scales, including extremes only reached in astrophysical environments. Incorporating fundamental physics into higher fidelity astrophysical observables requires both high-performance computing studies and enhanced data analysis methodologies. Multidisciplinary studies must occur across the separate physics disciplines, but also across bifurcation in professional societies, general meetings, funding agencies, advisory committees, and Decadal reviews (and other long range planning documents). Even within astrophysics itself, greater integration of theory and data analysis is required for progress.

To foster multidisciplinary research in the area of explosive transients, Louisiana State University, the DOE’s Los Alamos National Lab and Center for Nuclear Astrophysics Across Messengers, NASA’s Physics of the Cosmos Program, and the National Science Foundation, invite the international community to participate in a workshop in Baton Rouge, LA during September 23-26, 2024. The workshop goals are to identify opportunities in multidisciplinary studies, both in using information from other fields to interpret astrophysical observations, but also to use astrophysical observations to probe outstanding questions in other fields. We invite the community to review the current state of resources in the relevant fields, reporting on existing collaborations and partnerships which cross disciplines, and identify barriers to multidisciplinary research. This workshop aims to understand how the scientific return of facilities can be maximized through alignment of existing initiatives, facilities, and mechanisms and, if necessary, suggest the creation of new ones. Lastly, we ask the participants to conceive of methods to sustain growth in this area.

Guiding Questions

• Beginning with the questions outlined in the first time-domain and multimessenger white paper, what are the most important multidisciplinary questions of interest for time-domain and multimessenger astrophysics?

• What are the key measurements? How can we leverage current and forthcoming facilities? Do we need new ones? For astrophysical observations, are additional coordination recommendations needed beyond those in the second time-domain and multimessenger white paper?

• What advances are relevant for other fields of physics and national strategic priorities?

• How can multidisciplinary research be fostered? 

Workshop participants will contribute to a community-driven white paper which will be used to guide multidisciplinary science in this area. They will also identify focus areas for future meetings, including joint Division sessions at meetings of the American Physical Society. Outcomes may include programmatic input to funding agencies through existing mechanisms.

Rationale: 

The Astro2020 Decadal Report, Pathways to Discovery in Astronomy and Astrophysics for the 2020s, identified New Messengers, New Physics as one of three key themes this decade. The priority area in this theme is New Windows on the Dynamic Universe. Key questions include the equation of state of dark energy, the equation of state of neutron stars, the origin of the elements, tests of General Relativity, and seeking physics beyond the standard model. In response, NASA organized the first time-domain and multimessenger workshop in Fall of 2022, focused on the top science questions in this area. In Fall of 2023 the NSF, with NASA participation, organized the second time-domain and multimessenger workshop focused on the infrastructure to support coordination of the vast network of ground and space-based observatories in astrophysics. This will be the third meeting in these series, focusing on multidisciplinary studies of explosive transients, which are a priority in several disciplines. 

The 2023 Long Range Plan for Nuclear Science has nuclear astrophysics as one of four subfields, which is of relevance for all explosive transients, and proposes a density ladder analogous to the cosmological distance ladder. 2023 Particle Physics Project Prioritization Panel endorses new facilities for MeV and high energy neutrinos, as well as upgraded gravitational wave facilities. 2021 Plasma Science: Enabling Technology, Sustainability, Security, and Exploration emphasizes space as the final frontier for plasmas; it further highlights opportunities for inter-agency collaboration and highlights the necessity of improved understanding of explosive transients through advances in plasma research. 2020 Manipulating Quantum Systems : An Assessment of Atomic, Molecular, and Optical Physics in the United States recommends NASA and other agencies should increase investment in fundamental atomic, molecular, and optical science which is needed to address key questions in astrophysics. All of these planning documents emphasize the synergies between astrophysics and other research in their respective disciplines, as well as broader interests for industry and national strategic priorities.

The guiding questions above can be explored in the cases of specific explosive transients. Some are listed as examples below, but the workshop is inclusive of additional questions and sources.

• Thermonuclear (type Ia) supernovae are ‘standard candles’, objects whose observation allows determination of the distance from Earth. They are of key interest to the NSF and DOE Vera C. Rubin Observatory and NASA’s Nancy Grace Roman Space Telescope, whose observations will constrain the equation of state of dark energy. This will help us understand the evolution and fate of the universe and, hopefully, advance our understanding of what dark energy is. Once these new facilities are complete, the key outstanding limitation will be in the empirical calibration of their intrinsic brightness. Can we instead calibrate their brightness through physics? Can we determine their progenitors, and how they explode? This may be possible, but only through complex multidisciplinary studies and likely require new observational diagnostics, such as nuclear gamma-rays with NASA’s Compton Spectrometer and Imager, or a larger sample possible with larger-scale nuclear missions.

• Core-collapse supernovae were the first astrophysical multimessenger transient. Observations of SN 1987A through thermal neutrinos and nuclear gamma-rays set our current understanding of how they explode. A future Galactic event observed with forthcoming megaton-scale MeV neutrino detectors, including DOE’s Deep Underground Neutrino Experiment, would provide advances in neutrino physics. Observation of a nearby event by NASA’s Compton Spectrometer and Imager would provide precise understanding of the internal explosion. Such a study may be aided if future NSF gravitational wave interferometers also detect the core collapse. NASA’s Ultraviolet Explorer will observe the effect of the explosive shock as it interacts with the material surrounding the star. This multiphysics problem is of direct relevance to understanding radiation flow through stochastic media, of interest for national strategic priorities. All such studies would benefit from a mission designed to detect the initial shock breakout. These events can be further studied by the mass distribution of compact object binaries inferred by NSF’s Laser Interferometer Gravitational-Wave Observatory and NASA’s Laser Interferometer Space Antenna, as well as characterization of their remnants in the Milky Way. Probing nucleosynthesis in these events (and also others) requires handling of low-energy nuclear science, molecular dynamics, density functional theory, and detailed radiative transfer, which are probed by DOE and NSF facilities.

  • A prototype of a possible collaborative document of the multiphysics relevant for a given transient type is available here clfryer/MM-SNe: Living Image/Document for Multi-Messenger Diagnostics of the Engine Behind Core-Collapse Supernovae (github.com) for core-collapse supernovae.

• Novae occur when hydrogen from a large donor star accrete onto a white dwarf companion until a critical temperature is hit and a thermonuclear explosion occurs. The 2023 Long Range Plan for Nuclear Science suggests that the dominant nuclear reactions of interest for novae (i.e., through sodium) may be fully understood in the coming years. When paired with measurement of nuclear line intensity the isotopic abundances can be determined. One line may be detected with observations by ESA’s INTEGRAL spacecraft of the (80 year cycle) recurrent novae T Coronae Borealis, or by NASA’s Compton Spectrometer and Imager in the coming years. As emphasized in the first TDAMM Workshop white paper, novae are seen across the electromagnetic spectrum, with the origin of the GeV-TeV signature still unknown. Isolation of the nuclear isotopic yield removes will resolve some of the input physics, allowing for a more tractable plasma physics problem.

• Neutron star mergers are the canonical multimessenger transient, whose interpretation is among the most difficult multiphysics problems. The conditions present in the relativistic jet currently cannot be recreated in the lab. However, advances relevant for understanding the radioactively powered kilonova are occurring. The DOE investment in the Facility for Rare Isotope Beams, and similar facilities, will begin to map out the structure of r-process elements for the first time. Properties of excited states of heavy elements can be mapped with current and forthcoming high energy laser facilities. Understanding these events requires observations in gravitational waves and across the electromagnetic spectrum as soon after merger as possible, and characterizing for the subsequent days and weeks afterwards. The NSF Rubin Observatory will prove invaluable given its vast field of view and incredible depth, especially as the NSF LIGO facilities continue to peer deeper into the universe. The observations of the late-time infrared spectrum of a nearby kilonova by NASA’s James Webb Space Telescope give new insights into the ejected material, and confirm a line signature seen in the kilonova following GW170817. We currently cannot robustly identify this atomic or molecular line, in part because of the incomplete tables for the heavier elements. Additionally, the multiphysics issues including high energy density physics, electron/ion energy deposition outside of equilibrium, non-maxwellian electron distributions, and underlying physics must be handled by a relativistic radiation-hydrodynamics model, which is of direct relevance for understanding inertial confinement fusion.

• Collapsars are best known as the origin of long gamma-ray bursts, and are also an additional mechanism to explode a star: the core collapses to a black hole which accretes the heart of the star, result in pair-plasma fireballs at the poles which power jets which explode the star and achieve ultrarelativistic velocities. Studying the pair-plasma fireball properties may be possible with future high intensity laser facilities and groundwork is underway. However, the collapsar mechanism may succeed in exploding a star even if the jet fails to escape. These may be sources of high energy neutrinos detected by NSF’s IceCube Neutrino Observatory. These may be best identified through their mildly or fully relativistic shock breakouts.

This example set covers only a fraction of the physics needed to understand these events, much of the physics relevant for one source class is relevant for others, and only a fraction of astrophysical transients of interest. For example, a key goal in nuclear science is mapping out an equation of state density ladder for matter, where neutron stars occur at the highest density. How matter behaves at this extreme end is relevant for the engines of neutron star mergers and core collapse supernovae. Other transients of interest include, but are not limited to, type I and II X-ray bursts, electron capture supernovae, pair instability supernovae, magnetar flares, fast radio bursts, etc.

Scientific Organizing Committee:

Eric Burns (co-chair)

Chris Fryer (co-chair)

Jennifer Andrews - Astrophysics

Michela Negro - Astrophysics

Francesca Civano - Astrophysics

Julie McEnery - Astrophysics

Aimee Hungerford - Astrophysics, Computation

Michael Murillo - Plasma Physics

Hendrik Schatz - Nuclear Science

Carolyn Kuranz - High-Energy Density Physics 

Daniel Livescu - Fluid Dynamics and Hydrodynamics 

Chris Fontes - Atomic Science

Amy Gall - Atomic Science, Electron Beams

Ed Thomas - Dusty Plasmas 

Fan Guo - Plasma Astrophysics 

Jocelyn Read - Gravity, Dense Matter

Earl Scime - Kinetic Plasma Physics

Local Organizing Committee:

Jeff Blackmon

Eric Burns

Phong Dang

Valerie Milton

Gabriela Gonzalez 

Rob Hynes

Brian Humensky