About

Paul Ricker is a professor in the Department of Astronomy at Illinois College of Liberal Arts & Sciences. His research interests focus on computational astrophysics, with applications to binary stars, galaxy clusters, compact objects, and supernovae. He specializes in parallel numerical algorithm and simulation code development to advance understanding in these areas. Ricker holds a Ph.D. in Physics from The University of Chicago, an M.S.. in Physics from The University of Chicago, and a B.S. in Physics and Astronomy from Pennsylvania State University. He has been recognized with awards such as the Presidential Early Career Award for Scientists and Engineers (PECASE) from the DOE/NNSA and the Gordon Bell Prize. Ricker teaches a range of courses including Introduction to Astronomy, Astrophysics, Computing in Astronomy, Stellar Astrophysics, and Computational Astrophysics and Cosmology. He is also affiliated with the National Center for Supercomputing Applications (NCSA) and serves as a faculty member in the Physics department. His recent publications involve studies on common envelope evolution, active galactic nucleus accretion, planetary nebulae, and multiphysics simulation software.

Research topics

• Physics
• Astrophysics
• Computer Science
• Astronomy
• Quantum mechanics
• Mathematics
• Theoretical physics
• Computational science
• Optics
• Classical mechanics
• Computational physics
• Aerospace engineering
• Operating system
• Distributed computing
• Programming language
• Mathematical analysis
• Telecommunications
• Demography

Selected publications

• The Effect of Donor Star Rejuvenation on Common Envelope Evolution

  The Astrophysical Journal · 2025-01-17 · 9 citations

  articleOpen access

  Abstract In close binary star systems, common envelope evolution (CEE) may occur after a previous phase of mass transfer. Some isolated formation channels for double neutron star binaries suggest that the donor of CEE was the accretor of a previous phase of stable mass transfer. Accretion should substantially alter the structure of the donor, particularly by steepening the density gradient at the core-envelope interface and rejuvenating the star. We study the CEE of a donor that was the accretor of a previous phase of stable mass transfer and has a rejuvenated structure. We perform 3D hydrodynamics simulations of the CEE of an 18 M ⊙ supergiant with a 1.4 M ⊙ companion using rejuvenated and non-rejuvenated 1D stellar models for the donor. We compare the two simulations to characterize the effect of the rejuvenation on the outcome of the common envelope phase and the shape of the ejecta. We find that accounting for a previous phase of mass transfer reduces the duration of the inspiral phase by a factor of two, likely due to the different structures in the outer layers of the donor. In the rejuvenated case, the simulations show more equatorially concentrated and asymmetric ejecta, though both cases display evidence for the formation of a pressure-supported thick circumbinary disk. During the dynamical inspiral phase, the impact of rejuvenation on the unbinding of the envelope is unclear; we find that rejuvenation decreases the amount of unbound mass by 20%–40% depending on the energy criterion used.

  PublisherDOI

• Multidisciplinary Science in the Multimessenger Era

  ArXiv.org · 2025-02-05 · 1 citations

  preprintOpen access

  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, gravity, nuclear science, plasma physics, fluid dynamics and turbulence, computation, particle physics, atomic, molecular, and optical science, condensed matter and materials science, radiation transport, and high energy density physics. This white paper provides an overview of the major scientific advances that lay at the intersection of physics and astronomy and are best probed through time-domain and multimessenger astrophysics, an exploration of how multidisciplinary science can be fostered, and introductory descriptions of the relevant scientific disciplines and key astrophysical sources of interest.

  PublisherOA PDFDOI

• A New Framework for Active Galactic Nucleus Accretion and Jet Feedback in Numerical Simulations

  The Astrophysical Journal Supplement Series · 2025-04-01

  articleOpen accessSenior author

  Abstract Accurate modeling of active galactic nucleus (AGN) feedback, especially due to relativistic jets, is crucial for understanding the cool-core problem in galaxy clusters. We present a new subgrid method to model accretion onto and feedback from AGN in hydrodynamical simulations of galaxy clusters. Instead of applying the traditional Bondi formalism, we use a sink particle algorithm in which the accretion flux is measured directly through a control surface. A weighting kernel is used to reset the gas properties within the accretion radius at the end of each time step. We implement feedback in the form of bipolar jets whose properties are tied to the accretion rate. The method is tested with a spherically symmetric Bondi gas flow problem and a Bondi–Hoyle–Lyttleton wind problem, with and without jet feedback. We discuss the reliability of this model by comparing our jet simulations with those in the literature, and we examine the dependence of test results on parameters such as the resolution and size of the jet injection region. We find that the sink particle model can account for the α factor in accretion measurement, and the accretion radius must be resolved with at least two zones to produce realistic black hole accretion. We also show how underresolving the AGN feedback region in simulations can impact the feedback energy deposited and the jet dynamics. The code described here is the framework for a feedback model, described in a companion paper, that will use accretion disk modeling to more self-consistently determine the feedback efficiency.

  PublisherDOI

• The Effect of Donor Star Rejuvenation on Common Envelope Evolution

  arXiv (Cornell University) · 2024-07-22

  preprintOpen access

  In close binary star systems, common envelope evolution may occur after a previous phase of mass transfer. Some isolated formation channels for double neutron star binaries suggest that the donor of common envelope evolution was the accretor of a previous phase of stable mass transfer. Accretion should substantially alter the structure of the donor, particularly by steepening the density gradient at the core-envelope interface and rejuvenating the star. We study the common envelope evolution of a donor that was the accretor of a previous phase of stable mass transfer and has a rejuvenated structure. We perform 3D hydrodynamics simulations of the common envelope evolution of a 18 $M_\odot$ supergiant with a 1.4 $M_\odot$ companion using rejuvenated and non-rejuvenated 1D stellar models for the donor. We compare the two simulations to characterize the effect of the rejuvenation on the outcome of the common envelope phase and the shape of the ejecta. We find that accounting for a previous phase of mass transfer reduces the duration of the inspiral phase by a factor of two, likely due to the different structure in the outer layers of the donor. In the rejuvenated case, the simulations show more equatorially concentrated and asymmetric ejecta, though both cases display evidence for the formation of a pressure-supported thick circumbinary disk. During the dynamical inspiral phase, the impact of rejuvenation on the unbinding of the envelope is unclear; we find that rejuvenation decreases the amount of unbound mass by 20$\%$ to 40$\%$ depending on the energy criterion used.

  PublisherOA PDFDOI

• Common Envelope Shaping of Planetary Nebulae. IV. From Proto-planetary to Planetary Nebula

  arXiv (Cornell University) · 2022-09-29

  preprintOpen accessSenior author

  We present 2D hydrodynamical simulations of the transition of a proto-planetary nebula to a planetary nebula for central stars in binary systems that have undergone a common envelope event. After 1,000 yr of magnetically driven dynamics (proto-planetary nebula phase), a line-driven stellar wind is introduced into the computational domain and the expansion of the nebula is simulated for another 10,000 yr, including the effects of stellar photoionization. In this study we consider central stars with main sequence (final) masses of 1 (0.569) and 2.5 (0.677) \Mo, together with a 0.6 \Mo ma in sequence companion. Extremely bipolar, narrow-waisted proto-planetary nebulae result in bipolar planetary nebulae, while the rest of the shapes mainly evolve into elliptical planetary nebulae. The initial magnetic field's effects on the collimated structures, such as jets, tend to disappear in most of the cases, leaving behind the remnants of those features in only a few cases. Equatorial zones fragmented mainly by photoionization ( 1 \Mo progenitors), result in ``necklace'' structures made of cometary clumps aligned with the radiation field. On the other hand, fragmentation by photoionization and shocked wind ( 2.5 \Mo progenitors) give rise to the formation of multiple clumps in the latitudinal direction, which remain within the lobes, close to the center, which are immersed and surrounded by hot shocked gas, not necessarily aligned with the radiation field. These results reveal that the fragmentation process has a dependence on the stellar mass progenitor. This fragmentation is made possible by the distribution of gas in the previous post-common envelope proto-planetary nebula as sculpted by the action of the jets.

  PublisherDOI

• Flash-X

  SSRN Electronic Journal · 2022-01-01

  articleOpen access
  PublisherDOI

• Common-envelope shaping of planetary nebulae – IV. From protoplanetary to planetary nebula

  Monthly Notices of the Royal Astronomical Society · 2022-10-03 · 15 citations

  articleOpen accessSenior authorCorresponding

  ABSTRACT We present 2D hydrodynamical simulations of the transition of a protoplanetary nebula (PPN) to a planetary nebula for central stars in binary systems that have undergone a common-envelope event. After 1000 yr of magnetically driven dynamics (PPN phase), a line-driven stellar wind is introduced into the computational domain and the expansion of the nebula is simulated for another 10 000 yr, including the effects of stellar photoionization. In this study we consider central stars with main sequence (final) masses of 1 (0.569) and 2.5 (0.677) M⊙, together with a 0.6-M⊙ main-sequence companion. Extremely bipolar, narrow-waisted PPNe result in bipolar planetary nebulae, while the rest of the shapes mainly evolve into elliptical planetary nebulae. The initial magnetic field’s effects on the collimated structures, such as jets, tend to disappear in most of the cases, leaving behind the remnants of those features in only a few cases. Equatorial zones fragmented mainly by photoionization (1-M⊙progenitors), result in ‘necklace’ structures made of cometary clumps aligned with the radiation field. On the other hand, fragmentation by photoionization and shocked wind (2.5-M⊙progenitors) give rise to the formation of multiple clumps in the latitudinal direction, which remain within the lobes, close to the center, which are immersed and surrounded by hot shocked gas, not necessarily aligned with the radiation field. These results reveal that the fragmentation process has a dependence on the stellar-mass progenitor. This fragmentation is made possible by the distribution of gas in the previous post-common-envelope PPN as sculpted by the action of the jets.

  PublisherOA PDFDOI

• Flash-X: A multiphysics simulation software instrument

  SoftwareX · 2022 · 32 citations

  • Computer Science
  • Computer Science
  • Computational science

  Flash-X is a highly composable multiphysics software system that can be used to simulate physical phenomena in several scientific domains. It derives some of its solvers from FLASH, which was first released in 2000. Flash-X has a new framework that relies on abstractions and asynchronous communications for performance portability across a range of increasingly heterogeneous hardware platforms. Flash-X is meant primarily for solving Eulerian formulations of applications with compressible and/or incompressible reactive flows. It also has a built-in, versatile Lagrangian framework that can be used in many different ways, including implementing tracers, particle-in-cell simulations, and immersed boundary methods.

  PublisherOA PDFDOI

• Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo

  SoftwareX · 2021 · 131 citations

  • Computer Science
  • Computer Science
  • Astronomy
  DOI

• Observation of Gravitational Waves from Two Neutron Star-Black Hole Coalescences

  The Astrophysical Journal Letters · 2021 · 649 citations

  • Physics
  • Astrophysics
  • Astronomy

  We report the observation of gravitational waves from two compact binary coalescences in LIGO's and Virgo's third observing run with properties consistent with neutron star-black hole (NSBH) binaries. The two events are named GW200105_162426 and GW200115_042309, abbreviated as GW200105 and GW200115; the first was observed by LIGO Livingston and Virgo and the second by all three LIGO-Virgo detectors. The source of GW200105 has component masses, whereas the source of GW200115 has component masses and (all measurements quoted at the 90% credible level). The probability that the secondary's mass is below the maximal mass of a neutron star is 89%-96% and 87%-98%, respectively, for GW200105 and GW200115, with the ranges arising from different astrophysical assumptions. The source luminosity distances are and, respectively. The magnitude of the primary spin of GW200105 is less than 0.23 at the 90% credible level, and its orientation is unconstrained. For GW200115, the primary spin has a negative spin projection onto the orbital angular momentum at 88% probability. We are unable to constrain the spin or tidal deformation of the secondary component for either event. We infer an NSBH merger rate density of when assuming that GW200105 and GW200115 are representative of the NSBH population or under the assumption of a broader distribution of component masses. © 2021. The Author(s). Published by the American Astronomical Society.

  DOI

Recent grants

• Investigations of the Common-Envelope Phase of Binary Star Evolution

  NSF · $351k · 2014–2020

Frequent coauthors

• J. van den Brand

  464 shared

• A. Heidmann

  336 shared

• E. Chassande–Mottin

  Laboratoire AstroParticule et Cosmologie

  309 shared

• R. Frey

  304 shared

• T. Briant

  Collège de France

  285 shared

• N. Arnaud

  Université Paris-Saclay

  281 shared

• M. Wąs

  Laboratoire d’Annecy de Physique des Particules

  280 shared

• E. K. Porter

  Université Paris Cité

  277 shared

Education

• PhD, Physics

  University of Chicago

  1996

• MS, Physics

  University of Chicago

  1993

• BS, Physics

  Pennsylvania State University

  1991

Awards & honors

• Presidential Early Career Award for Scientists and Engineers…
• DOE/NNSA Gordon Bell Prize