Greg Comer, Ph.D.

Professor

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Education

Ph.D. in Physics, University of North Carolina

Research Interests

Comer's main area of research is Newtonian and general relativistic multi-fluid dynamics with applications to astrophysical compact objects (eg. neutron stars) and their gravitational wave emission. The main scientific goal is to understand how superfluidity and superconductivity determine the rotational structure of neutron stars, their spectrum of oscillations, and the extent to which the oscillations result in detectable—-with, say, LIGO—-gravitational waves.

A key question is the role of multiple fluid dynamics on the creation and emission of gravitational waves from neutron stars. Is such dynamics detectable by, say, future versions of LIGO? If yes, then novel aspects of the supranuclear equation of state will be revealed (such as entrainment, which means the momentum of a fluid element inside a neutron star is a linear combination of the fluxes of the independent superfluid/superconducting species). To model multiple fluid dynamics in neutron stars requires input from various areas:

• General relativity and gravitation (neutron star structure, gravitational waves, etc)
• Fluid dynamics (multiple fluxes, dissipation, etc)
• Numerical methods Condensed matter physics (superfluidity/superconductivity, stress calculations, etc)
• Nuclear and particle physics (supranuclear equations of state, reaction rates, etc)

Labs and Facilities

Center for Fluids at All Scales (CFAS) The purpose of CFAS is to promote research and disseminate knowledge on the study of fluids at all physical scales, from the microscopic to the macroscopic. The Center also aims at promoting research on the application of fluid knowledge to various areas of the sciences and engineering. Examples of current research include studies of the micron-sized channels in microfluidic devices and blood vessels, the turbulence found behind parachutes and aircraft (see photo, courtesy of US Army Natick Soldier Center), and the superfluid interiors of neutron stars. CFAS also aims at promoting joint research projects regrouping experts of various disciplines and academic departments.

Publications and Media Placements

Printed Archival Peer-Reviewed Journals
Hawke, I., Comer, G. L., Andersson, N. ”The nonlinear development of the relativistic two-stream instability,” Classical and Quantum Gravity, Volume 30, Issue 14, article id. 145007 (2013). doi: 10.1088/0264-9381/30/14/145007

Haskell, B., Andersson, N., and Comer, G.L., “The Dynamics of Dissipative Multi-fluid Neutron Star Cores,” Physical Review D, v. 86, 063002 (2012). doi: 10.1103/PhysRevD.86.063002

Comer, G.L., Peter, P., and Andersson, N. “Cosmological Two-stream Instability,” Physics Letters B, v. 715, pgs. 289-292 (2012). doi: 10.1016/j.physletb.2012.07.069

Comer, G.L., Peter, P., and Andersson, N. “Two-fluid Cosmology: An Illustration of Fundamental Principles,” Physical Review D, v. 85, 103006 (2012). doi: 10.1103/PhysRevD.85.103006

Andersson, N., and Comer, G.L. “Entropy Entrainment and Dissipation in Finite Temperature Superfluids,” International Journal of Modern Physics D, v. 20, pp. 1215-1233 (2011). doi: 10.1142/S0218271811019396

Andersson, N., and Comer, G.L. “Variational Multi-fluid Dynamics and Causal Heat Conductivity,” Proceedings Royal Society A, online, pp. 1-15 (2009); Proceedings Royal Society A, v. 466 n. 2117, pp. 1373-1387 (2010). doi: 10.1098/rspa.2009.0423

Samuelsson, L., Lopez-Monsalvo, C.S., Andersson, N., and Comer, G.L. “Relativistic Twostream Instability,” General Relativity and Gravitation, pp. 413-433 (2009). doi: 10.1007/s10714-009-0861-3

Lin, L.M., Andersson, N., and Comer, G.L. “Oscillations of General Relativistic Multi-fluid/Multi-Layer Compact Stars,” Physical Review D, v. 78, n. 8, 083008 (2008). doi: 10.1103/PhysRevD.78.083008

Sidery, T.,Andersson, N., and Comer, G.L. “Waves and Instabilities in Dissipative Rotating Superfluid Neutron Stars,” Monthly Notices of Royal Astronomical Society, v. 385, pp. 335-348 (2008). doi: 10.1111/j.1365-2966.2007.12805.x

Andersson, N., Sidery, T., and Comer, G.L., “Superfluid Neutron Star Turbulence,” Monthly Notices of Royal Astronomical Society, v. 381, pp. 747-756 (2007). doi: 10.1111/j.1365-2966.2007.12251.x

Andersson, N., and Comer, G.L. “Relativistic Fluid Dynamics: Physics for Many Different Scales,” Living Reviews in Relativity, v. 10, (2007).

Andersson, N., and Comer, G.L.“A Flux Conservative Formalism for Convective and Dissipative Multi-Fluid Systems, with Application to Newtonian Superfluid Neutron Stars,” Classical and Quantum Gravity, v. 23, pp. 5505–5529 (2006). doi: 10.1088/0264-9381/23/18/003

Andersson, N., and Comer, G.L. and Glampedakis, K. “How Viscous is a Superfluid Neutron Star Core,” Nuclear Physics A, v. 763, pp. 212–229 (2005). doi: 10.1016/j.nuclphysa.2005.08.012

Andersson, N., and Comer, G.L. and Prix, R. “Are Pulsar Glitches Triggered by a Superfluid TwoStream Instability?,” Physical Review Letters, v. 90, n. 9, 091101 (2003). doi: 10.1103/PhysRevLett.90.091101

Andersson, N., and Comer, G.L. and Langlois, D. “Oscillations of General Relativistic Superfluid Neutron Stars,” Physical Review D, v. 66, n. 10, 104002 (2002). doi: 10.1103/PhysRevD.66.104002

Andersson, N., and Comer, G.L. “On the Dynamics of Superfluid Neutron Star Cores,” Monthly Notices of Royal Astronomical Society, v. 328, pp. 1129–1143 (2001). doi: 10.1046/j.1365-8711.2001.04923.x

Andersson, N., and Comer, G.L. “Probing Neutron Star Superfluidity with Gravitational Wave Data,” Physical Review Letters, v. 87, n. 24, 241101 (2001). doi: 10.1103/PhysRevLett.87.241101

Comer, G.L., Langlois, D., and Lin, L.M. “Quasinormal Modes of General Relativistic Superfluid Neutron Stars,” Physical Review D, v. 60, n. 10, 104025 (1999). doi: 10.1103/PhysRevD.60.104025

Comer, G.L., Deruelle, N., Langlois, D., and Parry, J. “Growth or Decay of Cosmological Inhomogeneities as a Function of their Equation of State,” Physical Review D, v. 49, n. 6, pp. 2759–2768 (1994). doi: 10.1103/PhysRevD.49.2759

Brown, J.D., Comer, G.L., Martinez, E.A., Melmed, J., Whiting B.F., and York, J.W. Jr., “Thermodynamic Ensembles and Gravitation,” Classical and Quantum Gravity, v. 7, pp. 1433–1444 (1990). doi: 10.1088/0264-9381/7/8/020

Online Peer-Reviewed Journals
Andersson, N., and Comer, G.L. “Relativistic Fluid Dynamics: Physics for Many Different Scales,” Living Reviews in Relativity, v. 10, (2007).

Honors and Awards

• 2009 2007-08 Society of Physics Students Outstanding Chapter Award (Faculty Advisor)
• 2008 Honorable Mention, SLU Voices “This I Believe” competition
• 2002 SLU Student Government Association Faculty Excellence Award
• 1996 NASA/ASEE Summer Faculty Fellowship, Jet Propulsion Laboratory
• 1995 NASA/ASEE Summer Faculty Fellowship, Jet Propulsion Laboratory
• 1993 Ministry of Foreign Affairs Bourse, Observatiore de Paris-Meudon, France
• 1992 Golda Meir Fellowship, The Hebrew University, Israel

Professional Organizations and Associations

• 2008-present: Member of the Topical Group on Gravitation, American Physical Society
• 2008: Organizing Committee member, 18th Midwest Relativity Meeting, Notre Dame
• 2007: Meeting Organizer, 17th Midwest Relativity Meeting, SLU
• 2006-present: Editor, The Spacetime Emporium, www.compadre.org
• 2006-present: Associate Editor, Matters of Gravity, APS Topical Group in Gravitation
• 2005: Speaker, Las Cumbres Speakers Program
• 1997: Session Chair, 7th Midwest Relativity Meeting, Washington University
• 1994: Session Chair, 4th Midwest Relativity Meeting, SLU
• 1993-present: Referee Duties: Astronomy & Astrophysics, Astrophysics and Space Science, Classical and Quantum Gravity, Entropy, EPSRC in the UK, External Examiner for the Chinese University of Hong Kong, General Relativity and Gravitation, Journal of Mathematical Physics, Journal of Modern Physics A and D, Journal of Physics A, Monthly Notices of Royal Astronomical Society, National Science Foundation, Physics Letters, Physical Review D & Letters, Taylor and Francis Publishing, The Astrophysical Journal, and the US/Armenia CRDF program.
• 1993-present: Member of the American Physical Society
• 1993-present: Member of the American Association of University Professors

Community Work and Service

Comer held a two-year postdoc with the Racah Institute of Physics of The Hebrew University from 1990-92 and a one-year position with the Observatory of Paris-Meudon from 1992-93. He has been on the faculty of Saint Louis University since 1993, and an adjunct faculty with the Department of Physics of Washington University since 1997.

He has published 23 refereed journal articles and 4 non-refereed book chapters, conference proceedings, and on-line arXiv preprints in this area. He is also co-author on an upcoming review on relativistic fluids for the Living Reviews in Relativity. He has also been the principal investigator on two NSF/Gravitational Physics Division grants, a visiting scientist on an EPSERC grant in the United Kingdom and the Chinese University of Hong Kong Program on Initiatives in Numerical Relativity & Astrophysics, and one of the initial recipients of a SLU 2000 Faculty Research Leave Award.