About

Ira Wasserman is Professor of Astronomy and Physics at Cornell University. He received his B.S. degree from MIT in 1974 and his Ph.D. from Harvard University in 1978, both in physics. After completing his postdoctoral research associate and fellow positions, he joined the Cornell faculty in 1981. His research focuses on relativistic astrophysics, covering topics such as the properties of Type II superconducting cores of neutron stars, the nonlinear development of the r-mode instability of neutron stars and their maximum spin rate, cosmological observations in the inhomogeneous universe, and the birthplaces of cosmic rays. His work also includes theoretical astrophysics related to cosmology, dark energy, the cosmological constant, superstring inflation, and neutron star astrophysics, particularly long-term variations in pulsar rotation. Throughout his career, Wasserman has been recognized with awards such as the NSF Postdoctoral Fellowship and the Alfred P. Sloan Foundation Fellowship. He has held various academic positions at Cornell, progressing from postdoctoral researcher to full professor in both Astronomy and Physics.

Research topics

• Quantum mechanics
• Physics
• Computer Science
• Astrophysics
• Condensed matter physics
• Mathematics
• Classical mechanics
• Mechanics
• Computational physics
• Quantum electrodynamics
• Astronomy

Selected publications

• Numerical Simulation of Electron Magnetohydrodynamics with Landau-quantized Electrons in Magnetar Crusts

  The Astrophysical Journal · 2025-01-23

  articleOpen accessSenior author

  Abstract In magnetar crusts, magnetic fields are sufficiently strong to confine electrons into a small to moderate number of quantized Landau levels. This can have a dramatic effect on the crust's thermodynamic properties, generating field-dependent de Haas–van Alphen oscillations. We previously argued that the large-amplitude oscillations of the magnetic susceptibility could enhance the ohmic dissipation of the magnetic field by continuously generating small-scale, rapidly dissipating field features. This could be important to magnetar field evolution and contribute to their observed higher temperatures. To study this, we performed quasi-3D numerical simulations of electron MHD in a representative volume of neutron star crust matter, for the first time including the magnetization and magnetic susceptibility resulting from Landau quantization. We find that the potential enhancement in the ohmic dissipation rate due to this effect can be a factor ∼3 for temperatures of the order of 10 8 K, and ∼4.5 for temperatures of the order of 5 × 10 7 K, depending on the magnetic field configuration. The nonlinear Hall term is crucial to this amplification: without it, the magnetic field decay is only enhanced by a factor ≲2 even at 5 × 10 7 K. These effects generate a high wavenumber plateau in the magnetic energy spectrum associated with the small-scale de Haas–van Alphen oscillations. Our results suggest that this mechanism could help explain the magnetar heating problem, though due to the effect's temperature-dependence, full magneto-thermal evolution simulations in a realistic stellar model are needed to judge whether it is viable explanation.

  PublisherDOI

• Numerical simulation of electron magnetohydrodynamics with Landau-quantized electrons in magnetar crusts

  arXiv (Cornell University) · 2024-11-12

  preprintOpen accessSenior author

  In magnetar crusts, magnetic fields are sufficiently strong to confine electrons into a small to moderate number of quantized Landau levels. This can have a dramatic effect on the crust's thermodynamic properties, generating field-dependent de Haas--van Alphen oscillations. We previously argued that the large-amplitude oscillations of the magnetic susceptibility could enhance the Ohmic dissipation of the magnetic field by continuously generating small-scale, rapidly dissipating field features. This could be important to magnetar field evolution and contribute to their observed higher temperatures. To study this, we performed quasi-3D numerical simulations of electron MHD in a representative volume of neutron star crust matter, for the first time including the magnetization and magnetic susceptibility resulting from Landau quantization. We find that the potential enhancement in the Ohmic dissipation rate due to this effect can be a factor $\sim 3$ for temperatures of the order of $10^8$ K and $\sim 4.5$ for temperatures of the order of $5\times10^7$ K, depending on the magnetic field configuration. The nonlinear Hall term is crucial to this amplification: without it the magnetic field decay is only enhanced by a factor $\lesssim 2$ even at $5\times10^7$ K. These effects generate a high wavenumber plateau in the magnetic energy spectrum associated with the small-scale de Haas--van Alphen oscillations. Our results suggest that this mechanism could help explain the magnetar heating problem, though due to the effect's temperature-dependence, full magneto-thermal evolution simulations in a realistic stellar model are needed to judge whether it is viable explanation.

  PublisherOA PDFDOI

• Magnetohydrodynamic stability of magnetars in the ultrastrong field regime – II. The crust

  Monthly Notices of the Royal Astronomical Society · 2023-01-13 · 3 citations

  articleOpen accessSenior author

  ABSTRACT We study the stability of Hall magnetohydrodynamic with strong magnetic fields in which Landau quantization of electrons is important. We find that the strong-field Hall modes can be destabilized by the dependence of the differential magnetic susceptibility on magnetic field strength. This hydrodynamic instability, thermodynamic in origin and stabilized by magnetic domain formation, is studied using linear perturbation theory. It is found to have typical growth time of order ≲103 yr, with the growth time decreasing as a function of wavelength of the perturbation. The instability is self-limiting, turning off following a period of local field growth by a few per cent of the initial value. Finite temperature is also shown to limit the instability, with sufficiently high temperatures eliminating it altogether. Alfvén waves can show similar unstable behaviour on shorter time-scales. We find that Ohmic heating due to the large fields developed via the instability and magnetic domain formation is not large enough to account for observed magnetar surface temperatures. However, Ohmic heating is enhanced by the oscillatory differential magnetic susceptibility of Landau-quantized electrons, which could be important to magnetothermal simulations of neutron star crusts.

  PublisherOA PDFDOI

• Nonaxisymmetric Precession of Magnetars and Fast Radio Bursts

  The Astrophysical Journal · 2022 · 17 citations

  1st authorCorresponding
  • Physics
  • Astrophysics
  • Condensed matter physics

  Abstract The repeating fast radio bursts (FRBs) 180916.J0158 and 121102 are visible during periodically occurring windows in time. We consider the constraints on internal magnetic fields and geometries if the cyclical behavior observed for FRB 180916.J0158 and FRB 121102 is due to the precession of magnetars. In order to frustrate vortex line pinning we argue that internal magnetic fields must be stronger than about 10 16 G, which is large enough to prevent superconductivity in the core and destroy the crustal lattice structure. We conjecture that the magnetic field inside precessing magnetars has three components: (1) a dipole component with characteristic strength ∼ 10 14 G; (2) a toroidal component with characteristic strength ∼ 10 15 –10 16 G that only occupies a modest fraction of the stellar volume; and (3) a disordered field with characteristic strength ∼ 10 16 G. The disordered field is primarily responsible for permitting precession, which stops once this field component decays away, which we conjecture happens after ∼1000 yr. Conceivably, as the disordered component damps bursting activity diminishes and eventually ceases. We model the quadrupolar magnetic distortion of the star, which is due to its ordered components primarily, as triaxial and very likely prolate. We address the question of whether the spin frequency ought to be detectable for precessing, bursting magnetars by constructing a specific model in which bursts happen randomly in time with random directions distributed in or between cones relative to a single symmetry axis. Within the context of these specific models, we find that there are precession geometries for which detecting the spin frequency is very unlikely.

  PublisherOA PDFDOI

• Magnetohydrodynamic stability of magnetars in the ultrastrong field regime II: The crust

  arXiv (Cornell University) · 2022-10-11

  preprintOpen accessSenior author

  We study the stability of Hall MHD with strong magnetic fields in which Landau quantization of electrons is important. We find that the strong-field Hall modes can be destabilized by the dependence of the differential magnetic susceptibility on magnetic field strength. This instability is studied using linear perturbation theory, and is found to have typical growth time of order $\lesssim 10^3$ yrs, with the growth time decreasing as a function of wavelength of the perturbation. The instability is self-limiting, turning off following a period of local field growth by a few percent of the initial value. Finite temperature is also shown to limit the instability, with sufficiently high temperatures eliminating it altogether. Alfvén waves can show similar unstable behaviour on shorter timescales. We find that Ohmic heating due to the large fields developed via the instability and magnetic domain formation is not large enough to account for observed magnetar surface temperatures. However, Ohmic heating is enhanced by the oscillatory differential magnetic susceptibility of Landau-quantized electrons, which could be important to magneto-thermal simulations of neutron star crusts.

  PublisherOA PDFDOI

• Empirical Assessment of Aperiodic and Periodic Radio Bursts from Young Precessing Magnetars

  The Astrophysical Journal · 2022 · 6 citations

  • Computer Science
  • Physics
  • Astrophysics

  Abstract We analyze the slow periodicities identified in burst sequences from FRB 121102 and FRB 180916 with periods of about 16 and 160 days, respectively, while also addressing the absence of any fast periodicity that might be associated with the spin of an underlying compact object. Both phenomena can be accounted for by a young, highly magnetized, precessing neutron star that emits beamed radiation with significant imposed phase jitter. Sporadic narrow-beam emission into an overall wide solid angle can account for the necessary phase jitter, but the slow periodicities with 25%–55% duty cycles constrain beam traversals to be significantly smaller. Instead, phase jitter may result from variable emission altitudes that yield large retardation and aberration delays. A detailed arrival time analysis for triaxial precession includes wobble of the radio beam and the likely larger, cyclical torque resulting from the changes in the spin–magnetic moment angle. These effects will confound identification of the fast periodicity in sparse data sets longer than about a quarter of a precession cycle unless fitted for and removed as with orbital fitting. Stochastic spin noise, likely to be much larger than in radio pulsars, may hinder detection of any fast periodicity in data spans longer than a few days. These decoherence effects will dissipate as sources of fast radio bursts age, so they may evolve into objects with properties similar to Galactic magnetars.

  PublisherOA PDFDOI

• Magnetohydrodynamic stability of magnetars in the ultrastrong field regime I: the core

  Monthly Notices of the Royal Astronomical Society · 2021-05-30 · 6 citations

  articleOpen accessSenior author

  ABSTRACT We study magnetohydrodynamic stability of neutron star core matter composed of neutrons, protons, and leptons threaded by a magnetar-strength magnetic field 1014–1017 G, where quantum electrodynamical effects and Landau quantization of fermions are important. Stability is determined using the Friedman–Schutz formalism for the canonical energy of fluid perturbations, which we calculate for a magnetizable fluid with H ≠ B. Using this and the Euler–Heisenberg–Fermi–Dirac Lagrangian for a strongly magnetized fluid of Landau-quantized charged fermions, we calculate the local stability criteria for a neutron star core with a spherical axisymmetric geometry threaded by a toroidal field, accounting for magnetic and composition gradient buoyancy. We find that, for sufficiently strong fields B ≳ 1015 G, the magnetized fluid is unstable to a magnetosonic-type instability with growth times of the order of 10−3 s. The instability is triggered by sharp changes in the second-order field derivative of the Euler–Heisenberg–Fermi–Dirac Lagrangian that occur where additional Landau levels start being populated. These sharp changes are divergent at zero temperature, but are finite for non-zero temperature, so realistic neutron star core temperatures 5 × 107 K < T < 5 × 108 K are used. We conjecture that this mechanism could promote the formation of magnetic domains as predicted by Blandford and Hernquist and Suh and Mathews.

  PublisherOA PDFDOI

• Magnetohydrodynamic stability of magnetars with ultra-strong fields

  Bulletin of the American Physical Society · 2021-04-20

  articleSenior author
  Publisher

• Relativistic finite temperature multifluid hydrodynamics in a neutron star from a variational principle

  Physical review. D/Physical review. D. · 2020 · 25 citations

  Senior authorCorresponding
  • Physics
  • Classical mechanics
  • Quantum electrodynamics

  We develop a relativistic multifluid dynamics appropriate for describing neutron star cores at finite temperatures based on Carter's convective variational procedure. The model includes seven fluids, accounting for both normal and superfluid/superconducting neutrons and protons, leptons (electrons and muons) and entropy. The formulation is compared to the nonvariational relativistic multifluid hydrodynamics of Gusakov and collaborators and shown to be equivalent. Vortex lines and flux tubes, mutual friction, vortex pinning, heat conduction and viscosity are incorporated into the model in steps after the basic hydrodynamics is described. The multifluid system is then considered at the mesoscopic scale where the currents around individual vortex lines and flux tubes are important, and this mesoscopic theory is averaged to determine the detailed vortex line/flux tube contributions to the macroscopic ``effective'' theory. This matching procedure is partially successful, though obtaining full agreement between the averaged mesoscopic and macroscopic effective theory requires discarding subdominant terms. The matching procedure allow us to interpret the magnetic $H$-field inside a neutron star in a way that is consistent with condensed matter physics literature, and to clarify the difference between this interpretation and that in previous astrophysical works.

  PublisherOA PDFDOI

• Magnetic field amplification via protostellar disc dynamos

  Monthly Notices of the Royal Astronomical Society · 2018-03-06

  preprintOpen accessSenior author

  We numerically investigate the generation of a magnetic field in a protostellar disc via an αΩ-dynamo and the resulting magnetohydrodynamic (MHD) driven outflows. We find that for small values of the dimensionless dynamo parameter αd, the poloidal field grows exponentially at a rate |$\sigma \propto \Omega _{\rm K} \sqrt{\alpha _{\rm d}}$|⁠, before saturating to a value |$\propto \sqrt{\alpha _{\rm d}}$|⁠. The dynamo excites dipole and octupole modes, but quadrupole modes are suppressed, because of the symmetries of the seed field. Initial seed fields too weak to launch MHD outflows are found to grow sufficiently to launch winds with observationally relevant mass fluxes of the order of |$10^{-9} \,\mathrm{M}_{{\odot }}\,\rm {yr}^{-1}$| for T Tauri stars. This suggests that αΩ-dynamos may be responsible for generating magnetic fields strong enough to launch observed outflows.

  PublisherOA PDFDOI

Recent grants

• Astronomical Consequences of Fundamental Physics

  NSF · $120k · 2006–2010

• Long Term Variations in the Rotation of Neutron Stars

  NSF · $205k · 2003–2007

• Astronomical Consequences of Fundamental Physics

  NSF · $120k · 2011–2015

• Long Term Variations in the Rotation of Neutron Stars

  NSF · $287k · 2006–2010

Frequent coauthors

• E. E. Salpeter

  25 shared

• Thomas J. Loredo

  Cornell University

  20 shared

• Steven Stack

  Wayne State University

  19 shared

• Éanna É. Flanagan

  Cornell University

  18 shared

• Saul A. Teukolsky

  17 shared

• Stuart L. Shapiro

  17 shared

• J. M. Cordes

  16 shared

• S.-H. Henry Tye

  12 shared

Awards & honors

• NSF Postdoctoral Fellow, 1981-82
• Alfred P. Sloan Foundation Fellow, 1984-88
• Bok Prize Lecturer, Harvard University, 1989