Magnetohydrodynamic simulations of compact stars and binaries in full general relativity

Sun, Lunan

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https://hdl.handle.net/2142/117706 Copy

Description

Title

Magnetohydrodynamic simulations of compact stars and binaries in full general relativity

Author(s)

Sun, Lunan

Issue Date

2022-08-17

Director of Research (if dissertation) or Advisor (if thesis)

Shapiro, Stuart L

Doctoral Committee Chair(s)

Gammie, Charles F

Committee Member(s)

• Fields, Brian D
• Filippini, Jeffery P

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• General Relativity
• Numerical Relativity
• MHD
• Astrophysics
• Black Hole
• Neutron Stars
• Neutrino Transport
• Computational Physics

Abstract

For years, the original Illinois GRMHD code developed by the Illinois Relativity Group has been used to study numerous interesting and insightful astrophysical systems in strong gravity and magnetic fields. Employing this code, for example, we performed fully general relativistic, magnetohydrodynamic (GRMHD) simulations of marginally stable, radiation-dominated stars with various magnetic field configurations (unmagnetized, interior-only, and pulsar-like), equations of state (EOSs) (Γ ≳ 4/3, n ≲ 3 polytropes), rotation profiles (uniform and differential rotation), and gas-pressure perturbations. The work is motivated by the unknown origin of the accreting supermassive black holes (SMBHs), which are believed to be the engines that power quasars and active galactic nuclei (AGNs). We also constructed the first dynamically stable, extremely compact neutron star (NS) that contains an ergoregion, a region in which there are no timelike static observers, with a compressible, causal EOS. This exotic model may provide an alternative mechanism for powering short γ-ray bursts (sGRBs), as well as provide potential compact binary candidates inside the mass gap (3 − 5M⊙). This thesis will focus on our most recent, GRMHD simulations of merging binary neutron stars that incorporate both neutrino transport and magnetic fields. Our new radiative transport module for neutrinos adopts a general relativistic, truncated-moment (M1) formalism. The binaries consist of two identical, irrotational stars modeled by the SLy nuclear equation of state(EOS). They are initially in quasicircular orbit and threaded with a poloidal dipole magnetic field that extends from the stellar interior into the exterior, as in typical pulsars. We insert neutrino processes shortly after the merger and focus on the role of neutrinos in launching a jet following the collapse of the hypermassive neutron star (HMNS) remnant to a spinning black hole (BH). We treat two microphysical versions: one (a “warm-up”) evolving a single neutrino species and considering only charged-current processes, and the other evolving three species (νe,ν ̄e,νx) and their related processes. We track the evolution until the system reaches a quasiequilibrium state after BH formation. We find that the BH + disk remnant eventually launches an incipient jet. The electromagnetic Poynting luminosity is ~ 10^{53} erg s^{−1}, consistent with that of typical sGRBs. The effect of neutrino cooling shortens the lifetime of the HMNS and lowers the amplitude of the major peak of the gravitational wave (GW) power spectrum somewhat. After BH formation, neutrinos help clear out the matter near the BH poles, resulting in lower baryon-loaded surrounding debris. The neutrino luminosity resides in the range ~ 10^{52−53} erg s^{−1} once quasiequilibrium is achieved. Comparing with the neutrino-free models, we observe that the inclusion of neutrinos yields similar ejecta masses and is inefficient in carrying off additional angular momentum.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Lunan Sun

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