Time evolution of pulsar obliquity angle from 3D simulations of magnetospheres

Alexander Philippov*, Alexander Tchekhovskoy, Jason G. Li

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

73 Scopus citations


The rotational period of isolated pulsars increases over time due to the extraction of angular momentum by electromagnetic torques. These torques also change the obliquity angle α between the magnetic and rotational axes. Although actual pulsar magnetospheres are plasma filled, the time evolution of α has mostly been studied for vacuum pulsar magnetospheres. In this work, we self-consistently account for the plasma effects for the first time by analysing the results of time-dependent 3D force-free and magnetohydrodynamic simulations of pulsar magnetospheres. We show that if a neutron star is spherically symmetric and is embedded with a dipolar magnetic moment, the pulsar evolves so as to minimize its spin-down luminosity: both vacuum and plasma-filled pulsars evolve towards the aligned configuration (α = 0). However, they approach the alignment in qualitatively different ways. Vacuum pulsars come into alignment exponentially fast, with α α exp (-t/τ) and τ ~ spin-down time-scale. In contrast, we find that plasma-filled pulsars align much more slowly, with α α (t/τ)-1/2. We argue that the slow time evolution of obliquity of plasma-filled pulsars can potentially resolve several observational puzzles, including the origin of normal pulsars with periods of ~1 s, the evidence that oblique pulsars come into alignment over a time-scale of ~107 yr, and the observed deficit, relative to an isotropic obliquity distribution, of pulsars showing interpulse emission.

Original languageEnglish (US)
Pages (from-to)1879-1887
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Jun 2014


  • Pulsars: General
  • Stars: Magnetic field
  • Stars: Neutron
  • Stars: Rotation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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