Activity of Strongly Magnetized Neutron Stars

Extremely dense stellar remnants, known as neutron stars (NS), are not quiet objects. They are known to have quakes in their crusts, which can produce bright bursts of radiation. Like earthquakes allow geologists to study the interior of the Earth, neutron star quakes allow astronomers to probe the star's interior, one of the most important questions in high-energy astrophysics. A research group at Columbia University will use computer simulations to model NS quakes and their interactions with the NS magnetosphere, to better understand observational phenomena such as NS timing glitches, bursts from highly magnetized NS called magnetars, giant NS flares, electromagnetic precursors of neutron star mergers, and perhaps even solve the production of mysterious fast radio bursts (FRBs), which may arise from magnetars. More generally, theoretical astrophysics has a broader impact through promoting knowledge about our universe and through education. The results of the proposed research will be disseminated at conferences and taught as part of high-energy astrophysics course at Columbia University. The research will involve training of graduate and undergraduate students.

First-principle simulations of magnetospheric emission from a quake are novel and will significantly advance the field. The research group has developed a new code that follows the spreading of shear waves excited by a quake into the entire crust, the liquid core, and the magnetosphere. The magnetospheric activity will be examined using an advanced plasma code developed by the group and designed for global kinetic simulations of electron-positron discharge around neutron stars. The proposal has two parts. (1) First-principle simulations of the magnetospheric response to crustal quakes and calculation of the produced radiation. The simulation method will be used to investigate two phenomena: (a) The recently discovered choking of the Vela pulsar during a spin glitch. This observation likely witnessed a powerful starquake. (b) The emission of X-ray bursts by magnetar quakes, a long-standing puzzle. (2) Development of an evolutionary model of young, hyper-active magnetars. These hypothetical objects are plausible engines of cosmological FRBs. The project focuses on the driver of hyper-activity --- ambipolar diffusion in the neutron star core --- and its effect on the magnetosphere, leading to magnetic flares and launching blast waves in the magnetar wind.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.