Self-Consistent Pulsar Magnetosphere Models:Macroscopic and Kinetic Models in the FERMI Era

University Of Maryland, College Park, College Park MD

Investigators

Abstract

"Neutron stars" pack the mass of our Sun into a volume the size of Manhattan Island. Because the density is so high, individual atomic nuclei crowd against each other and dissolve into neutrons. In the 1960s, radio astronomers discovered pulsating radio sources. Scientists soon realized that these "pulsars" are rapidly rotating neutron stars. Their rotation periods range from a few seconds down to several thousandths of a second. Magnetic fields more than a trillion times stronger than Earth's magnetic field are "frozen" into the neutron star, causing the pulsar radio emission. The actual mechanism responsible for generating these radio signals has remained a mystery for nearly half a century. Within the past decade, observations using the Fermi spacecraft have revealed more than 100 pulsars that emit pulsed gamma rays as well as pulsed radio signals. The Investigators propose to compute detailed, three-dimensional numerical models for the behavior of electrons and positrons (positively charged electrons) in the space surrounding a pulsar. Their research will attempt to produce the first self-consistent models of these so-called "pulsar magnetospheres." The goal of this research is to enable scientists to predict the full spectrum of emission from a pulsar. This will allow them to test the theory against observations. If successful, these results will provide very strong Intellectual Impact from this work. The Broader Impacts derive from the Investigators' activities to promote STEM education at several levels and from an innovative use of 3D printing to fabricate 3D models of pulsar magnetospheres. As noted above, pulsars are rapidly rotating neutron stars, with enormously strong magnetic fields. Astrophysicists quickly determined that such strong fields, "frozen" into rapidly rotating stars, would radiate electromagnetic energy at very high rates. Observations from the Fermi Gamma-Ray Space Telescope within the past decade have now detected gamma radiation from more than 100 pulsars, and preliminary work by the Investigators has demonstrated remarkable success in generating gamma-ray lightcurves that can be compared with these observations. The proposed research will employ several up-to-date computer codes to attack the complicated problem of the pulsar emission mechanism through three-dimensional numerical simulations of pulsar magnetospheres. The project will combine computations of the microscopic behavior of the plasma particles using particle-in-cell (PIC) methods with computations of the large-scale plasma behavior using magnetohydrodynamic (MHD) simulations in an effort to develop fully self-consistent three-dimensional models. The Intellectual Impact of the project results from the fact that, if it is successful, this work will constitute a valuable step forward in our understanding of pulsars. The Broader Impacts of the work derive from the PIs' activities to promote STEM education at several levels and from innovative use of 3D printing to fabricate 3D models of pulsar magnetospheres.