The detection of gravitational waves from the merger of two neutron stars in August 2017 was a seminal event for astrophysics. This amalgamation of two extremely dense former stars was associated with a short gamma-ray burst (GRB), making it clear that a merger provides the central engine of the short-duration class of this extraordinarily bright type of astrophysical explosion. In order to better understand how a neutron star merger produces a short GRB, a research collaboration between Purdue University and Princeton University will carry out theoretical and numerical investigations of the merger, with a particular focus on the earliest possible electromagnetic radiation from the merger, the precursor light produced as the neutron stars spiral toward each other before the main event. The researchers will perform simulations of the interacting magnetic fields of merging neutron stars, estimating the power, angular pattern and broadband emission mechanisms, from possible coherent radio waves to X-rays. The project combines research in broad areas of high energy astrophysics and plasma physics. The project addresses diverse problems in multi-messenger astrophysics related to gravitational wave astronomy, interaction of ultra-strong magnetic fields and acceleration of sub-atomic particles. The results of the investigation will also help formulate the strategies for searching for possible merger precursor emission. The research will include involvement of undergraduate students at both universities and an outreach program including animated movies of the interactions being studied.
The most likely scenario to generate precursor emission is the electromagnetic interaction of two neutron stars via the creation of inductive electric fields through the relative motion of magnetized plasma within the common neutron star magnetosphere. It is expected that merger times, at least millions of years after the formation of the second neutron star, are sufficiently long that, at the time of the merger, each magnetosphere is likely to be dead on its own. As the stars spiral in, the magnetospheres can be revived due to the relative orbital motion. The main goal of the project is to study this orbital revival of the common magnetospheres by employing the pulsar magnetosphere paradigm: the generation of the inductive electric field due to the motion of magnetized plasma and ensuing vacuum breakdown. The researchers will consider the formation of gaps: regions with high electric field along magnetic field lines, and reconnection layers in the orbital-modulated common magnetosphere of interacting neutron stars. Spins and orbital motion of the neutron stars may generate conditions favorable for dynamo action within the common magnetosphere, which will amplify the magnetic field. The team will also study the generation of high brightness coherent radio emission via the production of a plasma maser. This project advances the goals of the NSF Windows on the Universe Big Idea.
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.
