Electromagnetic outflows in a class of scalar-tensor theories: binary neutron star coalescence

TL;DR

This paper investigates whether electromagnetic signals from binary neutron star mergers in certain scalar-tensor theories can serve as an independent test of gravity, complementing gravitational wave observations.

Contribution

It explores electromagnetic signatures in scalar-tensor theories, highlighting potential deviations from General Relativity during neutron star coalescence.

Findings

Electromagnetic flux can differ subtly from GR predictions in these theories.

Electromagnetic observations alone require delicate measurements to distinguish effects.

Coupling electromagnetic data with gravitational waves can improve tests of gravity.

Abstract

As we showed in previous work, the dynamics and gravitational emission of binary neutron star systems in certain scalar-tensor theories can differ significantly from that expected from General Relativity in the coalescing stage. In this work we examine whether the characteristics of the electromagnetic counterparts to these binaries -- driven by magnetosphere interactions prior to the merger event -- can provide an independent way to test gravity in the most strongly dynamical stages of binary mergers. We find that the electromagnetic flux emitted by binaries in these scalar-tensor theories can show deviations from the GR prediction in particular cases. These differences are quite subtle, thus requiring delicate measurements to differentiate between GR and the type of scalar-tensor theories considered in this work using electromagnetic observations alone. However, if coupled with a gravitational-wave detection, electromagnetic measurements might provide a way to increase the confidence with which GR will be confirmed (or ruled out) by gravitational observations.