New Class of Quasinormal Modes of Neutron Stars in Scalar-Tensor Gravity

Abstract

Detection of the characteristic spectrum of pulsating neutron stars can be a powerful tool not only to probe the nuclear equation of state but also to test modifications to general relativity. However, the shift in the oscillation spectrum induced by modified theories of gravity is often small and degenerate with our ignorance of the equation of state. In this Letter, we show that the coupling to additional degrees of freedom present in modified theories of gravity can give rise to new families of modes, with no counterpart in general relativity, which could be sufficiently well resolved in frequency space to allow for clear detection. We present a realization of this idea by performing a thorough study of radial oscillations of neutron stars in massless scalar-tensor theories of gravity. We anticipate astrophysical scenarios where the presence of this class of quasinormal modes could be probed with electromagnetic and gravitational wave measurements.

Probing neutron star structure via f -mode oscillations and damping in dynamical spacetime models

“…GW and electromagnetic observations will continue to provide new and detailed information about the nature of neutron star matter. GW observations will shed light on the masses and tidal deformability of neutron stars, while electromagnetic observations will enable accurate measurements of their mass and radius [15] and may even be informative for studies of stellar structure in the context of non-GR spacetimes [29].…”

Probing Crust Meltdown in Inspiraling Binary Neutron Stars

“…If a mode resonance signature is indeed detected (i.e., preferred over the null hypothesis), it is still necessary to compare to other possible origins, such as tidal-p-g coupling [39], dynamical scalarization and vectorization [48,49], scalar modes associated to certain GR extensions [50] and extensions to standard particle physics [51], that predict different δΨðfÞ. Since the crust melting is nearly instant (Fig.…”

Axial quasinormal modes of neutron stars in R2 gravity

“…Therefore the fundamental quadrupole mode has so far only been obtained in the Cowling approximation [46][47][48], where all gravitational degrees of freedom are frozen. Full calculations have only been performed for the radial modes of spontaneously scalarized NSs [49], showing the presence of scalar QNMs in massless STT, and thus an enriched spectrum with respect to GR.…”