Non-radial oscillation modes in hybrid stars: consequences of a mixed phase

Abstract

We study the possible existence of deconfine quark matter in the core of neutron stars. A relativistic mean field model is used to describe the nuclear matter at low densities while Nambu-Jona-Lasinio model is used to describe the quark matter at high densities. A Gibbs construct is used to describe the quark-hadron phase transition at large densities and at zero temperature. Within the model, as the density is increased, a mixed phase appears at about 2.5 times the nuclear matter saturation density (ρ0) and ends at about 5 ρ0 beyond which pure quark matter phase appear. It turns out that a stable hybrid star of maximum mass, M = 2.27 M with radius R = 14 km, can exist with a quark matter core in a mixed phase only. As the density decreases from the center to the surface, there is a sharp increase of the velocity of sound at the point where the quark-hadron phase transition occurs. This leads to the possibility of low frequency non-radial oscillations, the g modes, in hybrid stars in contrast to canonical neutron stars which do not have such quark matter core. The higher f modes frequencies of neutron stars get enhanced in the presence of quark matter core in hybrid stars. The magnitude of g mode frequencies decrease with increase the repulsive interaction in quark matter.

General relativistic treatment of $f$-mode oscillations of hyperonic stars

“…Hence the empirical relations from past works need to be modified. There are a few efforts to investigate the effect on f -modes of the inclusion of exotic forms of matter (hyperon or quark matter) [52,53,64,65,[76][77][78] or with current astrophysical constraints [79]. However, the works are either limited to selective EoSs or used Cowling approximation to find the mode characteristics.…”

Quasinormal g modes of neutron stars with quarks

“…We also note that while studies of the g-mode abound in the literature, several choose to employ the Cowling approximation [30][31][32]. In fact, the composition g-modes pioneered in the work of Reisenegger and Goldreich [14,15] used Newtonian gravity for simplicity, and subsequent works [31,33,34] used the relativistic Cowling approximation in lieu of a fully general relativistic treatment. There are no extant studies of composition g-modes for realistic neutron or hybrid stars that employ general relativity (GR).…”

Impact of updated multipole Love numbers and f -Love universal relations in the context of binary neutron stars

“…The detection of f-mode characteristics or the postmerger peak frequency f peak can be used to infer the NS EoS, presence of phase transition or even the NS interior composition [48,78,[109][110][111][112][113][114][115][116].Although the detection of f-modes needs the third generation detector sensitivity [34,91], the impact is significant for next observing runs [33]. The detection of f peak becomes more likely in the next observing runs or even with a third generation detector if the merger happens near a supermassive black hole [115].…”