In this work we investigate the equilibrium configurations of white dwarfs in a modified gravity theory, namely, f(R, T) gravity, for which R and T stand for the Ricci scalar and trace of the energy-m

In this work, we investigate neutron stars (NS) in $$f(\mathtt {R,L_m})$$f(R,Lm) theory of gravity for the case $$f(\mathtt {R,L_m})= \mathtt {R}+ \mathtt {L_m}+ \sigma \mathtt {R}\mathtt {L_m}$$f(R,Lm)=R+Lm+σRLm , where $$\mathtt {R}$$R is the Ricci scalar and $$\mathtt {L_m}$$Lm the Lagrangian matter density. In the term $$\sigma \mathtt {R}\mathtt {L_m}$$σRLm , $$\sigma $$σ represents the coupling between the gravitational and particles fields. For the first time the hydrostatic equilibrium equations in the theory are solved considering realistic equations of state and NS masses and radii obtained are subject to joint constrains from massive pulsars, the gravitational wave event GW170817 and from the PSR J0030+0451 mass-radius from NASA’sNeutron Star Interior Composition Explorer(NICER) data. We show that in this theory of gravity, the mass-radius results can accommodate massive pulsars, while the general theory of relativity can hardly do it. The theory also can explain the observed NS within the radius region constrained by the GW170817 and PSR J0030+0451 observations for masses around $$1.4~M_{\odot }$$1.4M⊙ .

The f(R, T) gravity is a theory whose gravitational action depends arbitrarily on the Ricci scalar, R, and the trace of the stress–energy tensor, T; its field equations also depend on matter Lagrangian, $$\mathscr {L}_{m}$$L m . In the modified theories of gravity where field equations depend on Lagrangian, there is no uniqueness on the Lagrangian definition and the dynamics of the gravitational and matter fields can be different depending on the choice performed. In this work, we have eliminated the $$\mathscr {L}_{m}$$L m dependence from f(R, T) gravity field equations by generalizing the approach of Moraes in Ref. [1]. We also propose a general approach where we argue that the trace of the energy–momentum tensor must be considered an “unknown” variable of the field equations. The trace can only depend on fundamental constants and few inputs from the standard model. Our proposal resolves two limitations: first the energy–momentum tensor of the f(R, T) gravity is not the perfect fluid one; second, the Lagrangian is not well-defined. As a test of our approach we applied it to the study of the matter era in cosmology, and the theory can successfully describe a transition between a decelerated Universe to an accelerated one without the need for dark energy.

This work analyses the hydrostatic equilibrium configurations of strange stars in a non-minimal geometry-matter coupling (GMC) theory of gravity. Those stars are made of strange quark matter, whose distribution is governed by the MIT equation of state. The non-minimal GMC theory is described by the following gravitational action: $$f(R,L)=R/2+L+\sigma RL$$f ( R , L ) = R / 2 + L + σ R L , where R represents the curvature scalar, L is the matter Lagrangian density, and $$\sigma $$σ is the coupling parameter. When considering this theory, the strange stars become larger and more massive. In particular, when $$\sigma =50$$σ = 50 km $$^2$$2 , the theory can achieve the 2.6 $$M_\odot $$M ⊙ , which is suitable for describing the pulsars PSR J2215+5135 and PSR J1614-2230, and the mass of the secondary object in the GW190814 event. The 2.6 $$M_\odot $$M ⊙ is a value hardly achievable in General Relativity, even considering fast rotation effects, and is also compatible with the mass of PSR J0952-0607 ( $$M = 2.35 \pm 0.17 ~M_\odot $$M = 2.35 ± 0.17 M ⊙ ), the heaviest and fastest pulsar in the disk of the Milky Way, recently measured, supporting the possible existence of strange quark matter in its composition. The non-minimal GMC theory can also give feasible results to describe the macroscopical features of strange star candidates.