Neutron stars in $$f(\mathtt {R,L_m})$$ gravity with realistic equations of state: joint-constrains with GW170817, massive pulsars, and the PSR J0030+0451 mass-radius from NICER data

Abstract

In this work, we investigate neutron stars (NS) in $$f(\mathtt {R,L_m})$$ f ( R , L m ) theory of gravity for the case $$f(\mathtt {R,L_m})= \mathtt {R}+ \mathtt {L_m}+ \sigma \mathtt {R}\mathtt {L_m}$$ f ( R , L m ) = R + L m + σ R L m , where $$\mathtt {R}$$ R is the Ricci scalar and $$\mathtt {L_m}$$ L m the Lagrangian matter density. In the term $$\sigma \mathtt {R}\mathtt {L_m}$$ σ R L m , $$\sigma $$ 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’s Neutron 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 $$1.4~M_{\odot }$$ 1.4 M ⊙ .

Massive white dwarfs in $$f(\mathtt {R,L_m})$$ gravity

“…Furthermore, one can note from (3), that the four-divergence of the energy-momentum tensor is conserved, which is a remarkable feature of the f (R, L m ) theory for stars with spherical symmetry. The four-divergence conservation of T μν is a consequence of our choice for the matter Lagrangian [50,51], L m = −p, which is consistent with the on-shell Lagrangian for relativistic perfect fluids [73]. Finally we mention that for L m = 0, i.e., the vacuum case in which we also have T μν = 0 and p = 0, the new Einstein equations reduce to G μν + Rg μν /3 = 0.…”

“…For the other cases, σ is assumed to have positive values, going from 0.05 to 0.5 km 2 . The constant presents different values from previous works, where it was larger for neutron stars [50,51], and smaller for weak-field limit [54,55]. As we pointed in our previous works, σ has a dependence on the energy-matter density, i.e., depending on the astrophysical system, the parameter will have a different value.…”

“…In the present work, we are continuing to investigate compact objects in f (R, L m ) gravity, which we have applied in previous works to neutron stars [50,51]. In those works, we showed that this theory can account for the enhancement of the maximum mass in neutron stars, in better agreement with the observational data from GW170817 and NICER as compared to General Relativity [51]. This theory is a generalization of the so-called f (R) theories and was proposed by Harko and Lobo [52].…”

Quark stars with 2.6 $$M_\odot $$ in a non-minimal geometry-matter coupling theory of gravity

“…In fact, the study and analysis of compact objects are of great importance in astrophysics because these objects provide an excellent laboratory to study dense matter in extreme conditions, such as the strong gravity regime. Neutron stars were already studied in f (R, L) gravity, providing a remarkable increase in the maximum mass limit [34,35]. In [34], the matter inside neutron stars was described by a relativistic polytropic equation of state (EoS) and also a Skyrme type EoS known as SLy4.…”

Uniqueness of the Inflationary Higgs Scalar for Neutron Stars and Failure of Non-Inflationary Approximations

“…With regard to astrophysical sources of gravitational waves, neutron stars are in the epicenter of current theoretical and experimental research. This is because neutron stars (NSs) [5][6][7][8][9] are superstars among stars, a wide range of physics research areas must be used to describe these accurately, such as nuclear and high energy physics [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], modified gravity can also describe NSs [25][26][27][28][29][30][31][32][33][34][35][36][37], and theoretical astrophysics [38][39][40][41][42][43][44][45][46][47][48][49]. Four decades passed since the first observation of a NS, and to date serious questions remain regarding the inner structure and physics of NSs.…”