Causal Limit of Neutron Star Maximum Mass in $f(R)$ Gravity in View of GW190814

Abstract

We investigate the causal limit of maximum mass for stars in the framework of f (R) gravity. We choose a causal equation of state, with variable speed of sound, and with the transition density and pressure corresponding to the SLy equation of state. The transition density is chosen to be equal to twice the saturation density ρt ∼ 2ρ0, and also the analysis is performed for the transition density, chosen to be equal to the saturation density ρt ∼ ρ0. We examine numerically the combined effect of the stiff causal equation of state and of the sound speed on the maximum mass of static neutron stars, in the context of Jordan frame of f (R) gravity. This yields the most extreme upper bound for neutron star masses in the context of extended gravity. As we will evince for the case of R 2 model, the upper causal mass limit lies within, but not deeply in, the mass-gap region, and is marginally the same with the general relativistic causal maximum mass, indicating that the ∼ 3M general relativistic limit is respected. In view of the modified gravity perspective for the secondary component of the GW190814 event, we also discuss the strange star possibility. Using several well established facts for neutron star physics and the Occam's razor approach, although the strange star is exciting, for the moment, it remains a possibility for describing the secondary component of GW190814. We underpin the fact that the secondary component of the compact binary GW190814 is probably a neutron star, a black hole or even a rapidly rotating neutron star, but not a strange star. We also discuss, in general, the potential role of the extended gravity description for the binary merging.

Universal Inflationary Attractors Implications on Static Neutron Stars

“…From this point we shall assume that n = 2, thus let us use the constraints on V 0 from the previous section to determine the values of V 0 always working in Geometrized units with G = 1. By comparing the actions (25) and (38), we have V 0 = 16πV 0 , so V 0 7.62094 × 10 −12 . Hence, since V 0 = U0 ξ 2 , we can choose U 0 = 1 and ξ = 36.2239 × 10 4 , and we can observe that for this choice we shall also explicitly check whether the constraint (33) holds true, in the Jordan frame.…”

“…The last three decades have brought cosmology and astrophysics to the mainstream of physics, since the observation of dark energy [1] and the direct detection of gravitational waves [2,3] have altered the way of thinking on how the Universe works in small and large scales. Neutron stars (NS) [4][5][6][7][8] currently are in the interest of many scientific areas, like nuclear theory [9][10][11][12][13][14][15][16][17][18],, high energy physics [19][20][21][22][23], modified gravity [24][25][26][27][28][29][30][31][32] and astrophysics [33][34][35][36][37][38][39][40].…”

$R^p$ Attractors Static Neutron Star Phenomenology

“…The direct gravitational wave observation GW170817 LIGO & Virgo Collaboration, et al (2017 initiated what is nowadays known as gravitational wave astronomy. Neutron stars (NS) Haensel, Potekhin & Yakovlev (2007); Friedman & Stergioulas (2013); Baym, et al (2018); Lattimer & Prakash (2004); Olmo, Rubiera-Garcia & Wojnar (2020) are at the core of astrophysical gravitational wave observations, and numerous scientific areas are jointly studying NS from their perspective, for example nuclear theory Lattimer (2012); Steiner & Gandolfi (2012) ;Horowitz, et al (2005); Watanabe, Iida & Sato (2000); Shen, et al (1998) ;Xu, et al (2009) ;Hebeler, et al (2013); Mendoza-Temis, et al (2014) ;; Kanakis-Pegios, Koliogiannis & Moustakidis (2020); Tsaloukidis et al (2022), high energy physics Buschmann, et al (2021); Safdi, Sun & Chen (2019) ;Hook, et al (2018); Edwards, et al (2020); Nurmi, Schiappacasse & Yanagida (2021), modified gravity Astashenok, et al ( , 2021; Capozziello, et al (2016); Astashenok, Capozziello & Odintsov (2015; Arapoǧlu, Deliduman & Eksi (2011); Panotopoulos et al (2021); Lobato et al (2020); Numajiri et al (2022) and astrophysics Altiparmak, Ecker & Rezzolla (2022); Bauswein, et al (2020b); Vretinaris, Stergioulas & Bauswein (2020); Bauswein, et al (2020a…”

Maximal Masses of White Dwarfs for Polytropes in $R^2$ Gravity and Theoretical Constraints

“…Usually in this context, neutron stars (NSs) serve as the perfect candidates for studying modified gravity effects at an astrophysical level, and in the literature there exist various works in this research line, see for example, [15][16][17][18][19][20][21][22][23][24][25][26], and for a recent review see [27]. For a simple R 2 gravity, the calculations indicate that the effective gravitational mass of NSs increases although the value of such increase is not large.…”