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Register a new userStudy of the charged super-Chandrasekhar limiting mass white dwarfs in the $f(R,mathcal{T})$ gravity
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The equilibrium configuration of white dwarfs composed of a charged perfect fluid are investigated in the context of the $f(R,mathcal{T})$ gravity, for which $R$ and $mathcal{T}$ stand for the Ricci scalar and the trace of the energy-momentum tensor, respectively. By considering the functional form $f(R, mathcal{T})=R+2chi mathcal{T}$, where $chi$ is the matter-geometry coupling constant, and for a Gaussian ansatz for the electric distribution, some physical properties of charged white dwarfs were derived, namely: mass, radius, charge, electric field, effective pressure and energy density; their dependence on the parameter $chi$ was also derived. In particular, the $chi$ value important for the equilibrium configurations of charged white dwarfs has the same scale of $10^{-4}$ of that for non-charged stars and the order of the charge was $10^{20}$C, which is scales with the value of one solar mass, i.e., $sqrt{G}M_odotsim 10^{20}$C. We have also shown that charged white dwarf stars in the context of the $f(R,mathcal{T})$ have surface electric fields generally below the Schwinger limit of $1.3times 10^{18}$V/m. In particular, a striking feature of the coupling between the effects of charge and $f(R,mathcal{T})$ gravity theory is that the modifications in the background gravity increase the stellar radius, which in turn diminishes the surface electric field, thus enhancing stellar stability of charged stars. Most importantly, our study reveals that the present $f(R,T)$ gravity model can suitably explain the super-Chandrasekhar limiting mass white dwarfs, which are supposed to be the reason behind the over-luminous SNeIa and remain mostly unexplained in the background of general relativity (GR).
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After the prediction of many sub- and super-Chandrasekhar (at least a dozen for the latter) limiting mass white dwarfs, hence apparently peculiar class of white dwarfs, from the observations of luminosity of type Ia supernovae, researchers have proposed various models to explain these two classes of white dwarfs separately. We earlier showed that these two peculiar classes of white dwarfs, along with the regular white dwarfs, can be explained by a single form of the f(R) gravity, whose effect is significant only in the high-density regime, and it almost vanishes in the low-density regime. However, since there is no direct detection of such white dwarfs, it is difficult to single out one specific theory from the zoo of modified theories of gravity. We discuss the possibility of direct detection of such white dwarfs in gravitational wave astronomy. It is well-known that in f(R) gravity, more than two polarization modes are present. We estimate the amplitudes of all the relevant modes for the peculiar as well as the regular white dwarfs. We further discuss the possibility of their detections through future-based gravitational wave detectors, such as LISA, ALIA, DECIGO, BBO, or Einstein Telescope, and thereby put constraints or rule out various modified theories of gravity. This exploration links the theory with possible observations through gravitational wave in f(R) gravity.
The idea of possible modification to gravity theory, whether it is in the Newtonian or general relativistic premises, is there for quite sometime. Based on it, astrophysical and cosmological problems are targeted to solve. But none of the Newtonian theories of modification has been performed from the first principle. Here, we modify Poissons equation and propose two possible ways to modify the law gravitation which, however, reduces to Newtons law far away from the center of source. Based on these modified Newtons laws, we attempt to solve problems lying with white dwarfs. There are observational evidences for possible violation of the Chandrasekhar mass-limit significantly: it could be sub- as well as super-Chandrasekhar. We show that modified Newtons law, either by modifying LHS or RHS of Poissons equation, can explain them.
Since 2012, we have initiated a new idea showing that the mass of highly magnetized or modified Einsteins gravity induced white dwarfs could be significantly super-Chandrasekhar with a different mass-limit. This discovery has several important consequences, including explanation of peculiar, over-luminous type Ia supernovae, soft gamma-ray repeaters and anomalous X-ray pulsars without invoking extraordinarily strong, yet unobserved, magnetic fields. It further argues for a possible second standard candle. Based on simpler calculations, these white dwarfs are also shown to be much less luminous than their standard counter-parts (of low magnetic fields). This discovery altogether initiates a new field of research.
In this work we investigate the equilibrium configurations of white dwarfs in a modified gravity theory, na-mely, $f(R,T)$ gravity, for which $R$ and $T$ stand for the Ricci scalar and trace of the energy-momentum tensor, respectively. Considering the functional form $f(R,T)=R+2lambda T$, with $lambda$ being a constant, we obtain the hydrostatic equilibrium equation for the theory. Some physical properties of white dwarfs, such as: mass, radius, pressure and energy density, as well as their dependence on the parameter $lambda$ are derived. More massive and larger white dwarfs are found for negative values of $lambda$ when it decreases. The equilibrium configurations predict a maximum mass limit for white dwarfs slightly above the Chandrasekhar limit, with larger radii and lower central densities when compared to standard gravity outcomes. The most important effect of $f(R,T)$ theory for massive white dwarfs is the increase of the radius in comparison with GR and also $f(R)$ results. By comparing our results with some observational data of massive white dwarfs we also find a lower limit for $lambda$, namely, $lambda >- 3times 10^{-4}$.
We study strange stars in the framework of $fleft(R,mathcal{T}right)$ theory of gravity where the strange quark matter distribution inside the stellar system is governed by the phenomenological MIT Bag model equation of state (EOS). Further, for a specific value of $B$ and observed values of mass of the strange star candidates we obtain the exact solution of the modified Tolman-Oppenheimer-Volkoff (TOV) equation in the framework of $fleft(R,mathcal{T}right)$ gravity and have studied in detail the dependence of the different physical parameters due to the chosen different values of $chi$. To check the physical acceptability and stability of the stellar system based on the obtained solutions we have performed different physical tests, viz., the energy conditions, Herrera cracking concept, adiabatic index etc. In this work, we also have explained the effects, those are arising due to the interaction between the matter and the curvature terms in $fleft(R,mathcal{T}right)$ gravity, on the anisotropic compact stellar system. It is interesting to note that as the values of $chi$ increase the strange stars become more massive and their radius increase gradually so that eventually they gradually turn into less dense compact objects. The present study reveals that the modified $fleft(R,mathcal{T}right)$ gravity is a suitable theory to explain massive stellar systems like recent magnetars, massive pulsars and super-Chandrasekhar stars, which can not be explained in the framework of GR. However, for $chi=0$ the standard results of Einsteinian gravity are retrieved.
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