  In this article we study the hydrostatic equilibrium configuration of neutron
stars (NSs) and strange stars (SSs), whose fluid pressure is computed from the
equations of state $p=\omega\rho^{5/3}$ and $p=0.28(\rho-4{\cal B})$,
respectively, with $\omega$ and ${\cal B}$ being constants and $\rho$ the
energy density of the fluid. We also study white dwarfs (WDs) equilibrium
configurations. We start by deriving the hydrostatic equilibrium equation for
the $f(R,T)$ theory of gravity, with $R$ and $T$ standing for the Ricci scalar
and trace of the energy-momentum tensor, respectively. Such an equation is a
generalization of the one obtained from general relativity, and the latter can
be retrieved for a certain limit of the theory. For the $f(R,T)=R+2\lambda T$
functional form, with $\lambda$ being a constant, we find that some physical
properties of the stars, such as pressure, energy density, mass and radius, are
affected when $\lambda$ is changed. We show that for some particular values of
the constant $\lambda$, some observed objects that are not predicted by General
Relativity theory of gravity can be attained. Moreover, since gravitational
fields are smaller for WDs than for NSs or SSs, the scale parameter $\lambda$
used for WDs is small when compared to the values used for NSs and SSs.

General Relativity and Quantum Cosmology