2/14/2023 0 Comments Quark star![]() ![]() The 2-flavor quark matter is not stable and there is an excess of down. The shock is strong enough to combust nuclear matter to 2-flavor quark matter in the star. The density discontinuity at the quark-hadron boundary initiates a shock wave, which propagates outwards of the star. We show that it is possible to discriminate modified theories of gravity from General Relativity due to the gravitational redshift of the thermal spectrum emerging from the surface of the star. Fluctuation at the neutron star center gives rise to a small deconfined quark core very close to the star center. On the other hand, in conformal scalar-tensor theory, we also have a dilaton sphere (or “disphere”) outside the star but its contribution to gravitational mass for distant observer is negligible. Considering directly f ( R ) gravity, one can say that increasing of mass occurs by the “gravitational sphere” outside the star with some “effective mass”. For distant observers, the gravitational mass of the star increases with increasing α ( α > 0) but the interpretation of this fact depends on frame where we work. The fine-tuning on R is equivalent to the fine-tuning on the scalar field ϕ in this description. We consider also the analogue description in corresponding scalar-tensor gravity. In other words, one needs a fine-tuning for R to achieve quark stars in f ( R ) gravity. Considering scalar curvature R as an independent function, one can find out, for each value of central density, the unique value of central curvature for which one has solutions with the required asymptotic R → 0 for r → ∞. The mass-radius relation for f ( R ) = R + α R 2 model is obtained. Quark star models with realistic equation of state in nonperturbative f ( R ) gravity are considered.
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