Extremely small stars in scalar-tensor gravity: when stellar radius is less than Schwarzschild one

Abstract

We show analytically that there exist compact stellar objects akin to neutron stars whose radius is smaller than the Schwarzschild radius defined by Arnowitt-Deser-Misner (ADM) mass. The radius of the compact object is defined by the radius where the energy density and the pressure of ordinary matter vanish, while clouds of scalar(s) can extend beyond this radius -- a situation that is often encountered in modified gravity theories, like $F(R)$ gravity and the scalar--Einstein--Gauss-Bonnet gravity. The clouds of scalar mode(s) give additional contributions to the ADM mass and as a result, the corresponding Schwarzschild radius given by the ADM mass can be larger than that of the compact object.

arXiv commentLaTeX, 13 pages, no figure, version to appear in Nuclear Physics B

References in corpus (17)

• Unified cosmic history in modified gravity: from F(R) theory to Lorentz non-invariant models
• Modified Gravity Theories on a Nutshell: Inflation, Bounce and Late-time Evolution
• Relativistic Shapiro delay measurements of an extremely massive millisecond pulsar
• Formation and evaporation of non-singular black holes
• Refined Mass and Geometric Measurements of the High-Mass PSR J0740+6620
• Strange Quark Matter and Compact Stars
• PSR J0952-0607: The Fastest and Heaviest Known Galactic Neutron Star
• The Mass-Radius relation for Neutron Stars in $f(R)$ gravity
• The realistic models of relativistic stars in f(R) = R + alpha R^2 gravity
• On neutron stars in f(R) theories: small radii, large masses and large energy emitted in a merger
• The Radius of PSR J0740+6620 from NICER with NICER Background Estimates
• Avoiding singularities in Lorentzian-Euclidean black holes: the role of atemporality
• The mass-radius relation for neutron stars in $f(R)=R+\alpha R^2$ gravity: a comparison between purely metric and torsion formulations
• Neutron star radius measurement from the ultraviolet and soft X-ray thermal emission of PSR J0437-4715
• Searching for dynamical black holes in various theories of gravity
• Neutron Stars in frames of $R^2$-gravity and Gravitational Waves
• Revisiting compact star in $F(R)$ gravity: Roles of chameleon potential and energy conditions