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Browsing Articles by Subject "astrophysics"

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    Note on the effect of a massive accretion disk in the measurements of black hole spins
    (2014-06-25) Bambi, Cosimo; Malafarina, D.; Tsukamoto, Naoki
    The spin measurement of black holes has important implications in physics and astrophysics. Regardless of the specific technique to estimate the black hole spin, all the current approaches assume that the space-time geometry around the compact object is exactly described by the Kerr solution. This is clearly an approximation, because the Kerr metric is a stationary solution of the vacuum Einstein equations. In this paper, we estimate the effect of a massive accretion disk in the measurement of the black hole spin with a simple analytical model. For typical accretion disks, the mass of the disk is completely negligible, even for future more accurate measurements. However, for systems with very massive disks the effect may not be ignored.
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    ItemOpen Access
    The general solution for relativistic spherical shells
    (2005) Kijowski, J.; Magli, G.; Malafarina, D.
    The general exact solution of the Einstein-matter field equations describing spherically symmetric shells satisfying an equation of state in closed form is discussed under general assumptions of physical reasonableness. The solutions split into two classes: a class of “astrophysically interesting” solutions describing “ordinary” matter with positive density and pressure, and a class of “phantom-like” solutions with positive density but negative active gravitational mass, which can also be of interest in several “very strong fields” regimes. Known results on linear-barotropic equations of state are recovered as particular cases.