Schwarzschild De Sitter Metric

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Yukterez
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Schwarzschild De Sitter Metric

Beitragvon Yukterez » Mo 17. Feb 2020, 21:32

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The Schwarzschild De Sitter metric can be used to study the gravity of a dominant mass in an expanding universe:

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The critical mass at which the black hole horizon coincides with the cosmic event horizon is

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where the radii of the horizons are derived by setting

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to 0 and solving for the positive solutions for r.
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The maximal mass of a black hole in a De Sitter universe with our cosmological constant that is Λ≈1e-52/m² would be approximately 4.3e52kg:               
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x-axis: M (in kg), y-axis: r (in GLyr); blue: horizons (cosmic event horizon and black hole horizon), red: Schwarzschild radius rs
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The attraction of a galaxy like ours is offset by the expansion of the universe at a distance of about 1 megaparsec, so that a test particle that is at that distance from the galaxy is attracted by it as much as it is accelerated away from it by the dark energy.

The physical distance of a test particle from the dominant mass remains constant at the critical radius (while the distance in co-moving coordinates is shrinking). If the dominant mass rests relative to the background radiation, i.e. flows with the Hubbleflow, our stationary test particle can no longer also rest relative to the background radiation, since it is not flowing with the Hubble flow when it is stationary with respect to the central mass.

Critical radius: the neutonian orbital velocity is set equal to the vacuum recession velocity and resolved to r:

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Derivation: the critical radius at which a test particle remains stationary relative to the dominant mass is, with

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and the resulting radial component of the four-acceleration

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which is set to 0 and resolved to r, at

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In a De Sitter universe, the relation between the Hubble constant and the cosmological constant is

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plugging that into the solution for the critical radius, we get the solution obtained above

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The local escape velocity relative to a stationary buoy is with

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or E=-pt=mc² and resolved to v

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where the minimum is always greater than 0 and lies at the critical radius mentioned above, where it is

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For an observer who is traveling with the escape velocity, the gravitational and the kinematic time dilation balance out, so that

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Recessional velocity of free-falling test particles that arise near the critical radius (in natural units of G=M=c=1 und Λ=0.01):

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x-axis: r (in GM/c²), y-axis: v (in c); red: recessional velocity relative to stationary Fidos, green: escape velocity. Λ=c⁴/G²/M²/100=1/rs²/25
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The worksheets (.nb format) can be downloaded by clicking on the respective image. Complete equations of motion: ssds.html, Related topic: SE
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Simon Tyran aka Симон Тыран @ minds || vk || wikipedia || stackexchange || wolframBild

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