Solutions to the tethered galaxy problem in an expanding universe and the observation of receding blueshifted objects

Abstract

We use the dynamics of a galaxy, set up initially at a constant proper distance from an observer, to derive and illustrate two counter-intuitive general relativistic results. Although the galaxy does gradually join the expansion of the universe (Hubble flow), it does not necessarily recede from us. In particular, in the currently favored cosmological model, which includes a cosmological constant, the galaxy recedes from the observer as it joins the Hubble flow, but in the previously favored cold dark matter model, the galaxy approaches, passes through the observer, and joins the Hubble flow on the opposite side of the sky. We show that this behavior is consistent with the general relativistic idea that space is expanding and is determined by the acceleration of the expansion of the universe -- not a force or drag associated with the expansion itself. We also show that objects at a constant proper distance will have a nonzero redshift; receding galaxies can be blueshifted and approaching galaxies can be redshifted.

8 pages including 6 figures, to appear in Am. J. Phys., 2003. Reference added in postscript

References in corpus (3)

• Future Island Universes in a Background Universe Accelerated by Cosmological Constant and by Quintessence
• On a probable manifestation of Hubble expansion at the local scales, as inferred from LLR data
• Effects on the structure of the universe of an accelerating expansion

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• Expanding Space: the Root of all Evil?
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• Zero-momentum trajectories inside a black hole and high energy particle collisions
• Graphical and Kinematical Approach to Cosmological Horizons
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• Comments on the tethered galaxy problem
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• Velocities of distant objects in General Relativity revisited
• The Hubble flow: an observer's perspective
• Metric Expansion from Microscopic Dynamics in an Inhomogeneous Universe
• The equivalence principle and the relative velocity of local inertial frames
• Studying the Behavior of Radial Free Geodesics in ΛCDM Model
• Can an Infinitely Long Object Fit in an Expanding Universe?