deceleration parameter concept from the Astronomy knowledge base

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deceleration parameter
(q₀)

subject fact

deceleration parameter has symbol q₀ has source: Hawley, J.F., Halcomb, K.H. 1998 Foundations of Modern Cosmology, Oxford University Press, 2001-09-27 09:32:59.0
has definition Quantity designating the rate at which the expansion of the universe is slowing down, owing to the braking effect of the galaxies' gravitational tug on one another. It is a function of the cosmic matter density. has source: Ferris, T. 1988 Coming of Age in the Milky Way, Morrow, 2001-09-27 09:32:59.0
has definition A parameter that measures the rate of slowing down of the expansion of the universe. Gravity causes the slowing down. The deceleration parameter equals omega (another cosmological parameter) when the universe is dominated by radiation, approximately the first 100000 years after the big bang, and 1/2 omega when the universe is dominated by matter. Since the deceleration parameter is equivalent to omega (assuming a cosmological constant of zero, as often done), it determines the ultimate fate and spatial geometry of the universe. The deceleration parameter is often denoted by the symbol q₀. (See omega.) has source: Lightman, A., Brawer, R. 1990 The Lives and Worlds of Modern Cosmologists, Harvard University Press, 2001-09-27 09:32:59.0
has definition A dimensionless quantity describing the rate at which the expansion of the Universe is slowing down because of self-gravitation: it gives a measure of the matter density. In Friedmann's equation (which describes many cosmological models) q₀ = - 1 indicates a steady-state universe, q₀ < +1/2 indicates an open universe, q₀ = +1/2 indicates a flat Euclidean universe, and q₀ > 1/2 indicates a universe that is decelerating and will eventually contract. Sandage and Tammann (1975) obtain q₀ = 0.10 for H₀ = 55 km s^-1 Mpc^-1. has source: Hopkins, J. 1976 Glossary of Astronomy and Astrophysics, University of Chicago Press, 2001-09-27 09:32:59.0
has definition A parameter (that denotes the rate of change with time of the Hubble constant. has source: Hawley, J.F., Halcomb, K.H. 1998 Foundations of Modern Cosmology, Oxford University Press, 2001-09-27 09:32:59.0
is an instance of astronomical constant

number has value 2001-09-27 09:32:57.0

deceleration parameter	has symbol q₀
	has definition Quantity designating the rate at which the expansion of the universe is slowing down, owing to the braking effect of the galaxies' gravitational tug on one another. It is a function of the cosmic matter density.
	has definition A parameter that measures the rate of slowing down of the expansion of the universe. Gravity causes the slowing down. The deceleration parameter equals omega (another cosmological parameter) when the universe is dominated by radiation, approximately the first 100000 years after the big bang, and 1/2 omega when the universe is dominated by matter. Since the deceleration parameter is equivalent to omega (assuming a cosmological constant of zero, as often done), it determines the ultimate fate and spatial geometry of the universe. The deceleration parameter is often denoted by the symbol q₀. (See omega.)
	has definition A dimensionless quantity describing the rate at which the expansion of the Universe is slowing down because of self-gravitation: it gives a measure of the matter density. In Friedmann's equation (which describes many cosmological models) q₀ = - 1 indicates a steady-state universe, q₀ < +1/2 indicates an open universe, q₀ = +1/2 indicates a flat Euclidean universe, and q₀ > 1/2 indicates a universe that is decelerating and will eventually contract. Sandage and Tammann (1975) obtain q₀ = 0.10 for H₀ = 55 km s^-1 Mpc^-1.
	has definition A parameter (that denotes the rate of change with time of the Hubble constant.
	is an instance of astronomical constant
number	has value