Hubble constant

n (Astronomy) the rate at which the expansion velocity of the universe depends on distance away. It is currently estimated to lie in the range 60–80 km s^–1 megaparsec^–1. Also called: Hubble parameter

Thesaurus

Noun

Hubble constant - (cosmology) the ratio of the speed of recession of a galaxy (due to the expansion of the universe) to its distance from the observer; the Hubble constant is not actually a constant, but is regarded as measuring the expansion rate todayHubble parameter, Hubble's constant, Hubble's parametercosmogeny, cosmogony, cosmology - the branch of astrophysics that studies the origin and evolution and structure of the universeconstant - a number representing a quantity assumed to have a fixed value in a specified mathematical context; "the velocity of light is a constant"

Translations

costante di Hubble

Hubble constant

Symbol: H ₀. The rate at which the expansion velocity of the Universe changes with distance; it is commonly measured in km s^–1 megaparsec^–1. Current estimates place H ₀ between 60 and 75 km s^–1 Mpc^–1.

The value of H ₀ is derived from the ratio of recession velocity to distance for galaxies beyond the Local Group. The velocity can be measured accurately from the redshift in the galaxy's spectrum. It must be corrected for the Sun's motion (see galactic rotation) and the Virgocentric flow. The main source of dispute over the value of H ₀ comes from the uncertainty of the distances to far-flung galaxies. Refinements in distance measurements have reduced the value since Hubble first determined it (as about 500 km s^–1 Mpc^–1). Uncertainties in large extragalactic distances by a factor of two still leave H ₀ in doubt by the same factor (see distance determination).

The inverse of H ₀ has the dimensions of time and is a measure of the age of an open Universe – the Hubble time (see age of the Universe). In an evolving Universe the Hubble ‘constant’ actually changes with time at a rate dependent upon the deceleration parameter, q ₀. It is independent of time only in a steady-state Universe where q ₀ equals –1. In terms of the cosmic scale factor, R , H ₀ = R ^–1(dR /dt )

See steady-state theory.

Hubble constant

[′həb·əl ‚kän·stənt] (astrophysics) The rate at which the velocity of recession of the galaxies increases with distance; the value is about 70 kilometers per second per megaparsec (or 2.3 × 10^-18 s^-1) with a relative uncertainty of about ± 10%.

Hubble constant

Related to Hubble constant: parsec

noun

Synonyms for Hubble constant

noun (cosmology) the ratio of the speed of recession of a galaxy (due to the expansion of the universe) to its distance from the observer

Synonyms

Hubble parameter
Hubble's constant
Hubble's parameter

Related Words

cosmogeny
cosmogony
cosmology
constant