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Instead of working with Hubble's constant, a common practice is to introduce the dimensionless Hubble constant, usually denoted by h and commonly referred to as "little h", [29] then to write Hubble's constant H 0 as h × 100 km⋅s −1 ⋅Mpc −1, all the relative uncertainty of the true value of H 0 being then relegated to h. [46]
The observational result of Hubble's law, the proportional relationship between distance and the speed with which a galaxy is moving away from us, usually referred to as redshift, is a product of the cosmic distance ladder. Edwin Hubble observed that fainter galaxies are more redshifted. Finding the value of the Hubble constant was the result ...
For example, 7 × 10 13 h −1 M ☉ = 10 14 h −1 0.70 M ☉. Our best measurement, as of 2013, for the Hubble parameter is h = 0.6780 ± 0.0077 from the Planck mission. In early 2011 it was 0.704 +0.013 −0.014 from WMAP 7-year data. [1] See Hubble's law#Determining the Hubble constant for the most recent value of H 0.
For a derivation see "Appendix A: Standard general relativistic definitions of expansion and horizons" from Davis & Lineweaver 2004. [2] In particular, see eqs . 16–22 in the referenced 2004 paper [note: in that paper the scale factor R ( t ′ ) {\displaystyle R(t')} is defined as a quantity with the dimension of distance while the radial ...
Distance measures are used in physical cosmology to give a natural notion of the distance between two objects or events in the universe.They are often used to tie some observable quantity (such as the luminosity of a distant quasar, the redshift of a distant galaxy, or the angular size of the acoustic peaks in the cosmic microwave background (CMB) power spectrum) to another quantity that is ...
Hubble's law predicts that objects farther than the Hubble horizon are receding faster than light. This outcome is not in violation of special relativity. Since special relativity treats flat spacetimes, it is only valid over small distances within the context of the curved spacetime of the universe.
One application of Hubble's law is to estimate distances to galaxies based on measurements of their recessional velocities. However, for relatively nearby galaxies the peculiar velocity can be comparable to or larger than the recessional velocity, in which case Hubble's law does not give a good estimate of an object's distance based on its ...
Using the Planck units, and the value evaluated in 2025 for the Hubble constant H 0 = 76.5 ± 2.2 (km/s)/Mpc = (2.48 ± 0.07) × 10 −18 s −1, [18] Λ has the value of = = = where is the Planck length. A positive vacuum energy density resulting from a cosmological constant implies a negative pressure, and vice versa.