The Hubble law shows the relationship between the mass of a galaxy a.pdf

The Hubble law shows the relationship between the mass of a galaxy and its distance.
Solution
The distant galaxies we see in all directions are moving away from the Earth, as evidenced by
their red shifts. Hubble\'s law describes this expansion. The fact that we see other galaxies
moving away from us doesnotimply that we are the center of the universe!Allgalaxies will see
other galaxies moving away from them in an expanding universe unless the other galaxies are
part of the same gravitationally bound group or cluster of galaxies. A rising loaf of raisin bread is
a good visual model: each raisin will see all other raisins moving away from it as the loaf
expands.
The fact that the universe is expanding then raises the question \"Will it always expand?\" Since
the action of gravity works against the expansion, then if the density were large enough, the
expansion would stop and the universe would collapse in a \"big crunch\". This is called a closed
universe. If the density were small enough, the expansion would continue forever (an open
universe). At a certain precise critical density, the universe would asymtotically approach zero
expansion rate, but never collapse. Remarkably, all evidence indicates that the universe is very
close to that critical density. Discussions about the expansion of the universe often refer to
adensity parameter which is the density divided by the critical density, such that = 1 represents
the critical density condition.
Hubble\'s Law
Hubble\'s law is a statement of a direct correlation between the distance to a galaxy and its
recessional velocity as determined by the red shift. It can be stated as
v = H0r, v= recessional velocity, H0=Hubble constant, r=distance.
Hubble Parameter
The proportionality between recession velocity and distance in the Hubble Law is called the
Hubble constant, or more appropriately the Hubble parameter since it does depend upon time. In
recent years the value of the Hubble parameter has been considerably refined, and the current
value given by the WMAP mission is 71 km/s per megaparsec.
The recession velocities of distant galaxies are known from the red shift, but the distances are
much more uncertain. Distance measurement to nearby galaxies uses Cepheid variables as the
main standard candle, but more distant galaxies must be examined to determine the Hubble
constant since the direct Cepheid distances are all within the range of the gravitational pull of the
local cluster. Use of the Hubble Space Telescope has permitted the detection of Cepheid
variables in the Virgo cluster which have contributed to refinement of the distance scale.
The Particle Data Group documents quote a \"best modern value\" of the Hubble constant as 72
km/s per megaparsec (+/- 10%). This value comes from the use of type Ia supernovae (which
give relative distances to about 5%) along with data from Cepheid variables gathered by the
Hubble Space Telescope. The value from the WMAP survey is 71 km/s per megaparsec..

1. The Hubble law shows the relationship between the mass of a galaxy and its distance.

Solution

The distant galaxies we see in all directions are moving away from the Earth, as evidenced by
their red shifts. Hubble\'s law describes this expansion. The fact that we see other galaxies
moving away from us doesnotimply that we are the center of the universe!Allgalaxies will see
other galaxies moving away from them in an expanding universe unless the other galaxies are
part of the same gravitationally bound group or cluster of galaxies. A rising loaf of raisin bread is
a good visual model: each raisin will see all other raisins moving away from it as the loaf
expands.
The fact that the universe is expanding then raises the question \"Will it always expand?\" Since
the action of gravity works against the expansion, then if the density were large enough, the
expansion would stop and the universe would collapse in a \"big crunch\". This is called a closed
universe. If the density were small enough, the expansion would continue forever (an open
universe). At a certain precise critical density, the universe would asymtotically approach zero
expansion rate, but never collapse. Remarkably, all evidence indicates that the universe is very
close to that critical density. Discussions about the expansion of the universe often refer to
adensity parameter which is the density divided by the critical density, such that = 1 represents
the critical density condition.
Hubble\'s Law
Hubble\'s law is a statement of a direct correlation between the distance to a galaxy and its
recessional velocity as determined by the red shift. It can be stated as
v = H0r, v= recessional velocity, H0=Hubble constant, r=distance.
Hubble Parameter
The proportionality between recession velocity and distance in the Hubble Law is called the
Hubble constant, or more appropriately the Hubble parameter since it does depend upon time. In
recent years the value of the Hubble parameter has been considerably refined, and the current
value given by the WMAP mission is 71 km/s per megaparsec.
The recession velocities of distant galaxies are known from the red shift, but the distances are
much more uncertain. Distance measurement to nearby galaxies uses Cepheid variables as the
main standard candle, but more distant galaxies must be examined to determine the Hubble
constant since the direct Cepheid distances are all within the range of the gravitational pull of the
local cluster. Use of the Hubble Space Telescope has permitted the detection of Cepheid
variables in the Virgo cluster which have contributed to refinement of the distance scale.

2. The Particle Data Group documents quote a \"best modern value\" of the Hubble constant as 72
km/s per megaparsec (+/- 10%). This value comes from the use of type Ia supernovae (which
give relative distances to about 5%) along with data from Cepheid variables gathered by the
Hubble Space Telescope. The value from the WMAP survey is 71 km/s per megaparsec.