Question

The Hubble Parameter

The constant describing the rate of this recession, called the Hubble parameterHubble parameterA measure of the rate of expansion of the universe, which is the average value of the velocity of recession divided by distance: about 70 km/s/megaparsec. Hubble parameter A measure of the rate of expansion of the universe, which is the average value of the velocity of recession divided by distance: about 70 km/s/megaparsec. , is used to determine the age and size of the observable universe.

The Hubble parameter, H, indicates the rate at which the universe is expanding, and, thus, can be used to estimate both the universe’s size and age. Therefore, it is very important to determine an accurate value of the Hubble parameter. Note that H has the units of a velocity divided by a distance. The value of H is usually quoted in kilometers per second per megaparsec. Different units will be used for the values of H contained in the two exercises later in this lab, but the units will still be those of a velocity divided by a distance.

There is still some uncertainty over the exact value of H, but most current estimates lie around 71 km/s/Mpc. For calculations in this lab, we shall use the value km/s/Mpc.

Adopting this value for H means that for each megaparsec (Mpc) of distance, the velocity of a distant galaxy appears to increase by 65 kilometers per second. For example, using the Hubble law we would expect that a galaxy at a distance of 2 Mpc from Earth would have a redshift corresponding to a radial velocity of 130 km/s.

For each of the galaxies in the table below calculate the distance from the given radial velocity. For this exercise only: assume a value for Hubble's parameter, H, of 70 km/s/Mpc. Recall that Hubble's Law is given by the relation v Hd Galaxy Radial velocity (km/s) Distance (Mpc) NGC 4402 231 NGC 3506 6321 NGC 2410 4602 NGC 1326 1371 Submit Answer 2 question attempts remaining

Answer 1

Therefore H = 70 km L/M_p C Therefore V = Hd NGC 4402 d = V/H = 231/70 = 33 Mpc NGC 3506 d = V/H = 6321/70 = 90.3 Mpc NGC 2410 d = V/H = 4602/70 = 65.74 Mpc NGC 1326 d/V/H = 1371/70 = 19.59 Mpc