2020 Section 04), Fall Websign Astronomers believe that the universe is expanding and that stellar objects are moving away from us at a radial velocity v proportional to the distance from Earth to the object.
(a) Write V as a function of D using H as the constant of proportionality
V- HD
(6) The equation in part (a) was first discovered by Edwin Hubble in 1929 and is known as Hubble's law. The constant of proportionality His known as Hubble's constant.
The currently accepted value of Hubble's constant is 70 kilometers per second per megaparsec. (One megaparsec is about 3.086 1099 kilometers.) with these units for
H, the distance D is measured in megaparsecs, and the velocity Vis measured in kilometers per second. The galaxy Arp 220 is about 77 megaparsecs from Earth. How
fast is Arp 220 receding from Earth?
5390
km/sec
(c) One important feature of Hubble's constant is that scientists use it to estimate the age of the universe. The approximate relation is
1012
where y is time in years. Hubble's constant is extremely difficult to measure, and Edwin Hubble's best estimate in 1929 was about 530 kilometers per second per
megaparsec. What is the approximate age of the universe when this value of His used? (Round your answer to one decimal place.)
x billion yr
(d) The calculation in part (c) would give scientists some concern since Earth is thought to be about 4.6 billion years old. What estimate of the age of the universe does
the more modern value of 70 kilometers per second per megaparsec give? (Round your answer to one decimal place.)
322
X billion yr