The mass of the Sun is 2 ∙ 1030 kg, and the Sun contains more than 99% of all the mass in the Solar System. Astronomers estimate there are approximately 100 billion stars in the Milky Way and approximately 100 billion galaxies in the universe. The Sun and other stars arc predominantly composed of hydrogen; a hydrogen atom has a mass of approximately 2 ∙ 10-27kg.
a) Assuming that the Sun is an average star and the Milky Way is an average galaxy, what is the total mass of the universe?
b) Since the universe consists mainly of hydrogen, can you estimate the total number of atoms in the universe?