Problem Set 7A

Spica (a type B main sequence star) has mass 2.1x1031 kg. Find the total mass m that will change to energy when the core fuses from hydrogen to helium.

1.5x10^28

A main sequence star has mass (2.0x10^29) kg. Find the total mass that will change to energy when its core fuses from hydrogen to helium.

1.4x10^26

The luminosity of a star is (1.3x10^26) watt. How much mass does the star turn into energy each second?

1.4x10^9

Find the lifetime of Spica in the way the lifetime of the Sun was found in the notes: Use the answers to the last two problems for the total mass Spica will change to energy and for the mass Spica changes to energy each second.

2.8x10^14

The mass of a main-sequence star is 10 times the mass of the Sun. Its luminosity is 3,000 times the luminosity of the Sun.

3.5x10^7

Barnard's star is a nearby main sequence star. Its mass is 0.15 times the mass of the Sun, and its luminosity is 3.5x10-3 times the luminosity of the Sun. Find its lifetime in years, using the final formula in the Lifetime notes.

4.3x10^11

The luminosity of Spica is 12,000 times the luminosity of the Sun, or 4.8x1030 watt. How much mass does Spica turn into energy each second?

5.3x10^13

Now it's time to find the lifetime using the simpler formula based on the lifetime of the Sun: Spica's mass is 10.5 times the mass of the Sun Its luminosity is 12,000 times the luminosity of the Sun. Find its lifetime in years, using the final formula in the Lifetime notes.

8.8x10^6

You should have found for Spica a lifetime of about 2.8x1014 seconds. What is its lifetime in years?

8.9x10^6