Question

1. Given the Sun's lifetime is about 10 billion years, estimate the lifetime of stars with (a)0.2-solar mass, (-5 x 10yr) (b) 3.0 solar mass, (4 x 10 yr) (c)10.0-solar mass x 10 yr) 2. A star is lying 20 pc from the Sun. The star's position on the sky is observed to move 5 arc sec per year relative to background stars. What is the star's transverse (perpendicular to the line of sight) velocity? If the observed red-shift is 0.001 percent (-Δλ/A), calculate the magnitude of the space velocity in m/s. (Take 1 pc 3 ly - 3x 10 m) (3.4 x 10 m/s) 3. A supernova's energy is often compared to the total energy output of the Sun over its lifetime (101 years). Assuming a constant luminosity of 4x 10 W, calculate the total energy output of the Sun. Compare this with the total energy ofa supernova emitted within months (about 1013 Joules). (-10H 10 26

Answer 1

a) Life time of star = -solar mass/solar luminosity times 10^sunlifetime life time of star = -0.2/0.0004 times 10^10 life time of star = -5.0 times 10^12 years b) life time of star = -3.0/75 times 1^10 years life time of star = -4 times 10^8 years c) life time of star = -10/10000 times 10^10 life time of star = -1 times 10^7 years luminosity = 4 times 10^26 w time = 10^10 yr = 10^10 times 365 times 24 times 60 times 60 sec so energy = luminosity times time energy = 4 times 10^26 w times 10^10 times 365 times 24 times 60 times 60 sec energy = 1.26 times 10^44 J energy of sun ~ 10^44 J comparing the sun output energy in its lifetime is 10 times super nova energy emitted in a month