Estimate the probability that our Sun would collide with another star in the Andromeda Galaxy, if a collision between the Milky Way and the Andromeda Galaxy were happening at the present time.
To simplify the problem, assume that each galaxy has 100 billion stars exactly like the Sun spread evenly over a circular disk with a radius of 100,000 light-years
Estimate the probability that a particular gas cloud in our galaxy would collide with another gas cloud in the Andromeda Galaxy. To simplify the problem, assume that each galaxy contains 100,000 clouds of warm hydrogen gas, that each cloud has a radius of 300 light-years, and that these clouds are spread evenly over a circular disk with a radius of 100,000 light-years.
Compare the probabilities you found in parts a) and b) and use them to explain what you see in Figure 21.5 in the textbook