If the sun's mass is about average, how many stars are there in the Milky Way galaxy?
(This is all the information given in the question and I don't know where to go from here).
4 answers
The mass of the Sun is of the order of 1030
But what do I do from there to get to the number of stars?
unless you have some idea of the mass of the galaxy, you are stuck.
Once you have that, just divide by the sun's mass to see how many "suns" there are in the galaxy.
Once you have that, just divide by the sun's mass to see how many "suns" there are in the galaxy.
You get the mass of the galaxy this way:
It takes about 200 million years for one rotation around the middle of the galaxy, with the Sun about 30,000 light years (convert that to meters). Next, assume nearly all the galaxy mass is in an approximate spherical distribution about the center. Now you have a rotating model, with a period, and a radius... and you have from Newton,
mass= (4pi^2*r^3)/(G&T^2)
gravitational force=centripetal force
GM*Ms/r^2 =Ms(2PI*r /T)^2 /r
leading to
mass= (4pi^2*r^3)/(G*T^2)
a. convert the period to seconds.
b. use radius in meters (from light years)
c. calculate.
Then divide by the Mass of an average star, the sun, and you get the number of stars. It ought to come out pretty close to 175 billion.
It takes about 200 million years for one rotation around the middle of the galaxy, with the Sun about 30,000 light years (convert that to meters). Next, assume nearly all the galaxy mass is in an approximate spherical distribution about the center. Now you have a rotating model, with a period, and a radius... and you have from Newton,
mass= (4pi^2*r^3)/(G&T^2)
gravitational force=centripetal force
GM*Ms/r^2 =Ms(2PI*r /T)^2 /r
leading to
mass= (4pi^2*r^3)/(G*T^2)
a. convert the period to seconds.
b. use radius in meters (from light years)
c. calculate.
Then divide by the Mass of an average star, the sun, and you get the number of stars. It ought to come out pretty close to 175 billion.
1 answer