How many stars in our galaxy if they had the mass of our Sun.

Click For Summary
SUMMARY

The discussion focuses on estimating the mass of the Milky Way Galaxy by treating it as a uniform sphere with the Sun orbiting around its center. The gravitational acceleration formula, \( g = \frac{GM}{r^2} \), and the centripetal acceleration equation, \( a = \frac{v^2}{r} \), are utilized to derive the necessary calculations. The user calculates the centripetal acceleration as \( a = 2.81 \times 10^{-10} \, \text{m/s}^2 \) based on the Sun's orbital radius of \( 2.85 \times 10^{20} \, \text{m} \) and orbital period of \( 200 \, \text{million years} \). The discussion concludes that the mass of the galaxy can be estimated using these derived values.

PREREQUISITES
  • Understanding of gravitational acceleration and its formula, \( g = \frac{GM}{r^2} \)
  • Familiarity with centripetal acceleration and the equation \( a = \frac{v^2}{r} \)
  • Knowledge of orbital mechanics, specifically relating to the Milky Way Galaxy
  • Basic proficiency in unit conversions, particularly between years and seconds
NEXT STEPS
  • Research the calculation of galaxy mass using gravitational dynamics
  • Learn about the distribution of mass in galaxies and its implications on orbital mechanics
  • Explore the concept of stellar density and its relation to the number of stars in a galaxy
  • Investigate the methods used in astrophysics to estimate distances in light years
USEFUL FOR

Astronomy students, astrophysicists, and anyone interested in understanding the mass estimation of galaxies and the dynamics of stellar orbits.

balletgirl
Messages
35
Reaction score
0

Homework Statement



The Sun rotates about the center of the Milky Way Galaxy at a distance of about 3.00x10^4 light years from the center (1ly= 9.50x10^5 m). If it takes about 200 million years to make one rotation, estimate the mass of our galaxy. Assume the mass distribution of our galaxy is concentrated mostly in a central uniform sphere. If all the stars had about the same mass as our Sun, how many stars would there be in our galaxy?


Homework Equations



I have no clue, the most common equation I use is g=GM/r^2 and a=v^2/r.

The Attempt at a Solution



I do not know where to start.
 
Physics news on Phys.org
Treat the galaxy as if it was a planet that the sun was orbiting.
 
Well, g is just gravitational acceleration, and is the a in a=v^2/r... but there's an equation missing.


a=\frac{4 \pi^2 r}{T^2}
 
Okay, so I did T= 200,000,000 yrs = 6.31x10^15 s
& R= 2.85x10^20

a=4pi^2*r/T^2
a= 4(3.14)^2*(2.85x10^20)/(6.31x10^15s)
a=39.4(2.85x10^20)/3.98x10^31
a= 2.81x10^-10

I doubt this is right since it is negative
 
No it's not... the exponent is negative, but the number is positive, just very small. And it should be small...
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
25K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
6K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 2 ·
Replies
2
Views
2K
Replies
4
Views
11K
Replies
1
Views
1K
  • · Replies 6 ·
Replies
6
Views
1K
  • · Replies 9 ·
Replies
9
Views
1K
  • · Replies 5 ·
Replies
5
Views
3K