# Gravitation problem (estimate numbers of stars in our galaxy)

• U.Renko
In summary, the sun's mass and orbital period around the center of the Milky Way can be used to estimate the total mass of the galaxy. Assuming a spherically symmetric distribution and that all stars have the same mass as the sun, we can estimate the number of stars in our galaxy by dividing the total mass of the galaxy by the mass of the sun.
U.Renko

## Homework Statement

The sun mass MS = 2.0 E30 kg revolves around the center of the milky way which has a total extension of 2.2 E20 m. The sun takes 2.5 E8 years to complete one revolution. Estimate the number of star in our galaxy based on this data.

Suppose that the distribution is spherically simetric and the sun is in the very outskirts of the galaxy.

## Homework Equations

$F = \frac{-GmM}{r^2}$

## The Attempt at a Solution

I'm not sure where to start.
What I did think is use the mass of the galaxy somehow (which I found as result in another exercise, but could be done by Kepler's third law, since we have the period and the distance to center.) MG = 1.5 E12 times the mass of sun = 3 E42 kg.

I feel that I have to integrate something, but how could that give me a discrete number of stars...

Hi U.Renko!
U.Renko said:
The sun mass MS = 2.0 E30 kg revolves around the center of the milky way which has a total extension of 2.2 E20 m. The sun takes 2.5 E8 years to complete one revolution. Estimate the number of star in our galaxy based on this data.

Suppose that the distribution is spherically simetric and the sun is in the very outskirts of the galaxy.

I feel that I have to integrate something, but how could that give me a discrete number of stars...

I'll guess that you're supposed to assume that all stars have the same mass as the sun.

## 1. How do scientists estimate the number of stars in our galaxy?

Scientists use a variety of methods to estimate the number of stars in our galaxy. One common method is to measure the brightness of a small sample of stars and then extrapolate that data to estimate the total number of stars in the galaxy. Another method is to use computer simulations to model the distribution of stars in the galaxy.

## 2. What is the estimated number of stars in our galaxy?

The estimated number of stars in our galaxy, the Milky Way, is approximately 200-400 billion. However, this number is constantly changing as new data and research are being conducted.

## 3. How accurate is our current estimate of the number of stars in our galaxy?

Our current estimate of the number of stars in our galaxy is considered to be fairly accurate, but not exact. This is because there are still many unknowns about the structure and distribution of stars in the Milky Way. Additionally, the estimate may also change as new technologies and methods for observation and measurement are developed.

## 4. Is it possible to count every single star in our galaxy?

It is not possible to count every single star in our galaxy. This is because our galaxy is so vast and complex, and there are many regions that are difficult to observe or measure. Additionally, new stars are constantly being formed and old stars are dying, making it difficult to keep track of every single star at any given time.

## 5. How does the estimated number of stars in our galaxy compare to other galaxies?

The estimated number of stars in our galaxy is similar to the estimated number of stars in other spiral galaxies of similar size and mass. However, larger galaxies such as elliptical galaxies can have significantly more stars, while smaller galaxies may have fewer stars.

• Science Fiction and Fantasy Media
Replies
13
Views
2K
• Introductory Physics Homework Help
Replies
4
Views
24K
• Introductory Physics Homework Help
Replies
1
Views
1K
• Introductory Physics Homework Help
Replies
5
Views
5K
• Introductory Physics Homework Help
Replies
4
Views
3K
• Astronomy and Astrophysics
Replies
4
Views
2K
• Introductory Physics Homework Help
Replies
4
Views
7K
• Introductory Physics Homework Help
Replies
4
Views
11K
• Cosmology
Replies
4
Views
1K
• Introductory Physics Homework Help
Replies
2
Views
2K