# Estimating Milky Way Absolute Magnitude

• tristan3214
In summary, the problem involves finding the absolute magnitude of the Milky Way, given the number of stars and their solar luminosity in the B band. The approach of finding the luminosity of one star and multiplying it by the number of stars may be a viable solution, but it may also be possible to use bolometric magnitudes to compare the luminosity to that of the sun. The fact that the problem mentions "solar luminosity" suggests that the stars in question are similar to the sun, making the use of bolometric magnitudes a valid approach. However, the given information may not be enough to easily find the flux or luminosity of the sun in the B band.
tristan3214
Important: All Logs are base 10 and not the natural log.

## Homework Statement

This question is from Foundations of Astrophysics from chapter 19

Suppose the Milky Way consisted of 2.7x10^11 stars, each of solar luminosity MB=4.7. What would be the absolute magnitude of the whole galaxy?

To clarify that is absolute magnitude in the B band rather than the V band.

## Homework Equations

Some equations I have been using:
M=m-5Log(d)+5 Distance Modulus
m2-m1=2.5Log(Flux1/Flux2) for finding flux
F=L/(4∏d^2) for finding luminosity
n=number density=#of stars/volume of cylinder for the galaxy.
average distance=1/n1/3, this is for a sphere though so it is very hand wavy
Mbol=Mbol,sun-2.5Log[L/Lsun]

## The Attempt at a Solution

So when I first saw this problem I wanted to go from absolute magnitude of one star and find the luminosity. With that I would find the total luminosity of the galaxy by multiplying by the number of stars then find absolute magnitude of the galaxy from there.

The ideal way would be to use bolometric magnitudes to get luminosity comparatively to the sun. However, my biggest problem here is that I have absolute magnitude of the stars in B band making things harder. As well as with going a bolometric route there is a lot of looking up of values that aren't easy to find.

I tried finding apparent magnitude of the star by using the average distance between the stars but when I try to find the flux of one of the stars to find the luminosity I don't have the flux of the sun in the B band.

Overall I come here because I feel like maybe there is an easier way than having to search around for things like the luminosity or flux of the sun in the B band.

Last edited:
They tell you "solar luminosity" in the problem, implying L=3.84e26W. I take the fact that they give you the absolute magnitude in the B-band as unnecessary information. But it's a reinforcement that they're truly talking of "sun-like" stars. Then you can just find bolometric magnitude.

## 1. What is the Milky Way Absolute Magnitude?

The Milky Way Absolute Magnitude is a measure of the total amount of light that is emitted by the Milky Way galaxy. It takes into account all of the stars, gas, and dust that make up the galaxy.

## 2. How is the Milky Way Absolute Magnitude estimated?

The Milky Way Absolute Magnitude is estimated by measuring the apparent magnitude of the galaxy and correcting for its distance from Earth. This allows us to calculate the total amount of light emitted by the galaxy, regardless of its distance.

## 3. Why is it important to estimate the Milky Way Absolute Magnitude?

Estimating the Milky Way Absolute Magnitude allows us to understand the overall brightness and size of our home galaxy. It also helps us compare the Milky Way to other galaxies and study its evolution over time.

## 4. What is the current estimated value for the Milky Way Absolute Magnitude?

The current estimated value for the Milky Way Absolute Magnitude is around -20.9. However, this value is constantly being refined as new data and observations become available.

## 5. How does estimating the Milky Way Absolute Magnitude contribute to our understanding of the universe?

By accurately estimating the Milky Way Absolute Magnitude, we can better understand the role of our galaxy in the larger universe. It also allows us to study the relationship between the Milky Way and other galaxies, providing insights into the structure and evolution of the universe as a whole.

Replies
1
Views
1K
Replies
5
Views
4K
Replies
1
Views
3K
Replies
4
Views
2K
Replies
6
Views
1K
Replies
1
Views
1K
Replies
1
Views
1K
Replies
2
Views
2K
Replies
6
Views
2K
Replies
14
Views
2K