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Okay, I've had enough. I've seen references from innumerable astronomers for the number of stars in our galaxy. They range from 100 to 400 billion.
So who's right?
- Mike Petersen
Thats a really fuzzy number, Mike. These authors claim to have used stellar photometry on NGC 300 and detected a disk of stars that extends to 10 effective radii. While the light from such a disk would be diffuse and hard to detect, it would probably have a significant impact on the estimate of stars in the galaxy.http://arxiv.org/abs/astro-ph/0602573
The paper you reference has more to do with galaxy counts than star counts. Although I see the point you are making, I still wonder about the best estimate today of the number of stars in our own galaxy. A range of 100 to 400 billion is a lot more than "fuzzy". I would think it to be downright embarrassing. I don't even know what to say to kids when they ask how many stars there are in our galaxy. I give them 200 billion, but also say we aren't sure, and that estimates vary from 100 to 400 billion. Very unsatisfying, to say the least.
Funny...I hear 100, 200, and 400 billion, but never 300 billion. I wonder why...
- Mike Petersen
I don't know what to say, Mike. We are at a disadvantage in that we are embedded in the galaxy in question. The only viable method that I can think of is to get rotational velocities of MW stars about the galaxy's center, estimate a total mass using galaxies that we think might be similar, and divide by the mass of an average star. The fact that the authors of the referenced paper found a disk of stars extending to 10x the radius at which stars are visually detectable tells me that our naive reliance on observations of things visible from Earth and Earth orbit may prevent us from making an accurate inventory. For instance, what exists in the intergalactic voids? Is there a lot of molecular Hydrogen or other materials? If it is diffuse and does not emit radiation at a level detectable to us and does not absorb EM from background sources strongly enough for us to detect, we will not be able to detect it, much less quantify it to add to our inventory.
Update - All I hear now is the number 400 billion.
Okay, I can live with that.
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