Counting Stars

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xmo1

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from comments like this: The galaxy contains 200 billion stars. The galaxy contains 300 billion stars.<br /><br />Is there a formula for counting stars, not that I want to know it, but where do numbers like this originate? <div class="Discussion_UserSignature"> <p>DenniSys.com</p> </div>
 
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harmonicaman

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Well, the whole issue of "How many stars are in the Galaxy (and the Universe)" was recently thrown into flux because it was discovered that regions of the Milky Way containing hot glowing gasses are illuminated not by the gases themselves, but by imbedded stars within the gas clouds which are responsible for the illumination.<br /><br />These uncounted stars probably raise the Milky Way's star count by over one billion!<br /><br />There is no clear consensus as to the total number of stars in the Milky Way galaxy and the estimates vary widely.<br /><br />Related link.
 
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qso1

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The main reason for the estimates of stars being so wide is the amount that can be put in a volume the size and shape of a galaxy like the milky way. And the fact that the concentration of stars increases the closer to the galactic center one gets. We will probably never know how many stars actually are in the milky way galaxy. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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xmo1

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The 300 billion was an estimate for Andromeda actually.<br /><br />I was wondering how the numbers are acquired or calculated. Seems a computer program could detect and count points of light in a high resolution digital photograph from HST, and produce a histogram or some other type of calculated results. So there are probably enough resources and data available for those who like to do statistical estimates. <div class="Discussion_UserSignature"> <p>DenniSys.com</p> </div>
 
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qso1

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I've heard 200 to 400 billion for the milkyway. Even hubble would have a tough time identifying stars as point sources in a galaxy at Andromedas distance. The brighter stars may be seen as point sources but more often than not, the points of lights seen at Andromedas distance are collections of stars a few Ly apart. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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thalion

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IIRC, the method often used for estimating the number of stars in the Milky Way is the simplest: taking the mass of the Galaxy in solar masses and dividing that by some reasonable mass figure. If the Galaxy has a mass of 100 billion solar masses, then if you divide that by one solar mass, you get 100 billion stars. However, we all know that the "average star" in the Galaxy is *not* the size of the Sun, so as the figure goes down, the number of potential stars goes up. Half a solar mass, 200 billion, etc.<br /><br />As Harmonicaman said, we really don't know how many stars are in our Galaxy, only that there are probably over 100 billion of them. This is because we don't know the average mass of a galactic star, nor how much of the Galaxy's mass is actually tied up in stars versus just as gas or dark matter. Finally, including brown dwarfs in the final estimate may greatly increase the answer, even though they aren't technically stars.
 
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xmo1

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Great answ3r. Got the picture. Given data from several devices, such as x-ray and radio telescopes, the project might be fairly interesting. <div class="Discussion_UserSignature"> <p>DenniSys.com</p> </div>
 
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