View Full Version : Standards and the number of Stars in the Milky Way Galaxy

2015-Oct-11, 03:21 AM
Hello. I would just like to know. Is it possible to come up with an 'accurate' statistical calculation of how many stars there are in the Milky Way?

I have heard of 100 billion..200 billion and even 400 billion stars over the years. Is it possible to come up with a reliable number? If it is..the I think there should be
a 'determination' to find this number..and to make sure it is used by 'everyone'..

Also, maybe and accurate number for the number of Galaxies in the Universe.


2015-Oct-11, 04:20 AM
Wiki says 200 - 400 billion.

Also, maybe and accurate number for the number of Galaxies in the Universe.
Presumably, you mean observable universe.
We're not there yet.

esp. since we still guessing at the size of our own galaxy. :D

2015-Oct-11, 08:54 AM
The problem is that you can't see a lot of them. Many are obscured by dust, so that we see the cloud-like structure of the Milky Way. So you have to guess.

2015-Oct-11, 08:56 AM
And even if you could, how would you enforce it? Are you suggesting criminal penalties for using the wrong number? I don't think you'd find much support for that.

2015-Oct-11, 10:14 AM
Wiki says 200 - 400 billion.

I thought it had been pinned down closer than that, but that is indeed what wikipedia says.

However, it footnotes that figure with three sources. OMG

The first is an archived (the wayback machine) NASA/World Book page (that is no longer live on the site). At the end of the first paragraph, it says "There are about 100 billion stars in the Milky Way."

The second is an article from our own Universe Today, that is trying to answer how many stars are in the Universe. It says "Astronomers estimate that the Milky Way contains up to 400 billion stars of various sizes and brightness."

The third is an article that gives a little more justification for its figures, but it is a pop sci article in the Huffington Post by Stan Odenwald. Stan tends to have flights of fancy. His figure? One trillion.

Asking Google "number of stars in the milky way" returns the 100 billion figure, and references a space.com article. That article goes into some detail, but starts by asking Ask the Astronomer, it ends up with 100-400 billion:

So is there any way to figure out how many stars are for sure? In the end, it comes down to an estimate. In one calculation, the Milky Way has a mass of about 100 billion solar masses, so it is easiest to translate that to 100 billion stars. This accounts for the stars that would be bigger or smaller than our sun, and averages them out. Other mass estimates bring the number up to 400 billion.

The next google links I got were the Universe Today, wikipedia, and Ask An Astronomer, in that order.

One of the next links is to Sky and Telescope (finally!) but it has consistency issues. In the body of the text it says "Our own Milky Way is home to around 300 billion stars, but it’s not representative of galaxies in general." In the caption of the graphic it says "The band of the Milky Way across the night sky. Our Sun is only one of a 100 billion stars in our galaxy."

But there is another NASA page in the mix. However it hedges 100-400 billion, and references space.com, Ask the Astronomer, and Odenwald at the end.

2015-Oct-11, 12:31 PM
One of the complicating factors in getting a count is what do you call the line between star and something less massive than a star. Is an L5 brown dwarf a star? There are a lot of them, but they don't make up a lot of the mass of the galaxy, or its brightness.

Side note: I think the trillion star figure may be a misunderstanding. The mass of the galaxy including all of the dark matter and everything else in the halo is sometimes estimated as 1 to 1.5 trillion solar masses. This number is based on the apparent kinematics of the local group.

2015-Oct-11, 01:39 PM
According to WP's Universe (https://en.wikipedia.org/wiki/Universe) entry:

The observable Universe contains approximately 300 sextillion (31023) stars and more than 100 billion (1011) galaxies.

Jeff Root
2015-Oct-11, 02:56 PM
I've used the figure of "roughly 300 billion" stars in the
Milky Way for so long that I don't remember how long.

But if you made that a standard, I'd immediately change
the figure I use to something else.

-- Jeff, in Minneapolis

2015-Oct-11, 03:20 PM
Side note: I think the trillion star figure may be a misunderstanding.

Almost definitely. Probably should be removed as a reference in the wiki article. It doesn't support the 200-400 billion figure, and the calculation is based on local data that is highly variable. (He uses a local estimate of five red dwarfs for each ordinary star, whereas other estimates put that at two red dwarfs for each--that alone would account for almost all the difference. Nevermind other over-simplifications.)