Stars in the milky way?

Quick question guys. Im constanly reading different estimates for the number of stars in our galaxy. Sometimes i see 100 billion, sometimes i see 3 to 400 billion. Is there an accepted estimate? These different "facts" or estimates differ by hundreds of millions of stars. Cheers

There's no definite answer, it's just a guess - it's a bit like this, you look into a large forest, there could be 100,000 trees - or - there could be a million, the milkyway is just too large to know.....

Keith..

Mickey,

Wikipedia says

The Milky Way is estimated to contain 200 billion,and up to 400 billion, stars (if small-mass stars predominate).

Thats a very large margin of error. If you want a more scientific answer then the vernacular "big shed loads" will suffice.

The simple answer is we don't know.
What is the reason for your question?

The figure always given was 1 billion. The higher figures of 2 to 4 billion seem to be more recent estimates, but I don't know whether this is based on observations or guesswork. The total mass of the galaxy must be reasonably well known, but the breakdown into stars of different masses and dark matter is a different matter.

4 billion would be far too light.

Astronomy Cafe notes the following:

"From a number of studies, the mass of the Milky Way can be estimated to an accuracy of perhaps 20 percent as 140 billion times the mass of the Sun, if you use the Sun's speed around the core of the galaxy. Radio astronomers have detected much more material outside the orbit of the Sun, so the above number is probably an underestimate by a factor of 2 to 5 times in mass alone.

Now, to find out how many stars this represents, you have to divide by the average mass of a star. If you like the sun, then use 'one solar mass' and you then get about 140 billion sun-like stars for what's inside the sun's orbit. But astronomers have known for a long time that stars like the sun in mass are not that common. Far more plentiful are stars with half the mass of the sun, and even one tenth the mass of the sun. The problem is that we don't know exactly how much of the Milky Way is in the form of these low-mass stars. In text books, you will therefore get answers that range anywhere between a few hundred billion and as high as a trillion stars depending on what the author used as a typical mass for the most abundant type of star. This is a pretty embarrasing uncertainty, but then again, why would you need to know this number exactly? "

I recently had a chat with Liam Dumpleton (on Fridat actually), the late Dunsink Director Bill Dumpleton's son, and he recanted a story to me about this kind of subject Mikey. Here's the abridged version.

Bill was giving a tour of Dunsink to a group of blind people, and he was wondering how he would be able to describe astronomy subjects to them if they couldn't see. One person asked what space is like, to which Bill said "Close your eyes, and tell me what you see". Of course, they were all blind, but still responded with "Nothing". "That is exactly what space is like," Bill said.

Then someone asked "How many stars are in the Universe?". Bill replied "Think back to the last time you were on a beach. Imagine picking up a handful of sand, then letting it fall between your fingers into the wind. Each grain is a star. Now add up all those grains of sand on your beach, and on all the beaches in Ireland, double it, and you don't come close".

A neat way to describe to someone the common questions about our Universe, wouldn't you say?

The truth Mikey is that we don't have, nor ever will have, a definite answer. Physics can only help us guestimate the answer based on the evidence given to us.

Seanie.