Celestia Forums

Is there any known data about the spread of stellar ages in our galaxy? (not of evolutionary phase, I mean actual age of the stars in years)

Is there a smooth spread of ages from a few thousand years old to the age of the galaxy (about 13.4 billion years, IIRC? It's only a few hundred million years younger than the universe I think)? Or are most stars clustered around a certain age (e.g. 3-7 billion years?). Or does it vary by neighbourhood?

Obivously the stars to look at would be the G, K, and M Vs since they're around for a long time. But new A and F Vs are being formed all the time or we wouldn't be seeing them today.

It varies.

Ages of individual stars can't be measured except for a few special cases.
See http://www.astro.ucla.edu/~wright/age.html

Ages of individual open and globular clusters can be estimated from their HR diagrams. See http://www.madsci.org/posts/archives/fe ... .As.r.html

Most, but not all, of the globulars orbiting the Milky Way seem to have formed about 12 Gyr ago.

The ages of open clusters vary from currently forming (e.g. the cluster in the Orion Nebula) to about 10GYr. See http://www.aas.org/publications/baas/v2 ... 11008.html

Nuts. Yeah, I knew about that stuff...

Anyone care to at least make an educated guess? Basically, if you just take a random spread of stars in the stellar neighbourhood (within say 100-200 ly) would you just see a random spread of ages across the whole range or would they be mostly in the same age band within a few billion years of eachother?

John Dollan has made a long list of most of the stars within 100 lys which have been catalogued, whith some detail about each;

Out of those stars which have been assigned ages,
there are

46 less than a billion years old,
26 from one billion to 2 billion years old,
18 from two billion to three billion years old,
23 from three billion to four billion years old,
15 from four billion to five billion years old,
14 from five billion to six billion years old,
12 from six billion to seven billion years old,
6 from seven billion to eight billion years old,
11 from eight billion to nine billion years old.
9 from nine billion to ten billion years old,
10 from ten billion years to eleven billion years old,
two stars thirteen billion years old,
and one at 15 billion years (which is older than the universe itself (!))
(shome mishtake shurely!)

But this is a skewed sample, as few of the dimmer stars (which are mostly red dwarfs) have been dated. Red dwarfs are long lived, and so are more likely to be older stars; thiswill probably shift the real distribution until the ages of the stars are fairly evenly distributed, with the oldest stars red and white dwarfs.

I would expect star ages to be skewed towards older ages. The rate of star formation slows down with time as the available interstellar gas depletes.

bdm wrote:I would expect star ages to be skewed towards older ages. The rate of star formation slows down with time as the available interstellar gas depletes.

Erm, not that I've heard. Interstellar gas isn't "depleting", it's being replenished all the time by supernovae.

Malenfant wrote:

bdm wrote:I would expect star ages to be skewed towards older ages. The rate of star formation slows down with time as the available interstellar gas depletes.

Erm, not that I've heard. Interstellar gas isn't "depleting", it's being replenished all the time by supernovae.

Supernovae (and planetary nebulae) do recycle the gases from the stars, but the process isn't 100% efficient. Some of the material from the stars gets incorporated into stellar remnants like white dwarfs and neutron stars, or as heavier elements. Thus, the interstellar gas gets slowly depleted over time. It's probably depleting at a rate that's slow enough for it not to appreciably affect the age profile of stars.

This may change in 5 to 10 billion years. At that time, the Milky Way may merge with the Andromeda galaxy, creating a new elliptical galaxy. If that happens, the gases in both galaxies would collide and result in a burst of star formation. This star formation would be so intense that the resulting supernovae would drive the remaining interstellar gas out of the galaxy. Elliptical galaxies don't have much gas, so mostly consist of aging stars with few or no new stars.