<p>There isn't really a database as you request. Finding the ages of stars is difficult. Only one star has an accurately known age - the Sun. That comes from radioisotope dating of meteorites. For other stars we must rely on models to a greater or lesser extent and we can only estimate an age if the star has a mass or is in a phase of its evolution where things are changing rapidly enough to give some handle on how old it is. For stars at the mass of the Sun or a little bit bigger, one can use evolution in the Hertzsprung-Russell diagram. Stars become more luminous as they burn through their core hydrogen and precise measurements can give an age to about <span class="math-container">$\pm 1$</span> Gyr. These are the data that <a href="https://arxiv.org/abs/1410.3829" rel="nofollow noreferrer">Snaith et al. (2015)</a> use in their paper.</p>

<p>So what Snaith et al. do is they attempt to constrain the star formation history of our Galaxy (or at least stars in the disk of our Galaxy) by making a Galactic Chemical Evolution model that predicts how the abundances of silicon and iron change with time and compare the results of their model with the observed silicon and iron abundances in this set of solar-type stars with reasonably well-estimated ages. Iron and silicon are used because they provide differing constraints. Iron is produced during the evolution of relatively low-mass (<span class="math-container">$1.5 - 4 M_{\odot}$</span>) stars that live their long(ish) lives (1-10 Gyr), become white dwarfs and then some of the white dwarfs explode as type Ia supernovae. Silicon is produced by massive stars with short lives (<span class="math-container">$&lt;0.1$</span> Gyr) and spread promptly into the interstellar medium by core-collape type II supernovae.</p>

<p>A representative lot from Snaith's paper is shown below. The star forming rate is shown in plot (a) and the match of the model to the observational data (they are trying to match the solid green points here) on chemical abundance is shown in the other plots.</p>

<p><a href="https://i.sstatic.net/NAAce.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/NAAce.png" alt="Snaith et al. plot"></a></p>

<p>They test a number of models and different assumptions, but it appears to be quite a robust result (found in other studies also) that there was a burst of star formation 10-12 billion years ago, a lull at 8-9 billion years ago and then a more constant, lower rate over the last 7 billion years. The very low rate in their model over the last 2 billion years is unlikely to be true and is probably an artefact of the age uncertainties in their data points (e.g. stars with age of <span class="math-container">$1 \pm 1$</span> billion years) and we certainly see plenty of star formation in the disk of the Galaxy today.</p>

<p><strong>Contrary to what you say in your question</strong> this <strong>does</strong> (almost) represent the age distribution of stars in the Galaxy. That is because the vast majority of stars (90+%) are of a solar mass or lower. Such stars have main sequence life times of 11+ billion years, such that almost every one of them that was born is still a main sequence star now.</p>

<p>There will be a small reduction in the numbers of the oldest stars, because a small fraction of those (<span class="math-container">$&lt;10$</span>%) will have lived and died and also because a small fraction of the oldest stars may have escaped the Galaxy entirely (due to various kinematic processes that cause their orbital speeds to change). There is also an effect whereby if you take a volume close to the Sun, the oldest stars will be under-represented because they are distributed more broadly around the disc midplane for the same reason.</p>

<p>But by an large, the upper left plot in the picture is roughly what we expect the age distribution of stars to be in the Galactic disk.</p>

<p>There are a small population of very old stars (<span class="math-container">$12+$</span> bilion years), perhaps 1%, that are distributed more widely in the Galactic halo.</p>

CC BY-SA 4.0
2020-03-21T10:41:42.350Z
2020-03-21T10:52:33.643Z
2020-03-21T10:52:33.643Z
ProfRob
<p>I don't know about stars in general, but for giant stars, <a href="https://www.researchgate.net/publication/333444811_Life_in_the_fast_lane_a_direct_view_of_the_dynamics_formation_and_evolution_of_the_Milky_Way&#39;s_bar" rel="nofollow noreferrer">the following histogram</a> shows the age distribution of those in our Galaxy based on their location in the Galaxy. </p>

<p><a href="https://i.sstatic.net/chi3f.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/chi3f.png" alt="enter image description here"></a></p>

<p>This means that most stars are between 7 and 8 billion years old. </p>

CC BY-SA 4.0
2020-02-20T11:26:12.233Z
No, it doesn't. It *might* mean that most giants are 7-8 Gyr, but given they have to have lived lives as main sequence stars, that is hardly surprising. Then of course they die, so there might be a shortage of old ones. In short, you can tell very little about the typical ages of stars without knowing much more about stellar evolution, the mass distribution of the sample and the selection effects in its construction.
ProfRob
CC BY-SA 4.0
2020-02-20T09:39:57.203Z
2020-02-20T09:39:57.203Z
usernumber
<p>There are several ways of determining the age of a star: its position in the HR diagram, the presence of a protoplanetary disk, it belonging to a cluster...</p>

<p>When did the stars in our Galaxy form? Do we know their age? Does there exists a database of stars for which we know the age, from which this average could be computed ? Is there a histogram of how long ago the stars in our Galaxy formed?</p>

<hr>

<p>The amount of stars being formed as a function of time is shown for instance in <a href="https://arxiv.org/abs/1410.3829" rel="nofollow noreferrer">Snaith et al 2014</a>, but this doesn't directly translate into a histogram of the age of the stars currently in our galaxy, since the more massive ones that formed early on are gone. </p>

CC BY-SA 4.0
2020-01-13T13:25:09.237Z
@Alchimista "What is the average age of stars in the MW?" is in principle more easily answered than "When did the MW form?", since the former can be computed from a suitable database of stellar age estimates, while the latter has to deal with questions of assembly and mergers.
Peter Erwin
CC BY-SA 4.0
2020-01-14T07:52:18.223Z
@Peter Erwin no doubt. I am not saying that it is hard to answer if faced to a table. I am saying that is meaningless as if we would calculate the average age of butterflies and humans. At least I don't see any meaningful use I could do of such a number. Nice that butterflies came to mind because there is even a resemblance to stars. What would be the age of a butterfly? Do its various stages count?
Alchimista
CC BY-SA 4.0
2020-01-15T07:31:44.997Z
@Alchimista 1. The question was about the ages of stars, not the age of the Milky Way. 2. If you wanted to know the average of terrestrial animals, then you would include the ages of humans and butterflies (and other animals) in your calculation. ("Is the average age of animals more or less than that of plants?" is a perfectly sensible question.)
Peter Erwin
CC BY-SA 4.0
2020-01-15T08:13:13.557Z
@usernumber I would say yes. The paragraph you have add makes the question somewhat different. Though the majority of stars in MW are small red stars. Again I am not really sure one can discern between two red dwarf, one being formed, say, 1 billion years after the other.
Alchimista
CC BY-SA 4.0
2020-01-15T08:19:58.783Z
@Peter Erwin funny because it is exactly my point. It translates in the age of the galaxy to be compared to others. If not so intended, it translates in something like comparing the average age of different types of stars, which is not the *original* question.
Alchimista
CC BY-SA 4.0
2020-01-15T12:19:36.737Z
@Alchimista: There was no single point at which our galaxy formed, as this is a complex process of hierarchical assembly. Additionally, star formation rates are continuous and peaked in our (as many other galaxies) around $z=2$, producing an IMF of which the most massive stars are long gone. On top of that, galaxies continue to accrete extragalactic gas from which new star-forming regions arise. OP's questions has therefore full validity, and your suggestion is oversimplified.
AtmosphericPrisonEscape
CC BY-SA 4.0
2020-01-15T23:52:44.087Z
[Has the Milky Way formed stars in bursts?](https://www.newscientist.com/article/mg13017644-300-science-has-the-milky-way-formed-stars-in-bursts/) , [Age distribution of giant stars](https://www.researchgate.net/figure/Age-distribution-of-giant-stars-in-the-bar-compared-to-that-of-inner-Galaxy-stars-outside_fig1_333444811).
Keith McClary
CC BY-SA 4.0
2020-01-16T07:05:21.290Z
Seems that my comments are cryptic to other commenters. I am not saying that galaxy formed in a moment! I am saying that an average age of stars cannot be even be defined if not as a mere numerical exercises and right because you might observe a blu supergiant g now went - side a still shining red dwarf. What would be the meaning of an averaged thing that never existed? The comment of @AtmosphericPrisonEscape just put some facts that rather than negate the validity of my comment do the opposite.
Alchimista
CC BY-SA 4.0
2020-01-16T07:24:34.983Z
Should means something. https://www.google.com/search?q=average+age+of+stars+in+the+milky+way&oq=average+age+of+stars+in+the+milky+way+&aqs=chrome..69i57.14119j0j7&client=ms-android-xiaomi-rev1&sourceid=chrome-mobile&ie=UTF-8#ip=1 nothing straight comes up if not in my interpretation.
Alchimista
CC BY-SA 4.0
2020-02-20T11:31:02.123Z
It's a good question, but unfortunately, the answer is no. Estimating the ages of typical main sequences stars (which are M dwarfs) is very hard. Even estimating the age of solar type main sequence stars is nearly as hard. There are estimates of age distributions, but not really a database of ages for typical stars. The answer also depends greatly on where in the Galaxy you are considering - the bulge is old, the disk is younger, the halo is very old.
ProfRob
CC BY-SA 4.0
2020-01-08T09:30:14.187Z
Why not to ask for when our galaxy formed? It seems a more sensible question, at least to start.
Alchimista
CC BY-SA 4.0
2020-01-08T09:43:41.097Z
@Alchimista Feel free to ask that question! I fail to see what makes it more sensible, though.
usernumber
CC BY-SA 4.0
2020-01-08T10:14:09.570Z
Because it assume somewhat a model or a discussion. Otherwise star can be regarded as individual or within individual star forming clouds and an average age won't tell much, takes alone.
Alchimista
CC BY-SA 4.0
2020-01-08T10:58:58.640Z
@Alchimista but that will only indicate the maximal age of stars in the galaxy. Unless all the stars formed at the same time, it doesn't answer my question.
usernumber
CC BY-SA 4.0
2020-01-08T13:19:56.007Z
I am not going to argue but it is indeed what I wanted to suggest. You can average the age of lions and trees as both being living orgsnisms, sure. But what can you meaningfully extract out of it?
Alchimista
CC BY-SA 4.0
2020-01-08T13:24:42.777Z
Otherwise things can get sense if a context is given. An example might be https://arxiv.org/abs/1410.3829
Alchimista
<star><age><hr-diagram>
Is there a stellar database that indicates how long ago stars in our Galaxy formed?
usernumber
# Is there a stellar database that indicates how long ago stars in our Galaxy formed?

(Asked by: username_0 on 2020-01-08)

There are several ways of determining the age of a star: its position in the HR diagram, the presence of a protoplanetary disk, it belonging to a cluster...

When did the stars in our Galaxy form? Do we know their age? Does there exists a database of stars for which we know the age, from which this average could be computed ? Is there a histogram of how long ago the stars in our Galaxy formed?

---

The amount of stars being formed as a function of time is shown for instance in [Snaith et al 2014](https://arxiv.org/abs/1410.3829), but this doesn't directly translate into a histogram of the age of the stars currently in our galaxy, since the more massive ones that formed early on are gone.

**Tags:** star, age, hr-diagram
> **Comments:**
> **username_2**: Why not to ask for when our galaxy formed? It seems a more sensible question, at least to start.  
> **username_0**: @Alchimista Feel free to ask that question! I fail to see what makes it more sensible, though.  
> **username_2**: Because it assume somewhat a model or a discussion. Otherwise star can be regarded as individual or within individual star forming clouds and an average age won't tell much, takes alone.  
> **username_0**: @Alchimista but that will only indicate the maximal age of stars in the galaxy. Unless all the stars formed at the same time, it doesn't answer my question.  
> **username_2**: I am not going to argue but it is indeed what I wanted to suggest. You can average the age of lions and trees as both being living orgsnisms, sure. But what can you meaningfully extract out of it?  
> **username_2**: Otherwise things can get sense if a context is given. An example might be https://arxiv.org/abs/1410.3829  
> **username_1**: @Alchimista "What is the average age of stars in the MW?" is in principle more easily answered than "When did the MW form?", since the former can be computed from a suitable database of stellar age estimates, while the latter has to deal with questions of assembly and mergers.  
> **username_2**: @Peter Erwin no doubt. I am not saying that it is hard to answer if faced to a table. I am saying that is meaningless as if we would calculate the average age of butterflies and humans. At least I don't see any meaningful use I could do of such a number. Nice that butterflies came to mind because there is even a resemblance to stars. What would be the age of a butterfly? Do its various stages count?  
> **username_1**: @Alchimista 1. The question was about the ages of stars, not the age of the Milky Way. 2. If you wanted to know the average of terrestrial animals, then you would include the ages of humans and butterflies (and other animals) in your calculation. ("Is the average age of animals more or less than that of plants?" is a perfectly sensible question.)  
> **username_2**: @usernumber I would say yes. The paragraph you have add makes the question somewhat different. Though the majority of stars in MW are small red stars. Again I am not really sure one can discern between two red dwarf, one being formed, say, 1 billion years after the other.  
> **username_2**: @Peter Erwin funny because it is exactly my point. It translates in the age of the galaxy to be compared to others. If not so intended, it translates in something like comparing the average age of different types of stars, which is not the *original* question.  
> **username_3**: @Alchimista: There was no single point at which our galaxy formed, as this is a complex process of hierarchical assembly. Additionally, star formation rates are continuous and peaked in our (as many other galaxies) around $z=2$, producing an IMF of which the most massive stars are long gone. On top of that, galaxies continue to accrete extragalactic gas from which new star-forming regions arise. OP's questions has therefore full validity, and your suggestion is oversimplified.  
> **username_4**: [Has the Milky Way formed stars in bursts?](https://www.newscientist.com/article/mg13017644-300-science-has-the-milky-way-formed-stars-in-bursts/) , [Age distribution of giant stars](https://www.researchgate.net/figure/Age-distribution-of-giant-stars-in-the-bar-compared-to-that-of-inner-Galaxy-stars-outside_fig1_333444811).  
> **username_2**: Seems that my comments are cryptic to other commenters. I am not saying that galaxy formed in a moment! I am saying that an average age of stars cannot be even be defined if not as a mere numerical exercises and right because you might observe a blu supergiant g now went - side a still shining red dwarf. What would be the meaning of an averaged thing that never existed? The comment of @AtmosphericPrisonEscape just put some facts that rather than negate the validity of my comment do the opposite.  
> **username_2**: Should means something. https://www.google.com/search?q=average+age+of+stars+in+the+milky+way&oq=average+age+of+stars+in+the+milky+way+&aqs=chrome..69i57.14119j0j7&client=ms-android-xiaomi-rev1&sourceid=chrome-mobile&ie=UTF-8#ip=1 nothing straight comes up if not in my interpretation.  
> **username_5**: It's a good question, but unfortunately, the answer is no. Estimating the ages of typical main sequences stars (which are M dwarfs) is very hard. Even estimating the age of solar type main sequence stars is nearly as hard. There are estimates of age distributions, but not really a database of ages for typical stars. The answer also depends greatly on where in the Galaxy you are considering - the bulge is old, the disk is younger, the halo is very old.  

---

## 2 answers

### Answer by username_5 on 2020-03-21. Score: 3 | Accepted answer

There isn't really a database as you request. Finding the ages of stars is difficult. Only one star has an accurately known age - the Sun. That comes from radioisotope dating of meteorites. For other stars we must rely on models to a greater or lesser extent and we can only estimate an age if the star has a mass or is in a phase of its evolution where things are changing rapidly enough to give some handle on how old it is. For stars at the mass of the Sun or a little bit bigger, one can use evolution in the Hertzsprung-Russell diagram. Stars become more luminous as they burn through their core hydrogen and precise measurements can give an age to about $\pm 1$ Gyr. These are the data that [Snaith et al. (2015)](https://arxiv.org/abs/1410.3829) use in their paper.

So what Snaith et al. do is they attempt to constrain the star formation history of our Galaxy (or at least stars in the disk of our Galaxy) by making a Galactic Chemical Evolution model that predicts how the abundances of silicon and iron change with time and compare the results of their model with the observed silicon and iron abundances in this set of solar-type stars with reasonably well-estimated ages. Iron and silicon are used because they provide differing constraints. Iron is produced during the evolution of relatively low-mass ($1.5 - 4 M\_{\odot}$) stars that live their long(ish) lives (1-10 Gyr), become white dwarfs and then some of the white dwarfs explode as type Ia supernovae. Silicon is produced by massive stars with short lives ($<0.1$ Gyr) and spread promptly into the interstellar medium by core-collape type II supernovae.

A representative lot from Snaith's paper is shown below. The star forming rate is shown in plot (a) and the match of the model to the observational data (they are trying to match the solid green points here) on chemical abundance is shown in the other plots.

[![Snaith et al. plot](https://i.sstatic.net/NAAce.png)](https://i.sstatic.net/NAAce.png)

They test a number of models and different assumptions, but it appears to be quite a robust result (found in other studies also) that there was a burst of star formation 10-12 billion years ago, a lull at 8-9 billion years ago and then a more constant, lower rate over the last 7 billion years. The very low rate in their model over the last 2 billion years is unlikely to be true and is probably an artefact of the age uncertainties in their data points (e.g. stars with age of $1 \pm 1$ billion years) and we certainly see plenty of star formation in the disk of the Galaxy today.

**Contrary to what you say in your question** this **does** (almost) represent the age distribution of stars in the Galaxy. That is because the vast majority of stars (90+%) are of a solar mass or lower. Such stars have main sequence life times of 11+ billion years, such that almost every one of them that was born is still a main sequence star now.

There will be a small reduction in the numbers of the oldest stars, because a small fraction of those ($<10$%) will have lived and died and also because a small fraction of the oldest stars may have escaped the Galaxy entirely (due to various kinematic processes that cause their orbital speeds to change). There is also an effect whereby if you take a volume close to the Sun, the oldest stars will be under-represented because they are distributed more broadly around the disc midplane for the same reason.

But by an large, the upper left plot in the picture is roughly what we expect the age distribution of stars to be in the Galactic disk.

There are a small population of very old stars ($12+$ bilion years), perhaps 1%, that are distributed more widely in the Galactic halo.


---

### Answer by username_0 on 2020-02-20. Score: -2

I don't know about stars in general, but for giant stars, [the following histogram](https://www.researchgate.net/publication/333444811_Life_in_the_fast_lane_a_direct_view_of_the_dynamics_formation_and_evolution_of_the_Milky_Way's_bar) shows the age distribution of those in our Galaxy based on their location in the Galaxy.

[![enter image description here](https://i.sstatic.net/chi3f.png)](https://i.sstatic.net/chi3f.png)

This means that most stars are between 7 and 8 billion years old.

> **Comments:**
> **username_5**: No, it doesn't. It *might* mean that most giants are 7-8 Gyr, but given they have to have lived lives as main sequence stars, that is hardly surprising. Then of course they die, so there might be a shortage of old ones. In short, you can tell very little about the typical ages of stars without knowing much more about stellar evolution, the mass distribution of the sample and the selection effects in its construction.  

---

