<p>As you say stars composition depend on the composition of the molecular cloud where they were created. You have a <strong>molecular cloud</strong> where many stars are being created at the same time, all with the same composition and age, but some are bigger than others. As time goes the bigger stars will die earlier, adding new heavier materials to the cloud which will lead to a new generation of stars with a bigger <a href="http://en.wikipedia.org/wiki/Metallicity" rel="nofollow"><strong>metalicity</strong></a>.</p>

<p>So the star's composition not only depends on where it was created but also on <a href="http://en.wikipedia.org/wiki/Metallicity#Stellar_populations" rel="nofollow"><strong>how old it is</strong></a>.</p>

<p>The best way this can be checked is by studying the stars within a <strong>star cluster</strong>. You may find <a href="http://www.astro.ex.ac.uk/people/mbate/Cluster/index.html" rel="nofollow">this site</a> interesting.</p>

CC BY-SA 3.0
2014-06-02T11:03:31.550Z
2014-06-02T11:03:31.550Z
Joan.bdm
<p>There have of course been extensive observations of clusters of stars. To all intents and purposes, to the limits of experimental accuracy, it looks like stars that are born in the same <em>open cluster</em> or star-forming region are all born with the same composition. e.g. <a href="http://adsabs.harvard.edu/abs/2014A%26A...567A..55S" rel="nofollow">http://adsabs.harvard.edu/abs/2014A%26A...567A..55S</a> , <a href="http://adsabs.harvard.edu/abs/2002AJ....124.2799W" rel="nofollow">http://adsabs.harvard.edu/abs/2002AJ....124.2799W</a> , <a href="http://adsabs.harvard.edu/abs/2007AJ....133.1161D" rel="nofollow">http://adsabs.harvard.edu/abs/2007AJ....133.1161D</a></p>

<p>There are of course various <em>photospheric</em> abundance anomalies in some stars, but these are normally ascribed to mixing processes or nucleosynthesis within the stars, not their birth composition.</p>

<p>The situation in globular clusters is not so clear cut. Multiple populations distinguished by their chemical compositions have been found. Possibly as a result of ancient mergers. So this does not perhaps represent a violation of Tobler's law since these stars would actually have been born in different environments.</p>

<p>Once stars leave their birth environment then they very quickly become mixed around the Galaxy. A star with a peculiar velocity of only 1km/s will travel a parsec in a million years. Stars born in the same place are probably widely distributed around the galaxy in a billion years or so. Most of the mixing is in azimuth or vertically, rather than Galactocentric radius.</p>

<p>Nevertheless there is a <em>radial</em> dependence (Galactocentric radius) of chemical composition (e.g. <a href="http://adsabs.harvard.edu/abs/2010A%26A...511A..56P" rel="nofollow">http://adsabs.harvard.edu/abs/2010A%26A...511A..56P</a> ). Thus stars with similar Galactocentric radii have similar gross chemical compositions (with some scatter). But then this does violate Tobler's law because it means there is a similarity between objects that are on opposite sides of the Galaxy but with similar distance from the Galactic centre.</p>

CC BY-SA 3.0
2014-12-14T22:33:18.973Z
2014-12-14T22:33:18.973Z
ProfRob
<p>There is a principle in Geography called <strong><a href="http://en.wikipedia.org/wiki/Tobler%27s_first_law_of_geography" rel="noreferrer">Tobler's First Law of Geography</a></strong> which states that "Everything is related to everything else, but near things are more related than distant things."</p>

<p>Does this principle apply to star composition?  Do stars that are closer together have similar compositions than those that are far apart?  I'm guessing that stars that are formed in the same stellar nursery would have similar compositions.  Have studies been done to compare the compositions and proximity of stars?</p>

<star><distances>
Does Tobler's First Law of Geography Apply to Star Composition?
Fezter
# Does Tobler's First Law of Geography Apply to Star Composition?

(Asked by: username_0 on 2014-05-31)

There is a principle in Geography called **[Tobler's First Law of Geography](http://en.wikipedia.org/wiki/Tobler%27s_first_law_of_geography)** which states that "Everything is related to everything else, but near things are more related than distant things."

Does this principle apply to star composition? Do stars that are closer together have similar compositions than those that are far apart? I'm guessing that stars that are formed in the same stellar nursery would have similar compositions. Have studies been done to compare the compositions and proximity of stars?

**Tags:** star, distances

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## 2 answers

### Answer by username_1 on 2014-06-02. Score: 4 | Accepted answer

As you say stars composition depend on the composition of the molecular cloud where they were created. You have a **molecular cloud** where many stars are being created at the same time, all with the same composition and age, but some are bigger than others. As time goes the bigger stars will die earlier, adding new heavier materials to the cloud which will lead to a new generation of stars with a bigger [**metalicity**](http://en.wikipedia.org/wiki/Metallicity).

So the star's composition not only depends on where it was created but also on [**how old it is**](http://en.wikipedia.org/wiki/Metallicity#Stellar_populations).

The best way this can be checked is by studying the stars within a **star cluster**. You may find [this site](http://www.astro.ex.ac.uk/people/mbate/Cluster/index.html) interesting.


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### Answer by username_2 on 2014-12-14. Score: 2

There have of course been extensive observations of clusters of stars. To all intents and purposes, to the limits of experimental accuracy, it looks like stars that are born in the same *open cluster* or star-forming region are all born with the same composition. e.g. <http://adsabs.harvard.edu/abs/2014A%26A...567A..55S> , <http://adsabs.harvard.edu/abs/2002AJ....124.2799W> , <http://adsabs.harvard.edu/abs/2007AJ....133.1161D>

There are of course various *photospheric* abundance anomalies in some stars, but these are normally ascribed to mixing processes or nucleosynthesis within the stars, not their birth composition.

The situation in globular clusters is not so clear cut. Multiple populations distinguished by their chemical compositions have been found. Possibly as a result of ancient mergers. So this does not perhaps represent a violation of Tobler's law since these stars would actually have been born in different environments.

Once stars leave their birth environment then they very quickly become mixed around the Galaxy. A star with a peculiar velocity of only 1km/s will travel a parsec in a million years. Stars born in the same place are probably widely distributed around the galaxy in a billion years or so. Most of the mixing is in azimuth or vertically, rather than Galactocentric radius.

Nevertheless there is a *radial* dependence (Galactocentric radius) of chemical composition (e.g. <http://adsabs.harvard.edu/abs/2010A%26A...511A..56P> ). Thus stars with similar Galactocentric radii have similar gross chemical compositions (with some scatter). But then this does violate Tobler's law because it means there is a similarity between objects that are on opposite sides of the Galaxy but with similar distance from the Galactic centre.


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