<p>Your intuition is largely correct: the key is that the proto-bulge region had a deep enough potential well so that the supernovas couldn't expel the remaining gas, and so new stars could form out of the gas (enriched by the supernova ejecta) in a continuing cycle. In the low-mass, isolated protogalactic clouds which probably contributed to the halo, the initial round of supernovas ejected most of the gas (including the original gas that hadn't yet formed stars) -- thus, little opportunity to form more stars (out of higher-metallicity gas) on a continuing basis.</p>

<p>It's really the total mass in a given region that matters. For example, the density of stars in the central regions of a globular cluster is pretty high, but the mass of the cluster as a whole isn't enough to keep most of the gas when its massive stars go supernova.</p>

<p>(Side note: the traditional terms "Population I" and "Population II" aren't used all that much any more, since age and metallicity can vary continuously and aren't always strongly associated.)</p>

CC BY-SA 3.0
2016-05-08T13:53:38.590Z
That makes perfect sense. Are there any articles or readings that you know of that I could read for further understanding?
NotSoSN
CC BY-SA 3.0
2016-05-08T12:57:26.470Z
2016-05-08T12:57:26.470Z
Peter Erwin
<p>From what I understand of current models, the bulge of the galaxy formed first, and thus, would contain older population II like stars. Currently, however, the halo has a higher population of stars with lower metalicity than the bulge. Is this because the density  of stars in the bulge is much higher? My thinking is that this is a densely populated region of massive hot stars that die quickly and create a newer region of next generation population I stars that are metal rich. The inverse would be true for the halo where stars are less densely packed. Is this correct?</p>

<star><stellar-evolution><metallicity>
Metalicity and age of bulge stars vs halo
NotSoSN
# Metalicity and age of bulge stars vs halo

(Asked by: username_0 on 2016-05-06)

From what I understand of current models, the bulge of the galaxy formed first, and thus, would contain older population II like stars. Currently, however, the halo has a higher population of stars with lower metalicity than the bulge. Is this because the density of stars in the bulge is much higher? My thinking is that this is a densely populated region of massive hot stars that die quickly and create a newer region of next generation population I stars that are metal rich. The inverse would be true for the halo where stars are less densely packed. Is this correct?

**Tags:** star, stellar-evolution, metallicity


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## 1 answers

### Answer by username_1 on 2016-05-08. Score: 2 | Accepted answer

Your intuition is largely correct: the key is that the proto-bulge region had a deep enough potential well so that the supernovas couldn't expel the remaining gas, and so new stars could form out of the gas (enriched by the supernova ejecta) in a continuing cycle. In the low-mass, isolated protogalactic clouds which probably contributed to the halo, the initial round of supernovas ejected most of the gas (including the original gas that hadn't yet formed stars) -- thus, little opportunity to form more stars (out of higher-metallicity gas) on a continuing basis.

It's really the total mass in a given region that matters. For example, the density of stars in the central regions of a globular cluster is pretty high, but the mass of the cluster as a whole isn't enough to keep most of the gas when its massive stars go supernova.

(Side note: the traditional terms "Population I" and "Population II" aren't used all that much any more, since age and metallicity can vary continuously and aren't always strongly associated.)

> **Comments:**
> **username_0**: That makes perfect sense. Are there any articles or readings that you know of that I could read for further understanding?  

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