<p>Globular clusters <em>formed</em> whilst the gas of the proto Milky Way was still approximately spherically distributed.</p>

<p>The gas forms a dissipative system that loses energy and collapses (within the first billion years) to a disk whilst conserving angular momentum.</p>

<p>Formed stars and clusters are essentially collisionless so the halo stars continue to have a spherical distribution, whilst more recently formed stars formed from gas already in a disk and so continue to be in a disk.</p>

CC BY-SA 3.0
2016-06-26T21:30:52.730Z
2016-06-26T21:30:52.730Z
ProfRob
<p>Globular clusters lie in the galactic halo, outside of the disc. However, galaxies are more or less a collection of material and objects — why is it, then, that most stars form a plane due to the angular momentum, but some patches of stars do not?</p>

<p>In fact, globular clusters often contain some of the earliest stars formed in a galaxy, right? How come they do not flatten, yet a lot of the older stars do?</p>

CC BY-SA 3.0
2016-06-26T17:16:49.573Z
Here's a speculation that other are free to run with if it leads anywhere. Flattening of a gravitational bound system like that requires lots of inelastic interaction between mass elements. That happens faster in a cloud of gas and dust than in a system of discrete and compact objects like stars and planets. Maybe the early formation of starts in those entities simply put them on a longer scale for thermalization of velocities.
dmckee --- ex-moderator kitten
<star><gravity><galaxy><galactic-dynamics><globular-clusters>
Why don't globular clusters flatten with a galactic disc?
Sir Cumference
# Why don't globular clusters flatten with a galactic disc?

(Asked by: username_0 on 2016-06-26)

Globular clusters lie in the galactic halo, outside of the disc. However, galaxies are more or less a collection of material and objects — why is it, then, that most stars form a plane due to the angular momentum, but some patches of stars do not?

In fact, globular clusters often contain some of the earliest stars formed in a galaxy, right? How come they do not flatten, yet a lot of the older stars do?

**Tags:** star, gravity, galaxy, galactic-dynamics, globular-clusters

> **Comments:**
> **username_1**: Here's a speculation that other are free to run with if it leads anywhere. Flattening of a gravitational bound system like that requires lots of inelastic interaction between mass elements. That happens faster in a cloud of gas and dust than in a system of discrete and compact objects like stars and planets. Maybe the early formation of starts in those entities simply put them on a longer scale for thermalization of velocities.  

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## 1 answers

### Answer by username_2 on 2016-06-26. Score: 6 | Accepted answer

Globular clusters *formed* whilst the gas of the proto Milky Way was still approximately spherically distributed.

The gas forms a dissipative system that loses energy and collapses (within the first billion years) to a disk whilst conserving angular momentum.

Formed stars and clusters are essentially collisionless so the halo stars continue to have a spherical distribution, whilst more recently formed stars formed from gas already in a disk and so continue to be in a disk.


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