<p>The Milky Way's outer halo has many globular clusters with a retrograde orbit (about 40% of all clusters in Milky Way). One of the more prominent example include <a href="https://en.wikipedia.org/wiki/Kapteyn%27s_Star" rel="nofollow noreferrer">Kapteyn's star</a> which is highly retrograde due to it being ripped from a dwarf galaxy and merging with the Milky Way.</p>
<p>However, the structure of the halo is a topic of an ongoing debate. Several studies have claimed that the halo consists of two distinct components. The &quot;inner&quot; halo consists of more metal-rich, prograde stars and &quot;outer&quot; halo consisting of metal-poor, retrograde stars. These findings have been challenged many times due to the argument on the topic of &quot;duality of motion&quot;.</p>
<p>More readings here:</p>
<ol>
<li><a href="https://ui.adsabs.harvard.edu/abs/2007Natur.450.1020C/abstract" rel="nofollow noreferrer">Carollo et al. 2007</a></li>
<li><a href="https://ui.adsabs.harvard.edu/abs/2001A%26AT...20.1066K/abstract" rel="nofollow noreferrer">Kravtsov 2001</a></li>
<li><a href="https://ui.adsabs.harvard.edu/abs/2020A%26A...643A..69K/abstract" rel="nofollow noreferrer">Kordopatis et al. 2020</a></li>
</ol>

CC BY-SA 4.0
2021-04-18T08:31:59.330Z
very interesting thanks. Can I ask what you mean with duality of motion?
magnolia1
CC BY-SA 4.0
2021-04-18T08:40:24.373Z
also, is it at least true that the inner part contains prograde objects and the outer part retrograde? Or are they mixed? many thanks
magnolia1
CC BY-SA 4.0
2021-04-18T08:59:28.833Z
@magnolia1 duality of motion means some object moving/rotation in one direction and others in opposite directions simultaneously within a same reference frame. Some studies have noted the separation of halo into two _distinct_ components where the clusters show contrasting behaviour but it hasn't been proved yet. So, it is a subject of ongoing debate.
Nilay Ghosh
CC BY-SA 4.0
2021-04-17T10:49:32.723Z
2021-04-17T23:53:47.590Z
2021-04-17T23:53:47.590Z
Nilay Ghosh
<p>I read in papers that the Milky Way contains some retrograde stars (retrograde to the Milky Way rotation). Does anybody know where I can find a list of them, possibly including data on their distance from the Milky way center?
many thanks</p>

<orbit><orbital-mechanics><milky-way><retrograde-orbit>
Where can I find a list of retrograde Milky Way stars?
magnolia1
# Where can I find a list of retrograde Milky Way stars?

(Asked by: username_0 on 2021-04-16)

I read in papers that the Milky Way contains some retrograde stars (retrograde to the Milky Way rotation). Does anybody know where I can find a list of them, possibly including data on their distance from the Milky way center?
many thanks

**Tags:** orbit, orbital-mechanics, milky-way, retrograde-orbit


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## 1 answers

### Answer by username_1 on 2021-04-17. Score: 3 | Accepted answer

The Milky Way's outer halo has many globular clusters with a retrograde orbit (about 40% of all clusters in Milky Way). One of the more prominent example include [Kapteyn's star](https://en.wikipedia.org/wiki/Kapteyn%27s_Star) which is highly retrograde due to it being ripped from a dwarf galaxy and merging with the Milky Way.

However, the structure of the halo is a topic of an ongoing debate. Several studies have claimed that the halo consists of two distinct components. The "inner" halo consists of more metal-rich, prograde stars and "outer" halo consisting of metal-poor, retrograde stars. These findings have been challenged many times due to the argument on the topic of "duality of motion".

More readings here:

1. [Carollo et al. 2007](https://ui.adsabs.harvard.edu/abs/2007Natur.450.1020C/abstract)
2. [Kravtsov 2001](https://ui.adsabs.harvard.edu/abs/2001A%26AT...20.1066K/abstract)
3. [Kordopatis et al. 2020](https://ui.adsabs.harvard.edu/abs/2020A%26A...643A..69K/abstract)

> **Comments:**
> **username_0**: very interesting thanks. Can I ask what you mean with duality of motion?  
> **username_0**: also, is it at least true that the inner part contains prograde objects and the outer part retrograde? Or are they mixed? many thanks  
> **username_1**: @username_0 duality of motion means some object moving/rotation in one direction and others in opposite directions simultaneously within a same reference frame. Some studies have noted the separation of halo into two _distinct_ components where the clusters show contrasting behaviour but it hasn't been proved yet. So, it is a subject of ongoing debate.  

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