<p>Yes, they do.</p>
<p>Bars in massive galaxies undergo a vertical &quot;buckling&quot; phase about one or two billion years after they form; when this settles down (after about a billion years), the result is that the inner 1/3-2/3 of the bar is vertically thick, with the outer part of the bar still as flat as the rest of the galaxy disk.</p>
<p>When seen side-on, the thick part of the bar looks like a peanut (double-lobed), often with a hint of an X-shape; when seen at an intermediate angle, it looks more rectangular and &quot;boxy&quot;. This is the situation <a href="http://aasnova.org/2016/08/29/featured-image-the-milky-ways-x/" rel="nofollow noreferrer">for the Milky Way</a>, in fact. (When seen with the bar end-on, the result looks very round, like a stereotypical spherical bulge.)</p>
<p>You can also see this when the galaxy <em>isn't</em> perfectly edge-on: some bars in galaxies inclined at 45 or 60 degrees (where 90 degrees = edge-on) have rectangular interiors with thinner, offset outer regions; this corresponds to the vertically thick/peanut-shaped inner part of the bar and the vertically thin outer part.</p>
<p>We've even seen the signature in a couple of galaxies of a bar in the middle of forming the peanut-shaped bulge (the <a href="http://aasnova.org/2016/07/20/do-galactic-bars-buckle-to-form-bulges/" rel="nofollow noreferrer">&quot;buckling phase&quot;</a>).</p>
<p>(In principle, you could get a boxy bulge from some kinds of minor mergers, where a small galaxy has merged with a larger galaxy. But if these exist in real galaxies, they're much rarer than the boxy bulges that are part of bars.)</p>

CC BY-SA 3.0
2017-11-12T07:57:35.133Z
Peter, you've just provided me with a couple of excellent links for my oral examination next week -- my research for my MSc in Astronomy is on the MW's X-shape!
Jim421616
CC BY-SA 3.0
2017-10-16T14:39:28.413Z
2017-10-16T14:39:28.413Z
2020-06-17T09:47:40.653Z
Peter Erwin
<p>Some face-on spiral galaxies show barred structure in their central bulges, whereas some edge-on spiral galaxies have boxy bulges. I wonder if there is any relation between these two. In particular, do boxy bulges indicate barred spirals?</p>

CC BY-SA 3.0
2017-10-16T13:28:05.747Z
Do you have an example image of what you mean by "boxy bulges"?
zephyr
<galaxy>
Do boxy bulges indicate barred spirals?
user23823
# Do boxy bulges indicate barred spirals?

(Asked by: username_0 on 2017-10-16)

Some face-on spiral galaxies show barred structure in their central bulges, whereas some edge-on spiral galaxies have boxy bulges. I wonder if there is any relation between these two. In particular, do boxy bulges indicate barred spirals?

**Tags:** galaxy

> **Comments:**
> **username_1**: Do you have an example image of what you mean by "boxy bulges"?  

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## 1 answers

### Answer by username_2 on 2017-10-16. Score: 3

Yes, they do.

Bars in massive galaxies undergo a vertical "buckling" phase about one or two billion years after they form; when this settles down (after about a billion years), the result is that the inner 1/3-2/3 of the bar is vertically thick, with the outer part of the bar still as flat as the rest of the galaxy disk.

When seen side-on, the thick part of the bar looks like a peanut (double-lobed), often with a hint of an X-shape; when seen at an intermediate angle, it looks more rectangular and "boxy". This is the situation [for the Milky Way](http://aasnova.org/2016/08/29/featured-image-the-milky-ways-x/), in fact. (When seen with the bar end-on, the result looks very round, like a stereotypical spherical bulge.)

You can also see this when the galaxy *isn't* perfectly edge-on: some bars in galaxies inclined at 45 or 60 degrees (where 90 degrees = edge-on) have rectangular interiors with thinner, offset outer regions; this corresponds to the vertically thick/peanut-shaped inner part of the bar and the vertically thin outer part.

We've even seen the signature in a couple of galaxies of a bar in the middle of forming the peanut-shaped bulge (the ["buckling phase"](http://aasnova.org/2016/07/20/do-galactic-bars-buckle-to-form-bulges/)).

(In principle, you could get a boxy bulge from some kinds of minor mergers, where a small galaxy has merged with a larger galaxy. But if these exist in real galaxies, they're much rarer than the boxy bulges that are part of bars.)

> **Comments:**
> **username_3**: Peter, you've just provided me with a couple of excellent links for my oral examination next week -- my research for my MSc in Astronomy is on the MW's X-shape!  

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