Celestial hemisphere:  Southern  ·  Constellation: Aquarius (Aqr)  ·  Contains:  NGC 7184
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NGC 7184, Gary Imm
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NGC 7184

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NGC 7184, Gary Imm
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NGC 7184

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Description

This object is a rarely imaged barred spiral galaxy located 100 million light-years away in the constellation of Aquarius at a declination of -21 degrees. This is a huge galaxy. The width in our apparent view is 6 arc-minutes, which corresponds to a true diameter of 175,000 light years. The bar through the core is along our line of sight, which makes it difficult to see unless you look closely.

Three aspects of this galaxy stand out to me. The first is the bright inner ring. The galaxy look symmetric to me with no gravitation distortion from other galaxies, so at first I wasn't sure what mechanism causes this unique distinct ring in this galaxy. But then I read that some scientists believe that the tiny edge-on bright galaxy just above the core is actually a dwarf satellite of NGC 7184. Its diameter of 10,000 light years is only a fraction of the main galaxy and could explain the interesting structure of NGC 7184. The redshift values of these galaxies are consistent with this logic, although I am a bit puzzled because I have never seen a dwarf satellite galaxy with such a distinct spiral shape. Visually, it looks more like a far distant larger galaxy to me.

The second aspect I like about this galaxy is the very subtle color change as you move through the galaxy out from the core (yellow), to the middle star forming HII regions (reddish) to the outer edge star clusters (bluish).

The third aspect I like about this galaxy is hard to detect because of our view perspective. It looks to me like the mid to outer region of the galaxy disk is darker on the near side and far side of the galaxy, as opposed to the right and left side of the galaxy. This corresponds to each end of the bar across the core, which perhaps is the driving mechanism. As a result, the outer disk is not an oval but is pinched across the middle, more like a figure 8.

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