A Hubble closeup of the central region of any galaxy is always very valuable. I'm always very grateful for every galaxy portrait made by Hubble.
If there is a future core-collapse supernova in the central parts of NGC 3521, this Hubble picture may show the progenitor of that supernova.
Today's APOD shows the chaotic distribution of dust in the inner regions of NGC 3521. This makes NGC 3521 a so-called flocculent galaxy
. The closeup of this chaotic dust is also valuable.
NGC 3521. Photo: R Jay GaBany, David Martinez-Delgado et al.
In the case of NGC 3521, the outer regions of it, which can't be seen in the Hubble image, are very interesting. In the picture by R Jay GaBany at left, note the billowing yellow halo "above and below" the bulge of NGC 3521. This yellow halo is made up of possibly billions of mostly small red dwarf stars. Extremely few spiral galaxies have this sort of bright and chaotic yellow halo. Note at the edge of the disk at right the billowing clouds of old to intermediate stars, which are less yellow in color. There is also a corresponding "smoke ring" of stars at the left edge of the disk. Also there are several large shells surrounding NGC 3521. This galaxy has undergone a major event of disturbance.
NGC 4414. Photo: Adam Block.
Fascinatingly, another well-known flocculent galaxy (and another Hubble poster child
), NGC 4414, turns out to sit in the middle of several huge shells.
Personally I have to wonder if the flocculent inner structure has anything to do with the large outer shells. Another flocculent galaxy with the same kind of large outer shell is NGC 2775. Check out this page
by Adam Block to see it.