Galactic onion

The glowing object in this image is an elliptical galaxy called NGC 3923. It is located over 90 million light-years away in the constellation of Hydra.

NGC 3923 is an example of a shell galaxy where the stars in its halo are arranged in layers.

Finding concentric shells of stars enclosing a galaxy is quite common and is observed in many elliptical galaxies. In fact, every tenth elliptical galaxy exhibits this onion-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop as a consequence of galactic cannibalism, when a larger galaxy ingests a smaller companion. As the two centres approach, they initially oscillate about a common centre, and this oscillation ripples outwards forming the shells of stars just as ripples on a pond spread when the surface is disturbed.

NGC 3923 has over twenty shells, with only a few of the outer ones visible in this image and its shells are much more subtle than those of other shell galaxies. The shells of this galaxy are also interestingly symmetrical, while other shell galaxies are more skewed.

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.

Credit:

ESA/Hubble & NASA
Acknowledgement: Judy Schmidt

About the Image

Id:potw1519a
Type:Observation
Release date:11 May 2015, 10:00
Size:4010 x 4040 px

About the Object

Name:NGC 3923
Type:Local Universe : Galaxy : Type : Elliptical
Distance:90 million light years
Constellation:Hydra
Category:Galaxies

Image Formats

Large JPEG
3.7 MB
Screensize JPEG
149.4 KB

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Coordinates

Position (RA):11 51 2.77
Position (Dec):-28° 48' 26.84"
Field of view:3.35 x 3.37 arcminutes
Orientation:North is 14.6° right of vertical

Colours & filters

BandWavelengthTelescope
Optical
V
606 nm Hubble Space Telescope
ACS
Infrared
I
814 nm Hubble Space Telescope
ACS

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