Celestial hemisphere:  Northern  ·  Constellation: Pisces (Psc)  ·  Contains:  NGC 125  ·  NGC 126  ·  NGC 127  ·  NGC 128  ·  NGC 130
Getting plate-solving status, please wait...
NGC 128 Galaxy Group, Gary Imm
Powered byPixInsight

NGC 128 Galaxy Group

Getting plate-solving status, please wait...
NGC 128 Galaxy Group, Gary Imm
Powered byPixInsight

NGC 128 Galaxy Group

Equipment

Loading...

Acquisition details

Loading...

Description

This object is a rarely imaged galaxy cluster located 190 million light years away in the constellation of Pisces at a declination of +3 degrees.

The cluster is anchored by NGC 128, a lenticular galaxy with a width of 3 arc-minutes in our apparent view, which corresponds to a large diameter of 160,000 light years. This galaxy is certainly one of the most fascinating I have ever seen. It has a strong visible tidal bridge with NGC 127. Even more interesting, though, is the "X" shape across the core of the galaxy. This is really puzzling to me. There is some conjecture that this unique shape is caused by the gravitational effects of the two nearby galaxies (NGC 127 and NGC 130), but the shape seems too "clean", with no extended star streams beyond the "X", and NGC 130 not distorted at all.

Upon further investigation, I came across a fascinating 1987 paper, "IC 4767 (The X Galaxy): The Missing Link for Understanding Galaxies with Peanut-Shaped Bulges?", by Whitmore and Bell. Here is a key quote - "The peculiarities in both cases have the same origin: the accretion of material from a companion galaxy during a merger or tidal encounter. If the accreted material impacts the central galaxy at nearly a right angle to the disk, a polar-ring galaxy is produced. If the accreted material impacts the central galaxy at an oblique angle, a galaxy with a box-shaped or peanut-shaped bulge may be produced."

And sometimes, for the later case, the bulge actually resembles an "X" for a specific angle of projection - "The oblique disk spreads out into a precession cone. This cone-like structure will appear to form an X-shape when seen in projection. A simple way to convince yourself of this is to spin a coin on a table (a penny works best because it is darker). Just before it settles to the table, the coin will show a distinct X shape when viewed from the side." I tried it, and now I am convinced!

So, it seems that this unique X-shape is not entirely unique, and is due to the specific orientation of interaction (and our projected view of it) between NGC 128 and the companion NGC 127 to the right.

To the lower right, two more galaxies also have very interesting star streams - NGC 126, and NGC 125 (furthest right). Several other smaller galaxies are also visible in the background.

Comments