This
Astrobin Debut Object is a galaxy group of 4 galaxies, called Hickson 8, located 0.75 billion light years away in the constellation of Andromeda at a declination of +24 degrees.
This is a true cluster - the 4 galaxies are all at approximately the same distance. I don’t see much disturbance, so they are probably not quite close enough to each other (say, within 1 million ly) to be interacting.
Out of the 100 Hickson groups, Hickson 8 is the 14th smallest in terms of the overall spread (1.2 arc-minutes) and is the 10th furthest away.
Those of you with sharp eyes may notice that there are 7 galaxies here, not 4. The 2 galaxies at the left (edge-on spiral) and right (barred grand design spiral) sides of the image are too far away from the rest of the galaxies to be officially counted as part of the cluster, even though they are at the same distance away. Similarly, the warped edge-on galaxy near the center is not quite bright enough in magnitude to be counted. Dr. Hickson set fairly stringent criteria for galaxies to be officially counted in his clusters.
The largest and brightest galaxy of the group, Hickson 8a, is a magnitude 14 elliptical. It spans 1 arc-minute, which corresponds to a large diameter of 200,000 light years. Looking closely, you will see that this galaxy either has 2 cores or is in line with a star. It looks like a core to me and not just a superimposed star, although if this is a galaxy merger, one would expect to see more disturbance.
The Hickson catalog is a collection of 100 galaxy groups, established by Paul Hickson in 1982. Hickson compact galaxy groups are strictly defined by 3 criteria: number of galaxies, total magnitude, and isolation from other galaxies. A typical Hickson group has 4 galaxies, but some have up to 8. You can see more Hickson galaxy groups in my
Astrobin Hickson Collection.
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