Focus On NGC 6240

The Rumpled Starfish Galaxy

For telescopes 10-inches or larger

I came across this faint, obscure galaxy quite by accident. In May 2000 I received IAUC 7428, which announced the possible discovery of a radio supernova in NGC 6240. It mentioned a position relative to the "southern nucleus" which piqued my interest. Galaxies don't typically have more than one nucleus...

I had other things to do that afternoon so I almost didn't follow up. But my curiosity got the better of me so I brought up an image of NGC 6240 using SkyView. I was immediately impressed with what I saw -- a twisted, distorted galaxy with multiple looping arcs. It immediately appeared to me like a starfish -- the rumpled ones you might find on the beach. From then on I have thought of NGC 6240 as the Rumpled Starfish Galaxy.

My mind raced. But what did it look like in the eyepiece? Were the arcs, the limbs of the starfish, visible? And what of that double nucleus?

I spent much of the rest of the afternoon researching my Starfish galaxy on the web. Among other things I discovered an image obtained with the ESO/MPI 2.2m telescope at La Silla, Chile (right). This image showed the chaotic blob that is apparently two galaxies in the process of merging. Two distinct nuclei are visible.

NGC 6240 caused quite a stir among professional astronomers when it was observed by the IRAS satellite to be extremely luminous in the far infrared. The NED database lists over 300 professional references to this merging pair of galaxies.

Yet I found only one visual observation of NGC 6240. It was by an experienced observer (Steve Coe) with a 13" f/5.6 telescope. He noted nothing our of the ordinary.

It just happened that I would have an excellent opportunity to observe my starfish galaxy that very evening with my 18-inch f/4.5 Dob. Would I be I wasting my time or had I stumbled onto a new and interesting object to observe visually?

NGC 6240

Right Ascension Declination Magnitude Con

Here are my first impressions of the Starfish galaxy on the night of May 24/25 under relatively transparent skies with fair to poor seeing:

At 85x the galaxy appeared as a very small faint diffuse and quite indistinct hazy spot near a 13th magnitude star. At 165x it appeared oval in shape but still very indistinct. The view in my 4.8mm Nagler (425x) was a bit disappointing. Much of the larger oval had become invisible. Instead I saw a faint round spot near the galaxy's center.

I switched to a Plossl and 2X barlow (330x), which increased the contrast somewhat. I spent a considerable amount of time looking with this combination. Eventually I began to be aware that the faint round area had two, perhaps three, stubby appendages. In particular there seemed to be something elongated in the NNE direction. I also saw something to the SE and had the consistent impression of an elongation toward the nearby 13th magnitude star.  My drawing matched the appearance of the DSS image fairly well.

The nucleus of this galaxy was very illusive. At times it made the remarkable impression of a smattering of faint stars embedded in the brighter central area--three, perhaps 4 stars that were hovering right at my ability to detect them. I'm not at all certain how to interpret these brief impressions.

The next night the seeing was somewhat better:
This difficult and interesting galaxy appeared quite different than on the previous night. It appeared larger in the 12.4mm Plossl (165x), which also revealed some of its "tentacles" (particularly the one to the north).

In contrast to my first observation my best views came in the 4.8mm Nagler (425x). The central nuclear region of the galaxy was clearly visible this time, appearing as a brighter spot, elongated roughly in the NS direction. I failed to discern the twin nuclei within it. The "tentacle" to the south was quite illusive even though it shows up well in images.

The tentative limb stretching toward the nearby star was not readily visible although at times I suspected something here. The images do show a small limb in this direction. Considering how differently some of the other limbs appear to my eye than in images it is possible that this limb is relatively more apparent visually.


NGC 6240 apparently represents a new,  interesting and challenging object to observe visually, particularly in larger telescopes. This galaxy can be difficult to spot at all in a 10-inch scope, which is a challenge in itself. Users of 16-inch and larger scopes should look for the arms of the starfish. How many can you count? I'm sure that others may be able to see more than I have so far.

Users of 20-inch or larger telescopes can try to be among the first to see the double nucleus. The magnitudes of these starlike objects are uncertain. I estimate something in the neighborhood of 17th magnitude. Separated by 1.6" they pose an extraordinary challenge.

Finder Charts for NGC 6240.

Millennium Star Atlas Vol III Chart 1300
Sky Atlas 2000 Chart 15
Uranometria 2000 Vol I&II Chart 247
Uranometria 2nd Ed. Chart 107
Herald-Bobroff Astroatlas B-07 C-44

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