Object of the Week May 8, 2022 - NGC 4725 TIE Fighter Galaxy

NGC 4725, UGC 7989, CGCG 129-027, MCG +04-30-022
Constellation: Coma Berenices
Type: Peculiar Mixed Spiral Galaxy
Classification: SAB(r)ab pec
RA: 12h 50.4m
DEC: 25° 30'
Mag: 9.4v
Size: 11.0' x 8.3’

Diary entry for May 4, 2022

• Happy Star Wars Day!
• Researching my pick for the upcoming OOTW, NGC 4501, aka Messier 88, in Coma Berenices
• Came across this one sentence mention of another galaxy on an obscure and somewhat dated astrophotography blog:
• “Another popular target…it is a strange spiral in the Coma Berenices constellation that apparently has only one spiral arm.”
• Going off track, however I feel compelled to find out more about this peculiar galaxy.
• Digging through my astro library I find is a sketch of it in the interstellarum Deep Sky Guide
• What? No way! You gotta to be joking?! This? Oh yes…this is the TIE Fighter Galaxy
• Presumably named by author and sketcher, Uwe Glahn?
• Sorry M88 you’re out for now, maybe next time
• NGC 4725 you’re in this week
• May the Fourth be with you/me/us

End of diary entry

How many of you have observed NGC 4725? Few I’m willing to bet. By the way I checked my log and I can tell you that I haven’t. This is somewhat surprising when you consider that the only galaxy in Coma Berenices brighter than it is M63. This caused Stephen James O’Meara to ponder, “How NGC 4725 escapes notice is almost beyond imagining. The fact is, the galaxy is like a leaf floating on the edge of a stream, it’s far enough away from the rushing madness that it takes an auto of serendipitous concentration to notice it - that is, or course, unless someone points it out to you.”

NGC 4725 was discovered by William Herschel in 1785 nearly two centuries before the invention of the TIE fighter. His observation of April 6, 1785 was logged as H I-84 and reads: “Considerably bright, irregularly round, small brighter middle, milky, 7’ or 8’ diameter.” The inner ring was first detected by Lord Rosse in the mid 1800s, who observed the galaxy in his 72-inch Leviathan reflector at Birr Castle in Ireland. He not only noticed that NGC 4725 had an inner ring, but he also said that it was an “incomplete” oval.

NGC 4725 is classified as a Peculiar Mixed Spiral Galaxy. O’Meara describes its morphology the best. “In photographs, NGC 4725 is a stunning example of a transition galaxy between a normal spiral and barred spiral. If you look closely at the central lens, you will see that there is no well-defined bar. There is, however, a very small, extremely bright nucleus in a faint, smooth, broad bar with dark lanes, Also centers on the bar is the galaxy’s most stunning feature - a high-surface=brightness spiral pattern that forms an almost complete ring inclined 43d from face-on; this feature is, in fact, one of the most complete near-rings of any galaxy known. The galaxy’s amorphous central region - across which slice weak ripples of dust - and breaks into multiple, tightly wound spiral arms studded with rich star-forming regions. Therefore the basic structure of NGC 4725 is closer to that of a normal spiral than that of a barred spiral. On long-exposure images, two very faint external arms (generally smooth in texture with only hints of star-forming regions) loop almost completely around the bright central ring. These external arms are not on opposite sides of the nucleus but travel together, one lapped on the inside of the other. They are also branched. The principal one is an extension of a bright western inner arm, which forms part of the nearly complete inner ring. This arm branches into two, which then gradually unwind for about 200°.”


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Images of NGC 4725 provide us with incredible views and some insight into the complex nature of this galaxy, but it also leaves us with a lot to unpack. The best way to unpack it for yourself is get out under a dark sky and observe the galaxy for yourself. The galaxy is bright enough to be detected with the smallest of apertures, starting with 7 x 50 binoculars. A telescope of 10-inches or greater will begin to yield some of the remarkable structure of this galaxy. To whet your appetite I’ll share a few observations from several well known observers.


Bertrand Laville
Deep Sky Forum member
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You'll find Bertrand's detailed notes on NGC 4725 here


Ivan Maly
Deep Sky Forum member
Attachment 4681


Christian B. Luginbuhl and Brian A. Skiff
Observing Handbook and Catalogue of Deep-Sky Objects
Visible in 6 cm, this large galaxy is elongated NE-SW, about 8'×6, and very little concentrated except for a small brightening in the center. It is about 7' × 5' in 15 cm with a small brighter core. The galaxy is quite bright in 25 cm, appearing as a 5' × 3' haze with a central stellar nucleus but no core. A mag. 12.5 star lies 2.5 N; a threshold magnitude star is on the E edge. 30 cm shows a l’ core and stellar nucleus with the faint halo extending to 4'5 × 3' in pa 45°. The star 1'5 E of center is about mag. 14.5. Broad brightenings are visible at the acute ends of the halo 2' from the nucleus, each about l' diameter. A slight brightening along the major axis connects these with the core. The halo is oval and has extremely faint extensions to about 7' length. eg 4712, q.v., lies 12' W; eg 4747, q.v., 24' NE.


George Keeple and Glen Sanner
The Night Sky Observers Guide: Volume 2 Spring & Summer
12”/14” scopes @125x: NGC 4725 is quite large and bright, appears elongated 10’ x 7’ NE-SW, and has a bright, sharp nucleus in a bright but small core. Its broad spiral arms form a ring around the interior of the galaxy, the ring brightest alongs its NE and SW arcs. A very faint central bar may be glimpsed in the core of the galaxy elongated, like the halo, NE-SW. A magnitude 12.5 star lies 2.5’ NNW, and magnitude 14.5 stars are superimposed upon the halo 1.5’ east and 2’ NE on the galaxy’s center.


Who tagged NGC 4725 with the nickname TIE Fighter Galaxy? The interstellarum Deep Sky Guide by Ronald Stoyan and Uwe Glahn has been the only catalog I’ve found that references this name. However I have not yet been able to confirm my supposition with the authors.

Why was NGC 4725 nicknamed TIE Fighter Galaxy? First look at the sketch of a TIE fighter, then look at this image of the galaxy as well as the sketches above from Bertrand and Ivan. Do you see the resemblance to the TIE fighter?

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Now it is your turn. Give it a go, let us know and may the force be with you!

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I have no idea how this object landed on my observing list, but it did, and I therefore observed it last new moon from the Bortle 2 skies of Death Valley National Park on Apr 1st 2022 (not a joke).

I wish I had noted that this was of such interesting morphology, and I may have paid attention to details like the face on part being oriented at an angle to the "bar". If you look at my sketch, I did not -- I just sketched it as a barred spiral because I perhaps let my preconceived notions of what galaxies are supposed to look like get in the way of observing.

Observing it with a 10" at 117x back in 1988 showed it to be elliptical in shape with a bright nucleus.

Hi, here's my observation from 5/5/2016: Ngc 4725 galaxy in Coma Bernices ; magnitude:9.4 ; large bright face on ; bright nucleus with broad spiral arms , that form a ring around the exterior ; some stars were observed superimposed over the galaxy. I used a 10mm Ethos at 198x with my 14.5 Starstructure f/4.3Attachment 4693

The fist time I read about this object referred to as TIE fighter was in an article by Sue French in Sky& Tel.

From the 12.5" notes:
lrg, bright, oval, sml stellar core in oval glow, diffuse edges, spiral @45 deg?, some mottling near edges, best view 228x, in field w/4712 and 4747--brightest and largest of the 3.

Two observations to contribute through my 18" in 2007 and second through Jimi's 48" on 3 May 2019 during TSP week. Also observing with us were Howard Banich and Bob Douglas and I believe a few other TSP participants, so I probably just took a brief look.

18" (5/12/07): very impressive spiral structure visible. Two arms emerge from the very bright oval core (not interpreted as a bar). One arm is attached at the NE end of the core and sweeps to the north before hooking back to the west. Three faint stars are superimposed along this arm. A second broader arm is attached at the SW end of the core. This arms heads south before hooking towards the east. Both arms have brighter patches or arcs near the ends of the major axis.

48" (5/3/19): very bright, very large, oval 3:2 SSW-NNE, strong concentration with a very bright oval core and an intense nucleus. The inner ring (interpreted as spiral arms in my 18" observation) was very obvious and highlighted by bright arcs or "handles" at the SW and NE ends. The ring dimmed on the east side but was connected between the two arcs/arms. The western side, though, had a missing gap. At least one HII knot was seen on the SW end [2.1' WSW of center], perhaps NGC 4725:[BKB2006] 11, which is in the spiral arm immediately to the west. A faint HII region was also noted on the NE end of the ring, probably NGC 4725:[BKB2006] 4. These designations are from a 2006 catalog of HII regions by Bradley et al. The outer halo had a very low surface brightness and was ill-defined.

To go along with Steve's top notch description above, here's my sketch, and much briefer notes, of the view through Jimi's 48-inch two years ago. Note that the sketch is an impression rather than a detailed representation because I sketched it from memory after climbing down the ladder from the eyepiece.

"Big but subtle, what an incredible shape! Bright core, everything else is much more subtle. 9mm Nagler, 21.82 SQM."

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I also have a few observations with my old 20-inch and 28-inch, but not surprisingly, this view through Jimi's 48-inch far surpasses them.

Quote:

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Originally Posted by Howard B

To go along with Steve's top notch description above, here's my sketch, and much briefer notes, of the view through Jimi's 48-inch two years ago. Note that the sketch is an impression rather than a detailed representation because I sketched it from memory after climbing down the ladder from the eyepiece.

"Big but subtle, what an incredible shape! Bright core, everything else is much more subtle. 9mm Nagler, 21.82 SQM."

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I also have a few observations with my old 20-inch and 28-inch, but not surprisingly, this view through Jimi's 48-inch far surpasses them.

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Looking at this sketch, I already want to be back in Fort Davis!

I don't know exactly where Ronald had the term "TIE Fighter Galaxy", but it easily could be the idea came from Sue and he collected all the known and more or less common names which he later published in the isDSG.

With the 16-inch the shape of the "TIE Fighter" was barely visible with hints of the fainter outer regions.

sketch: 16", 180x-257x, NELM 6m5+, Seeing III
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