Starship Asterisk*

Polar Ring Galaxy NGC 2685

Explanation: NGC 2685 is a confirmed polar ring galaxy - a rare type of galaxy with stars, gas and dust orbiting in rings perpendicular to the plane of a flat galactic disk. The bizarre configuration could be caused by the chance capture of material from another galaxy by a disk galaxy, with the captured debris strung out in a rotating ring. Still, observed properties of NGC 2685 suggest that the rotating ring structure is remarkably old and stable. In this sharp view of the peculiar system also known as Arp 336 or the Helix galaxy, the strange, perpendicular rings are easy to trace as they pass in front of the galactic disk, along with other disturbed outer structures. NGC 2685 is about 50,000 light-years across and 40 million light-years away in the constellation Ursa Major.

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I would think that somebody over there, has an interesting night sky....

What ANGLE would another galaxy have to come in at to produce such a thing?

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Great picture! I'm always happy to see a picture by Ken Crawford here.

It is interesting to see those thin "dust arms" silhuetted againt the main "body" of the galaxy. Many spiral arms are like that: they are mainly made up of long thin dust structures, which only occasionally form new bright stars.

Ann

Boomer12k wrote: What ANGLE would another galaxy have to come in at to produce such a thing?

Simulations show that such a structure is longer-lasting the more nearly the shredded former companion is to orbiting right over the poles of the main galaxy disk. This happens because of differential precession - just as with Earth's poles, the flattened gravitational field of the galaxy exerts a torque on the orbit of surrounding material, which depends both on the orbital radius and the angle between the orbit and plane of the galaxy disk. For polar orbits, there is no precessional effect, so the material hangs there in orbit for very long times. Non-polar disks occur, but they become smeared out into more complex warped configurations (NGC 4753 is a wild example which looks just like the simulations) and can settle faster toward the main galaxy's disk plane.

(Synchronicity - just had some examples of these warped precessing disks show up in Hubble data so it was on my mind).

Boomer12k wrote:I would think that somebody over there, has an interesting night sky...

Not so much, I think. I doubt that the perpendicular structures are even bright enough to be apparent to the naked eye, or if they are, they would be very subtle and dim compared with the Milky Way-like band created by the surviving disc of the original galaxy (itself probably spread out and unimpressive compared with the appearance of the Milky Way band in our own sky).

This is a very pecualiar Galaxy. The polar ring is
interesting. The galaxy has 50,000 light years of
diameter, but what is the diameter of the polar ring?

What an incredible picture! Anyone else think this should be called the football galaxy?

http://ned.ipac.caltech.edu/level5/Arp/ ... rp336.jpeg
I concur! This is indeed a peculiar galaxy.

http://ned.ipac.caltech.edu/help/faq3.html#3a - Never heard of "Galactic Extinction" before. Lots of papers to read. I presume galactic extinction is not at all like dinosaur species extinction.

Psnarf wrote: Never heard of "Galactic Extinction" before. Lots of papers to read. I presume galactic extinction is not at all like dinosaur species extinction.

The collision involved is much smaller in the case of the dinosaurs.

Excellent suggestion, Nathan! I note it is shaped more like a football than just having a polar ring. I wonder if a passing galaxy (or a galaxy that was destroyed while attempting to pass) was actually successively stripped of material in a sequence, producing something like the threads on a screw. But it also looks to me like it is a barred galaxy.

I think it would be really helpful to observe this galaxy over a long time, to ascertain the motions of the various parts.

You folks never cease to amaze us with wonderful images of our fascinating universe!

NGC3314 wrote:

Boomer12k wrote: What ANGLE would another galaxy have to come in at to produce such a thing?

Simulations show that such a structure is longer-lasting the more nearly the shredded former companion is to orbiting right over the poles of the main galaxy disk. This happens because of differential precession - just as with Earth's poles, the flattened gravitational field of the galaxy exerts a torque on the orbit of surrounding material, which depends both on the orbital radius and the angle between the orbit and plane of the galaxy disk. For polar orbits, there is no precessional effect, so the material hangs there in orbit for very long times. Non-polar disks occur, but they become smeared out into more complex warped configurations (NGC 4753 is a wild example which looks just like the simulations) and can settle faster toward the main galaxy's disk plane.

(Synchronicity - just had some examples of these warped precessing disks show up in Hubble data so it was on my mind).

NGC 4753 is a really weird and cool galaxy with a multitude of visual peculiarities with twisted dark lanes, outer tidal plumes and I think it has a strange Ha structure. This is a galaxy I would love to see a deep image of by Ken Crawford!!

MarkBour wrote:Excellent suggestion, Nathan! I note it is shaped more like a football than just having a polar ring.

There we go with 'That' shape, again. Round, triangle, square, oblong, circular, etc, but I don't believe 'football' is a shape. Most of planet Earth's residents think a football is shaped exactly like a soccer ball. Yes, APOD is a gift from the U. S. A. however its viewers are worldwide. I could picture interplanetary creatures shaped like Patrick Star and Squidward playing soccer but, as they lack feet I have trouble viewing them playing American style football. I don't think the game is destined to go intergalactic.

The shape discussion occurred before. I recall no resolution.

BillBixby wrote:

MarkBour wrote:Excellent suggestion, Nathan! I note it is shaped more like a football than just having a polar ring.

There we go with 'That' shape, again. Round, triangle, square, oblong, circular, etc, but I don't believe 'football' is a shape. Most of planet Earth's residents think a football is shaped exactly like a soccer ball. Yes, APOD is a gift from the U. S. A. however its viewers are worldwide. I could picture interplanetary creatures shaped like Patrick Star and Squidward playing soccer but, as they lack feet I have trouble viewing them playing American style football. I don't think the game is destined to go intergalactic.

The shape discussion occurred before. I recall no resolution.

Thanks for bringing it up again.

Personally, I prefer the shape of the Australian Rules football, aka, the "Sherrin" after its best known maker. Since Aussie Rules footy is the best form of football played on this planet, and since most people who see it for the first time think that it must have been invented by aliens, I suspect when said aliens come back we'll find that is their preferred field game, not that diving exhibition that some people call the beautiful game.

'Nuf said?

Rob

rstevenson wrote:Personally, I prefer the shape of the Australian Rules football, aka, the "Sherrin" after its best known maker. Since Aussie Rules footy is the best form of football played on this planet, and since most people who see it for the first time think that it must have been invented by aliens, I suspect when said aliens come back we'll find that is their preferred field game, not that diving exhibition that some people call the beautiful game.

'Nuf said?

Rob

The galaxy is shaped like a prolate spheroid (as is the "Sherrin").

But regarding football, I'm a Rugby fan (of both the Wallabies and the All Blacks, which might actually be illegal). Soccer (or Association Football, to give it its formal name) would be much more interesting if they got rid of the goalies or made the goals bigger -- too much passion over too few points. I'd rather watch chess than watch American Football. And Australian Football is fun to play and the balls are fun to kick, but I don't like watching it much. Australian Football does possibly have the best claim to the word "football", as a goal can only be scored coming off the foot, but there may be more kicks in the average Soccer game.

Chris Peterson wrote:

Boomer12k wrote:I would think that somebody over there, has an interesting night sky...

Not so much, I think. I doubt that the perpendicular structures are even bright enough to be apparent to the naked eye, or if they are, they would be very subtle and dim compared with the Milky Way-like band created by the surviving disc of the original galaxy (itself probably spread out and unimpressive compared with the appearance of the Milky Way band in our own sky).

Back to the galaxy (if that is possible)...

According to the version of Principal Galaxy Catalog that my software links to (and which may or may not be terribly updated), NGC 2685 is a smallish galaxy, definitely smaller than the Milky Way. It is clearly bigger than the Large Magellanic Cloud (again assuming that the information in Principal Galaxy Catalog is accurate), but clearly smaller than the Milky Way. It is about 30% as luminous as our own galaxy and therefore likely clearly smaller.

So, to return to the real question of this thread, is NGC 2684 a football? Well, to the aliens hiding themselves as galaxy clusters, NGC 2685 is probably a football of just the right size.

Face of alien masquerading as galaxies M86, M84 and NGC 4388, with bystander off to the left.

Ann

Nitpicker wrote: The galaxy is shaped like a prolate spheroid.

Or not. It shows a significant velocity gradient end-to-end, just like an S0 lenticular galaxy of that luminosity seen edge-on. If it's prolate, the shape has to be tumbling at this rate.

NGC3314 wrote:

Nitpicker wrote: The galaxy is shaped like a prolate spheroid.

Or not. It shows a significant velocity gradient end-to-end, just like an S0 lenticular galaxy of that luminosity seen edge-on. If it's prolate, the shape has to be tumbling at this rate.

I'm certainly not going to argue with that, as I know four fifths of nothing about galaxies. I was mainly just trying to provide a better name for the shape of a football, and I think "prolate spheroid" is it. However, if the galaxy is not like a volume of revolution, then it would probably be more like a mere ellipse, which is a problem, as that name is already in use to classify galaxies. I think I'm spent.

The only thing clear to me is that some people are upset that Americans have their own version of a football which is long and has slightly pointed ends and happens to be a familiar shape which can be used as an adjective and the rest of the world wants to tell us we are wrong because their footballs are perfect spheres. You have to get very verbose to describe the actual shape of a football, which is a prolate spheroid with some pinched ends. Gosh, I have been through this before. It makes me angry.

I can't speak for everybody, but I'm not upset or angered by the American football (they are fun to throw). I thought the issue was just that the term "football" is vague and localised, so the geometry of a "football" is not well defined, and should therefore be avoided as a descriptor. Similarly, I have been confused by Australian football nuts who describe shapes to me as "like a footy field". They are really trying to say "ellipse", but as a Rugby fan, I naturally think "rectangle".

I think an American football is closer to a sinusoidal or parabolic volume of revolution. But Rugby and Australian footballs are closer to prolate spheroids. No big deal.

One could interpret the galaxy with pointy or rounded ends, I think.

Plenty of things are localized (otherwise known as culture) but when the football thing comes up, suddenly it is a Big Deal and an argument must be had because this sport or that sport is The Sport. The Toby Jug nebula never had any issues. What the hell is a Toby Jug? I can't see a Toby Jug in the Toby Jug nebula no matter how hard I look. They should have named that the Two Tangential Arcs Nebula so I would have never had to suffer such mental anguish over the name. Bah, if Nathan or anyone wants to call this the (American) Football Galaxy because that's what it looks like, go for it, I say.

geckzilla wrote:Plenty of things are localized (otherwise known as culture) but when the football thing comes up, suddenly it is a Big Deal and an argument must be had because this sport or that sport is The Sport.

I suggest ending the debate and agreeing it doesn't look that much like any sort of football, unless some version is played with a transparent one. Clearly, this should be called the Ctenophora Galaxy.

Call the galaxy by whatever name you like. The Football Galaxy is as good a name as any other.

There has obviously been a misunderstanding. My point was only that the word "football" is a poor word to describe a shape, not just because of cultural variations, but because it is not sophisticated enough for my high-brow sensibilities. Naming a galaxy is fundamentally different: whatever sticks, wins.

I'm sorry we angered you with our low-brow, pseudo-tribal, cultural discussion on the various codes of football. We're a flawed species, remember?

I was actually annoyed by BillBixby's post. This happened multiple times before at Asterisk prior to your arrival, Nit. I will be sure to reference Ctenophora next time it happens.