APOD: UGC 1810: Wildly Interacting Galaxy... (2020 Oct 18)

[APOD Robot]

UGC 1810: Wildly Interacting Galaxy from Hubble

Explanation: What's happening to this spiral galaxy? Although details remain uncertain, it surely has to do with an ongoing battle with its smaller galactic neighbor. The featured galaxy is labelled UGC 1810 by itself, but together with its collisional partner is known as Arp 273. The overall shape of UGC 1810 -- in particular its blue outer ring -- is likely a result of wild and violent gravitational interactions. This ring's blue color is caused by massive stars that are blue hot and have formed only in the past few million years. The inner galaxy appears older, redder, and threaded with cool filamentary dust. A few bright stars appear well in the foreground, unrelated to UGC 1810, while several galaxies are visible well in the background. Arp 273 lies about 300 million light years away toward the constellation of Andromeda. Quite likely, UGC 1810 will devour its galactic sidekick over the next billion years and settle into a classic spiral form.

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[heehaw]

Now THAT'S what I call a GALAXY!

[JohnD]

The usual future for colliding galaxies is said to be as a globular cluster. This seems so strongly spiral, that seems unlikley, so what's the difference?

[sillyworm 2]

Is the smaller galaxy in the arm also part of this merge? The main 2nd merging galaxy is not shown in this apod?

[Chris Peterson]

The usual future for colliding galaxies is said to be as a globular cluster. This seems so strongly spiral, that seems unlikley, so what's the difference?

Large galaxy mergers usually produce elliptical or irregular galaxies, losing the spiral structures of the progenitors (probably forever). But when a large spiral is disrupted by a small galaxy, the latter may be incorporated and the large one may settle back into a stable spiral again.

(Globular clusters are not the product of colliding galaxies.)

[Snarf]

I only see one (1) galaxy. I wish you people would annotate this stuff!

[johnnydeep]

UGC 1810: Wildly Interacting Galaxy from Hubble

Explanation: What's happening to this spiral galaxy? Although details remain uncertain, it surely has to do with an ongoing battle with its smaller galactic neighbor. The featured galaxy is labelled UGC 1810 by itself, but together with its collisional partner is known as Arp 273. The overall shape of UGC 1810 -- in particular its blue outer ring -- is likely a result of wild and violent gravitational interactions. This ring's blue color is caused by massive stars that are blue hot and have formed only in the past few million years. The inner galaxy appears older, redder, and threaded with cool filamentary dust. A few bright stars appear well in the foreground, unrelated to UGC 1810, while several galaxies are visible well in the background. Arp 273 lies about 300 million light years away toward the constellation of Andromeda. Quite likely, UGC 1810 will devour its galactic sidekick over the next billion years and settle into a classic spiral form.

Uh, where's the "galactic sidekick"? Oh, there it is in the pic from the wikipedia link for Arp 273 (and also in the other APOD link):



Which makes it well out of the top of the frame of this APOD pic.

[johnnydeep]

I only see one (1) galaxy. I wish you people would annotate this stuff!

Indeed. The companion galaxy is not even in the picture! See my prior post.

[Eclectic Man]

If there have been "wild and violent" gravitational interactions distorting the orbits of the stars, does that mean that each star's equivalent of an Oort Cloud and Kuiper belt have been perterbed and any planetary bodies are (were) being pummelled by millions of rocks and comets? If so it would mean any planetary life in these systems was being severely damaged.

[Chris Peterson]

If there have been "wild and violent" gravitational interactions distorting the orbits of the stars, does that mean that each star's equivalent of an Oort Cloud and Kuiper belt have been perterbed and any planetary bodies are (were) being pummelled by millions of rocks and comets? If so it would mean any planetary life in these systems was being severely damaged.

Large sections of these galaxies experience only very tiny tidal forces across the scale of a solar system (< 1 ly). The distortions we see are on the scale of thousands of light years. But certainly, during an actual collision, there will be regions where stars pass close to one another, disrupting all of the orbiting bodies around those stars, not just the most distant ones. Not good for any life on them, especially not complex life.

[Psnarf]

The hot blue stars "have formed only in the past few million years" yet the galaxy is "300 million light years away." Sew! the hot blue stars formed in the galaxy's time frame a couple of million years ago, which we observe 300 million years later, a couple of million years plus 300 million years ago? Just trying to clarify what the author meant.

[Chris Peterson]

The hot blue stars "have formed only in the past few million years" yet the galaxy is "300 million light years away." Sew! the hot blue stars formed in the galaxy's time frame a couple of million years ago, which we observe 300 million years later, a couple of million years plus 300 million years ago? Just trying to clarify what the author meant.

The distance of an object is generally not relevant to discussions of time, because we almost always consider events in the time frame of the observer. It doesn't matter how long it took the light to get here. If we went back in tome a few million years, we'd see those same stars forming.

[sillyworm 2]

Again..is the smaller galaxy in the arm of the larger galaxy mergings as well or is it behind the galaxy?

[johnnydeep]

Again..is the smaller galaxy in the arm of the larger galaxy mergings as well or is it behind the galaxy?

Sorry, sillyworm 2, I was hoping someone else might provide a better answer than I can. Googling hasn’t turned up much, but this pic from https://hubblesite.org/contents/media/i ... ?news=true seems to more clearly show something interacting with the blue ring of UGC 1810 - perhaps it is a satellite dwarf galaxy:

Click to view full size image

EDIT: I did find this from http://www.astrophotolab.com/pr/g1111.htm, that at least mentions the “knot” in the spiral arm as possibly caused by a “mini spiral”:

A possible mini-spiral may be visible in the spiral arms of UGC 1810 to the upper right. It is noticeable how the outermost spiral arm changes character as it passes this third galaxy, from smooth with lots of old stars (reddish in color) on one side to clumpy and extremely blue on the other. The fairly regular spacing of the blue star-forming knots fits with what is seen in the spiral arms of other galaxies and is predictable based on instabilities in the gas contained within the arm.

[JohnD]

The usual future for colliding galaxies is said to be as a globular cluster. This seems so strongly spiral, that seems unlikley, so what's the difference?

Large galaxy mergers usually produce elliptical or irregular galaxies, losing the spiral structures of the progenitors (probably forever). But when a large spiral is disrupted by a small galaxy, the latter may be incorporated and the large one may settle back into a stable spiral again.

(Globular clusters are not the product of colliding galaxies.)

Thnak you, Chris!

[Ann]

Again..is the smaller galaxy in the arm of the larger galaxy mergings as well or is it behind the galaxy?

UGC 1810, the APOD of October 18, 2020.

Arp 273. NASA, ESA and Z. Levay

Sorry, I've been remiss. I should have said something about what is now yesterday's APOD, but I'm sorry to say I lost interest in it when I saw that it seemed to be a two-filter image. Also I knew that there is a relatively large galaxy interacting with UGC 1810 that was not visible in the APOD, and I just didn't feel like commenting.

But you are so right about the mini spiral in one of the arms of UGC 1810. It does look as if it is located squarely in one of the spiral arms of UGC 1810, and it does indeed look as if it is "interfering" with the star formation in this arm. Note how there are bright regions of star formation in the spiral arm "above" and "below" this mini spiral. Based on its appearance alone, I'd say that the mini spiral is indeed located in that arm of UGC 1810.

Also note the small quite red even tinier spiral(?) which seems to be plowing right through an arm of UGC 1810, leaving a wake behind it. But this tiny spiral is very red, casting doubt on its nature as a feature physically related to UGC 1810. It looks more like a redshift-reddened background object. The other "mini spiral" is the right color to be at the same distance from us as UGC 1810.

NGC 6050. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and K. Noll (STScI).

---

UGC 1810 is not the only spiral galaxy to contain a mini spiral galaxy located in one of its arms. The prime example of this feature is NGC 6050. NGC 6050 is actually a triple galaxy: There is one galaxy with extensive spiral arms and a large yellow bulge and center, one galaxy with extensive and very blue star forming spiral arms and a very faint bulge cut in half by a thin yellowish bar, and one much smaller barred spiral galaxy nested inside one large arm that seems to connect the two other galaxies.

The little galaxy nested inside the arm connecting the two other galaxies has a central bar that is just as bright as the thin bar of the larger galaxy that is all spiral fluff and little central substance.

So yes, I'd say that it is indeed possible for little spirals to be located inside arms of much larger spirals.

Ann

[sillyworm 2]

Thanks everyone....just thought it odd that there is no mention of it in a description or the apod.