APOD: Arp 188 and the Tadpole's Tail (2018 Dec 11)

APOD Robot · Post by **APOD Robot** » Tue Dec 11, 2018 5:15 am

Arp 188 and the Tadpole's Tail

Explanation: Why does this galaxy have such a long tail? In this stunning vista, based on image data from the Hubble Legacy Archive, distant galaxies form a dramatic backdrop for disrupted spiral galaxy Arp 188, the Tadpole Galaxy. The cosmic tadpole is a mere 420 million light-years distant toward the northern constellation of the Dragon (Draco). Its eye-catching tail is about 280 thousand light-years long and features massive, bright blue star clusters. One story goes that a more compact intruder galaxy crossed in front of Arp 188 - from right to left in this view - and was slung around behind the Tadpole by their gravitational attraction. During the close encounter, tidal forces drew out the spiral galaxy's stars, gas, and dust forming the spectacular tail. The intruder galaxy itself, estimated to lie about 300 thousand light-years behind the, can be seen through foreground spiral arms at the upper right. Following its terrestrial namesake, the Tadpole Galaxy will likely lose its tail as it grows older, the tail's star clusters forming smaller satellites of the large spiral galaxy.

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Karthik · Post by **Karthik** » Tue Dec 11, 2018 5:23 am

This one is bluer than previous images from the same source (Hubble Legacy Archive)

https://apod.nasa.gov/apod/ap121108.html
https://apod.nasa.gov/apod/ap140825.html

Wonder why that is and which of these depict the true colour(s) of the Tadpole.

Thanks

Ann · Post by **Ann** » Tue Dec 11, 2018 6:06 am

Karthik wrote: ↑Tue Dec 11, 2018 5:23 am This one is bluer than previous images from the same source (Hubble Legacy Archive)

https://apod.nasa.gov/apod/ap121108.html
https://apod.nasa.gov/apod/ap140825.html

Wonder why that is and which of these depict the true colour(s) of the Tadpole.

Thanks

I agree with you that the blue channel is saturated in this image.

I'd say that much of the Tadpole Galaxy isn't as dominated by young blue stars as the APOD suggests.

Normally, when you see a well-resolved image of a galaxy, you'd expect the bluest parts of it to be "prickly with stars like a hedgehog". That is because the bluest color will come from individual hot stars of extreme brightness. In a good picture, we can see these stars as individuals.

Less blue and completely non-blue parts of a galaxy will look smooth. That is because the light from these parts comes from huge numbers of relatively faint stars, which don't stand out individually.

If you take a look at the Tadpole Galaxy, you can see that there are bright individual stars in the long tail. These parts are undoubtedly blue. On the other hand, the outer "ring" on the right side in today's APOD is very smooth. There are few or no really bright stars in it. Even so, it looks clearly blue.

Can this part of the Tadpole galaxy be blue at all? Yes, it can, because it could be dominated by stars similar to Sirius, Vega and Procyon. These stars are neither extremely bright nor extremely blue. They are, however, bluer than the Sun, and if the light from this part of the galaxy is dominated by Sirius-like stars, then it is okay to show it as bluish, in my opinion.

On the other hand, it is also possible that this part of the Tadpole Galaxy is dominated by Sun-like stars. If that is the case, then the blue color is not okay.

The center of the Tadpole Galaxy is seen as very faintly yellowish. We have every reason to believe that this part of the galaxy is redder than the Sun. But it looks hardly yellow at all.

To summarize, the blue parts of the Tadpole Galaxy look very blue, while the reddish parts of the galaxy look barely yellow at all. So the color balance of this picture is definitely very blue.

Ann

Chris Peterson · Post by **Chris Peterson** » Tue Dec 11, 2018 6:09 am

Karthik wrote: ↑Tue Dec 11, 2018 5:23 am This one is bluer than previous images from the same source (Hubble Legacy Archive)

https://apod.nasa.gov/apod/ap121108.html
https://apod.nasa.gov/apod/ap140825.html

Wonder why that is and which of these depict the true colour(s) of the Tadpole.

The concept of "true color" is very nebulous in astronomical images. The only true color of this object is what you'd see through a telescope: gray. Any long exposure image through filters is at best an approximation of what we might see if our eyes had greater sensitivity. This is especially true for images made from Hubble data, as such data is almost always collected through filters that map to a significantly different gamut than our eyes.

IMO, the best processed image of the three is the 2014 one. The star colors seem most accurate, and the lower saturation and flatter dynamic range make it easier for me to see detail and structure.

Ann · Post by **Ann** » Tue Dec 11, 2018 6:46 am

Chris Peterson wrote: ↑Tue Dec 11, 2018 6:09 am
Karthik wrote: ↑Tue Dec 11, 2018 5:23 am This one is bluer than previous images from the same source (Hubble Legacy Archive)

https://apod.nasa.gov/apod/ap121108.html
https://apod.nasa.gov/apod/ap140825.html

Wonder why that is and which of these depict the true colour(s) of the Tadpole.
IMO, the best processed image of the three is the 2014 one. The star colors seem most accurate, and the lower saturation and flatter dynamic range make it easier for me to see detail and structure.

I agree.

Ann

HellCat · Post by **HellCat** » Tue Dec 11, 2018 3:08 pm

Also agree with Chris and Ann about these colors relative to 2014-08-25.

As a writer, I also like the text from 2014 as well.
In today's caption, we have an incomplete phrase:
"The intruder galaxy itself, estimated to lie about 300 thousand light-years behind the, can..."

Steve

PS - I still think inserting an English major into the production loop wouldn't hurt.

Devil Particle · Post by **Devil Particle** » Tue Dec 11, 2018 3:16 pm

If you click on the link, "cosmic tadpole is", it directs you to this site: http://hubblesite.org/image/1181/news_release/2002-11

I am guessing the answer to my question is probably "both" or "neither". But the image on the hubblesite.org website is mirrored in relation to the APOD picture.

So, which orientation is correct?

Fred the Cat · Post by **Fred the Cat** » Tue Dec 11, 2018 3:23 pm

The first thing to come to mind seeing today's image was a song. Guess Who's

Click to play embedded YouTube video.

ems57fcva · Post by **ems57fcva** » Tue Dec 11, 2018 3:40 pm

Maybe this is a silly theory, but I see a long star trail here, and it looks like that far end of the tail is more blue than the near end.

I am wondering if there may not have been a pair of small galaxies like the Magellanic Clouds that hit Arp 188. One went behind and on up and its the identified "intruder". But the other one did a glancing blow, drew off a bunch of stars and gas from the main galaxy and them pulled it along to form the tail. The remnants of the second galaxy would be the bright areas on the side of the main tail. (If they were clusters formed out of the tail, they would be embedded in the tail.)

Just my two cents, but that tail is just too dramatic to be created by a lone small intruder galaxy in my opinion.

MarkBour · Post by **MarkBour** » Tue Dec 11, 2018 8:48 pm

HellCat wrote: ↑Tue Dec 11, 2018 3:08 pm As a writer, I also like the text from 2014 as well.
In today's caption, we have an incomplete phrase:
"The intruder galaxy itself, estimated to lie about 300 thousand light-years behind the, can..."

Steve

PS - I still think inserting an English major into the production loop wouldn't hurt.

... or maybe just be more careful when cutting, editing, and pasting. (But who among us never makes such mistakes?)
I note this caption, more or less the same for all three of these APODs, is closely related to the second paragraph of the Wikipedia article on the Tadpole Galaxy:

https://en.wikipedia.org/wiki/Tadpole_Galaxy
It is hypothesized that a more compact intruder galaxy crossed in front of the Tadpole Galaxy—from left to right from the perspective of Earth—and was slung around behind the Tadpole by their mutual gravitational attraction. During this close encounter, tidal forces drew out the spiral galaxy's stars, gas, and dust, forming the conspicuous tail. The intruder galaxy itself, estimated to lie about 300 thousand light-years behind the Tadpole, can be seen through foreground spiral arms at the upper left. Following its terrestrial namesake, the Tadpole Galaxy will likely lose its tail as it grows older, the tail's star clusters forming smaller satellites of the large spiral galaxy.

MarkBour · Post by **MarkBour** » Tue Dec 11, 2018 9:32 pm

Everyone seems to be favoring the 2014 version. I won't vote, but I have a comparison question. I find the 2012 version quite bright and colorful compared to the other two. It also is the one that most clearly seems to show more extended star features for the Tadpole and friends.

As I look at the 2012 version in particular, I see the 3 extended arms of stars labeled in the rough sketch at the right:

Of course arm "1" is the one that is mainly discussed in the APOD caption etc.
I find arm "2" quite interesting, though. It goes for a ways and steadily fades in brightness until it seems to have ended.
Finally, there is clearly an interesting arm coming out of the bright spiral galaxy at the bottom of the picture (I'm no good at finding galaxy names ... it might possibly be "FBB 2003".) It is distinctive and slightly curved at the far end. That all reminds me of a toadstool or mushroom.

Much fainter, possibly just imagined, there could be a connection running all the way between (2) and (3). I'm wondering if that is really there, or if I am just squinting too hard and seeing something that does not exist.

(That's my question ... anyone else see it ... or not? Or can anyone offer a more definitive way to decide such a question?)

Ann · Post by **Ann** » Tue Dec 11, 2018 11:12 pm

MarkBour wrote: ↑Tue Dec 11, 2018 9:32 pm Everyone seems to be favoring the 2014 version. I won't vote, but I have a comparison question. I find the 2012 version quite bright and colorful compared to the other two. It also is the one that most clearly seems to show more extended star features for the Tadpole and friends.
Capture.JPG
As I look at the 2012 version in particular, I see the 3 extended arms of stars labeled in the rough sketch at the right:

Of course arm "1" is the one that is mainly discussed in the APOD caption etc.

I find arm "2" quite interesting, though. It goes for a ways and steadily fades in brightness until it seems to have ended.

Finally, there is clearly an interesting arm coming out of the bright spiral galaxy at the bottom of the picture (I'm no good at finding galaxy names ... it might possibly be "FBB 2003".) It is distinctive and slightly curved at the far end. That all reminds me of a toadstool or mushroom.

Much fainter, possibly just imagined, there could be a connection running all the way between (2) and (3). I'm wondering if that is really there, or if I am just squinting too hard and seeing something that does not exist.

(That's my question ... anyone else see it ... or not? Or can anyone offer a more definitive way to decide such a question?)

Lovely drawing, Mark.

I don't see the connection between features 2 and 3, but in my mind's eye I seem to remember that I, too, just might have glimpsed it in the 2012 version.

A good thing about the skewed color balance of the 2018 version, whoever, is that the short arm segment number 2 looks bluish, while the tidal feature(?) coming out of the background galaxy does not. Based on color alone, I'd say that these two features are not connected.

Ann

Boomer12k · Post by **Boomer12k** » Wed Dec 12, 2018 2:43 am

Very nice...

:---[===] *

ems57fcva · Post by **ems57fcva** » Wed Dec 12, 2018 4:32 am

MarkBour wrote: ↑Tue Dec 11, 2018 9:32 pm Much fainter, possibly just imagined, there could be a connection running all the way between (2) and (3). I'm wondering if that is really there, or if I am just squinting too hard and seeing something that does not exist.

(That's my question ... anyone else see it ... or not? Or can anyone offer a more definitive way to decide such a question?)

That is an easy mistake to make. There is no bridge. Galaxy (3) looks to me to be a comparably-sized galaxy that is about twice as far away. In that case, it is about 400 million light-years behind the Tadpole Galaxy.

MarkBour · Post by **MarkBour** » Wed Dec 12, 2018 6:19 pm

Ann wrote: ↑Tue Dec 11, 2018 11:12 pm A good thing about the skewed color balance of the 2018 version, whoever, is that the short arm segment number 2 looks bluish, while the tidal feature(?) coming out of the background galaxy does not. Based on color alone, I'd say that these two features are not connected.

Ann

ems57fcva wrote: ↑Wed Dec 12, 2018 4:32 am That is an easy mistake to make. There is no bridge. Galaxy (3) looks to me to be a comparably-sized galaxy that is about twice as far away. In that case, it is about 400 million light-years behind the Tadpole Galaxy.

Thank you both. I can see that both pieces of evidence can help dispel the notion.

I guess one thing that remains, for me, is that the disruption of that more distant galaxy (which I described as a "toadstool stem" shape) looks pretty interesting in its own right.

Starship Asterisk*