APOD: Arp 78: Peculiar Galaxy in Aries (2022 Mar 24)

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APOD: Arp 78: Peculiar Galaxy in Aries (2022 Mar 24)

Post by APOD Robot » Thu Mar 24, 2022 4:05 am

Image Arp 78: Peculiar Galaxy in Aries

Explanation: Peculiar spiral galaxy Arp 78 is found within the boundaries of the head strong constellation Aries. Some 100 million light-years beyond the stars and nebulae of our Milky Way galaxy, the island universe is over 100,000 light-years across. Also known as NGC 772, it sports a prominent, outer spiral arm in this detailed cosmic portrait from the large Gemini North telescope near the summit of Maunakea, Hawaii, planet Earth. Tracking along sweeping dust lanes and lined with young blue star clusters, Arp 78's spiral arm is likely pumped-up by galactic-scale gravitational tidal interactions The close companion galaxy responsible is NGC 770, located off the upper right of this frame. But more distant background galaxies are clearly visible in the cosmic field of view.

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Re: APOD: Arp 78: Peculiar Galaxy in Aries (2022 Mar 24)

Post by Ann » Thu Mar 24, 2022 5:31 am

NGC 772 and NGC 770 Jim Thommes.png
NGC 772 with its small companion galaxy, NGC 770. Interactions with NGC 770
is likely what gives NGC 772 its strange shape. Image: Jim Thommes.

Today's APOD is a beautiful image. Please note the wealth of small background galaxies, which have been redshift-reddened to orange and reddish hues. It is likely that the reddest background galaxies are the most distant ones, but it is not quite certain, because a galaxy with an intrinsic old yellow population will look redder than a young starforming one at the same distance.

Note the yellow-white galaxy in the upper left corner, and the galaxy with the blue arms to the right of it. These two galaxies could be at the same distance, and they could be physically close to one another and interacting. They are more distant than NGC 772, but not so much so that their colors are strongly affected, given the filters that were used for this image (and the processing of the image). The largest yellow-white galaxy near bottom of the image could be at a comparable distance to the two at upper left.

Please note the blue star clusters that seem to be intermingled with the small red background galaxies, stretching all the way from left to right (or from right to left) in the lower part of the APOD. These blue clusters trace an outer arm of NGC 772.

NASA's now-defunct ultraviolet-detecting space telescope GALEX would have had a field day with NGC 772, making it look considerably larger at ultraviolet than at visible wavelengths due to the galaxy's ultraviolet-bright but visibly faint outer arm.

Take a look at galaxy NGC 1512 and its smaller companion NGC 1510 in visible and ultraviolet light to see what I mean by arms that suddenly pop into view at ultraviolet wavelengths:

Ann
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Re: APOD: Arp 78: Peculiar Galaxy in Aries (2022 Mar 24)

Post by orin stepanek » Thu Mar 24, 2022 11:25 am

Kinda looks stretched out a bit! In time, would it pull it's arm tighter to the main galaxy? :?
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Re: APOD: Arp 78: Peculiar Galaxy in Aries (2022 Mar 24)

Post by johnnydeep » Thu Mar 24, 2022 9:25 pm

Hmm, the text says that the small companion galaxy responsible for affecting the large spiral arm is located off the upper right of the frame. But Ann's posted pic would seem to put it in the upper left of the APOD image instead.
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Re: APOD: Arp 78: Peculiar Galaxy in Aries (2022 Mar 24)

Post by bystander » Thu Mar 24, 2022 9:33 pm

johnnydeep wrote: Thu Mar 24, 2022 9:25 pm Hmm, the text says that the small companion galaxy responsible for affecting the large spiral arm is located off the upper right of the frame. But Ann's posted pic would seem to put it in the upper left of the APOD image instead.
Maybe upper center.
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Re: APOD: Arp 78: Peculiar Galaxy in Aries (2022 Mar 24)

Post by Ann » Fri Mar 25, 2022 5:19 am

johnnydeep wrote: Thu Mar 24, 2022 9:25 pm Hmm, the text says that the small companion galaxy responsible for affecting the large spiral arm is located off the upper right of the frame. But Ann's posted pic would seem to put it in the upper left of the APOD image instead.
Note that the thick arm system of NGC 772 is seen curving "below" the center of the galaxy in the APOD, but "above" the center of the galaxy in Jim Thommes' image. If you turn Jim Thommes' image around 180 degrees, NGC 772 will be oriented the same way as in the APOD, and NGC 770 will indeed be seen to the upper right of NGC 772.

I suspect that it is in Jim Thommes' image that north is up, as convention dictates. Note that Simbad's astronomical database shows us NGC 772 with its arm system "above" the galaxy's nucleus, just like Jim Thommes' image does.

Ann
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Re: APOD: Arp 78: Peculiar Galaxy in Aries (2022 Mar 24)

Post by johnnydeep » Fri Mar 25, 2022 2:55 pm

Ann wrote: Fri Mar 25, 2022 5:19 am
johnnydeep wrote: Thu Mar 24, 2022 9:25 pm Hmm, the text says that the small companion galaxy responsible for affecting the large spiral arm is located off the upper right of the frame. But Ann's posted pic would seem to put it in the upper left of the APOD image instead.
Note that the thick arm system of NGC 772 is seen curving "below" the center of the galaxy in the APOD, but "above" the center of the galaxy in Jim Thommes' image. If you turn Jim Thommes' image around 180 degrees, NGC 772 will be oriented the same way as in the APOD, and NGC 770 will indeed be seen to the upper right of NGC 772.

I suspect that it is in Jim Thommes' image that north is up, as convention dictates. Note that Simbad's astronomical database shows us NGC 772 with its arm system "above" the galaxy's nucleus, just like Jim Thommes' image does.

Ann
I still think "upper left" is way more accurate than "upper right" for the location of the small companion galaxy:

NGC 722 Companion.JPG
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Re: APOD: Arp 78: Peculiar Galaxy in Aries (2022 Mar 24)

Post by Ann » Fri Mar 25, 2022 3:52 pm

johnnydeep wrote: Fri Mar 25, 2022 2:55 pm
Ann wrote: Fri Mar 25, 2022 5:19 am
johnnydeep wrote: Thu Mar 24, 2022 9:25 pm Hmm, the text says that the small companion galaxy responsible for affecting the large spiral arm is located off the upper right of the frame. But Ann's posted pic would seem to put it in the upper left of the APOD image instead.
Note that the thick arm system of NGC 772 is seen curving "below" the center of the galaxy in the APOD, but "above" the center of the galaxy in Jim Thommes' image. If you turn Jim Thommes' image around 180 degrees, NGC 772 will be oriented the same way as in the APOD, and NGC 770 will indeed be seen to the upper right of NGC 772.

I suspect that it is in Jim Thommes' image that north is up, as convention dictates. Note that Simbad's astronomical database shows us NGC 772 with its arm system "above" the galaxy's nucleus, just like Jim Thommes' image does.

Ann
I still think "upper left" is way more accurate than "upper right" for the location of the small companion galaxy:

You're right, Johnny!

Ann
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