Arp 78

[wimvb]

This galaxy, ngc 772 in the new general catalogue, has number 78 in Arp's catalogue of peculiar galaxies. It is located at a distance of approximately 130 Mly in the constellation Aries. The galaxy is surrounded by numerous smaller galaxies, notably ngc 770, just below the main target in this image. There is a gravitational tug of war going on between several of these galaxies, which has left its mark on ngc 772, giving it it's lopsided shape as well as a tidal stream. The brightest knots in this stream are barely visible in a superstretched version of the luminance data. A hint of the tail is just about visible below ngc 770.

Technical details:

Telescope: Skywatcher MN190 on a SW AZ-EQ6 mount

Camera: ZWO ASI294MM with Optolong LRGB filters

Exposures: L 76 x 2 minutes (152 minutes), RGB 20 x 4 minutes per channel (240 minutes). Total integration time: 6.5 hours

Processed in PixInsight.

The image could well do with double the integration time. Most of the data was collected under a bright moon earlier this month. Because of this especially the luminance data is weak and quite noisy. If the weather plays nice, I will try to double the amount of data on this target.

Annotated version (with two quasars indicated)

As always: click on the image to get to a larger version.

[Ceph]

Looks like a galaxy that are in heavy work.
Is it depending on the the black hole in the middle not being so strong thus throwing the stars and planets into eternety (not likely) or ngc 772 just ate another galaxy and is finishing the meal?

The angle and appearence of the galaxy makes me wonder

 

[wimvb]

The smaller galaxies around it can have a stronger gravitational pull on the arms of ngc 772 than its own mass has. This is just a result of who is closest, not necessarily who is heavier. It moves matter from ngc 772 to those other galaxies. I haven't checked it any further, but this is one of two possible scenarios. It is also possible that what we see here is ngc 772 pulling in matter from smaller ngc 770. Whoever is being pulled apart, this is similar to what will happen with our own Milky Way and the Andromeda galaxy several billion years into the future. Eventually, after millions of years, this galactic dance will result in a full merger of the galaxies involved.

[ItsmeMaw]

When I see a galaxy surrounded by more distant galaxies, the only thing I can think is wow!

Wonderful image! Thanks.

[Allinthehead]

Great image Wim, you've managed to get lovely colour in the stars. Any tips for this?

[wimvb]

Thanks. I use arcsinh stretch on the rgb data and scale the stretched L down to 0.9 - 0.95, ie the brightest stars have a value no higher than this. If luminance is at 100% somewhere, that part of the image will be pure white after lrgb combination. So I avoid that by scaling L.

[peter shah]

Beautifully processed

[gorann]

Great image Wim! From an aesthetical point of view I think this galaxy is just messed up enough, but not too much, by gravitational forces to make it stand out.

CS (whenever that may happen)

Göran

[wimvb]

3 hours ago, peter shah said:

Beautifully processed

Thank you, Peter.

3 hours ago, gorann said:

Great image Wim! From an aesthetical point of view I think this galaxy is just messed up enough, but not too much, by gravitational forces to make it stand out.

CS (whenever that may happen)

Göran

Thanks, Göran. I have another image in the pipeline: ngc 7771 which is a pair of galaxies messing up each other. So far I have collected about 4 hours of RGB data, and a shell structure is just starting to show. It needs a lot more data before it is presentable, so hopefully those clear skies will come with the waning moon. (One can always hope.)

Cheers,

[tomato]

That’s a great galaxy image, so much to look at in the frame. 

[GalaxyGael]

Lovely Wim, the Arp catalog is a favourite if they high enough in the sky. Nice approach on the arcsinh stretch. 

Incidentally, I have a bundle of arcsinh stretch preset curves for PS if anyone reading this wants them, with various degrees form 10-1000.

NGC 474 and friends are accessible too I think, what galaxy(ies) are you imaging now?

Edited October 26, 2021 by GalaxyGael

[wimvb]

3 hours ago, GalaxyGael said:

NGC 474 and friends are accessible too I think, what galaxy(ies) are you imaging now?

Atm ngc 7771, a galaxy group with a weak shell structure much like ngc 474. Ngc474 is a bit low in the sky for me, but looks very interesting.

[GalaxyGael]

It does indeed, must add it to the list for the longer fl scope. There is a nice cluster around 1 Ari (a bit higher than Sheraton star)  that is a little higher up that the Fiddlehead galaxy from your post above. Nice cluster too with various galaxy types.

Edited October 26, 2021 by GalaxyGael

[wimvb]

51 minutes ago, GalaxyGael said:

There is a nice cluster around 1 Ari (a bit higher than Sheraton star)

Do you have an ngc number for that? (If I google Sheraton star I get completely irrelevant information. Weird. 😉😋 )

[GalaxyGael]

There's a bunch together, including

NGC 697, 678, 680, 694, 691, and IC 167 etc.

[wimvb]

That is a very nice group