Starship Asterisk*

Unraveling NGC 3169

Explanation: Spiral galaxy NGC 3169 looks to be unraveling like a ball of cosmic yarn. It lies some 70 million light-years away, south of bright star Regulus toward the faint constellation Sextans. Wound up spiral arms are pulled out into sweeping tidal tails as NGC 3169 (left) and neighboring NGC 3166 interact gravitationally. Eventually the galaxies will merge into one, a common fate even for bright galaxies in the local universe. Drawn out stellar arcs and plumes are clear indications of the ongoing gravitational interactions across the deep and colorful galaxy group photo. The telescopic frame spans about 20 arc minutes or about 400,000 light-years at the group's estimated distance, and includes smaller, bluish NGC 3165 to the right. NGC 3169 is also known to shine across the spectrum from radio to X-rays, harboring an active galactic nucleus that is the site of a supermassive black hole.

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NGC 3169 and NGC 3166 are indeed an interesting pair of galaxies! They used to be normal spiral galaxies for sure, but now one of them (NGC 3169) is indeed "unraveling", and the other one is in the process of losing its spiral galaxy characteristics altogether.


You have to look at this "inverted light" picture of NGC 3169 and NGC 3166 by Mark Hanson and Martin Pugh, which really brings out the "contours" of NGC 3169 and NGC 3166!


NGC 3169 and NGC 3166 are very close to one another. They have undoubtedly been interacting for a long time, chafing away at one another, disturbing each other's cold molecular clouds, upsetting one another's dust lanes and eating away at each other's abilities to form new stars. NGC 3169 still contains streaks of blue and even a few pink emission nebulas, but its sites of star formation have been drastically reduced. And NGC 3166 has no obvious sites of star formation at all, although it does have a ring of relatively young stars around its nucleus. And a strange bluish "jet" appears to emerge from it, pointing down and to the left!


The picture above is a GALEX ultraviolet image, where blue means light from hot stars of spectral classes A-O, and yellow means light from cool stars of spectral classes F-M. (Well, roughly.)

You can see the blue arms of NGC 3169. You can also see a small, faintly bluish ring around the core of NGC 3166, while the disk of NGC 3166 is faint and all yellow. But do note the bluish "jet" that seems to emerge from NGC 3166, pointing down and to the left. According to this site, both NGC 3169 and NGC 3166 have active black holes, and I have to wonder if the jet-like feature emerging from NGC 3166 is a remnant of an outburst of that galaxy's black hole.

The supermassive black hole of giant elliptical galaxy M87 produces just such a bluish jet, although we should not pretend that the black hole of NGC 3166 is in any way comparable to the monster black hole in M87! We don't even know if that jet-like thing seemingly emerging from NGC 3166 is a jet in the first place, or, if so, if it has anything to do with the black hole of NGC 3166. Meanwhile, let's enjoy the jet of M87!

Ann

So, I'm reading that tiny NGC 3165 is also part of this triple, and at about the same distance, yet it doesn't seem to be interacting with the other two at all, either currently or in the past. Why not? Also, I note that NGC 3165 is classified as a spiral too, which would confirm that spirals really do come in a wide range of sizes!

PS - This seems to be a virtual repeat of https://apod.nasa.gov/apod/ap230302.html from only two months ago.

johnnydeep wrote: ↑Thu May 23, 2024 6:43 pm So, I'm reading that tiny NGC 3165 is also part of this triple, and at about the same distance, yet it doesn't seem to be interacting with the other two at all, either currently or in the past. Why not? Also, I note that NGC 3165 is classified as a spiral too, which would confirm that spirals really do come in a wide range of sizes!

PS - This seems to be a virtual repeat of https://apod.nasa.gov/apod/ap230302.html from only two months ago.

Yes, it seems that NGC 3165 is also part of the trio, because all three galaxies have quite similar radial velocities. I do believe, however, that NGC 3165 is a newcomer to the NGC 3169/NGC 3166 group, and that it hasn't undergone a lot of gravitational chafing and bullying from the two large galaxies, because if it had, it wouldn't be as blue as it is. Compare NGC 3165 with the two yellow satellites of Andromeda, M32 and NGC 205, which have undoubtedly orbited Andromeda for a long time.


As for the Hubble classification of NGC 3165, I believe that it is Sm, or midway between a spiral and an irregular galaxy.

Ann

johnnydeep wrote: ↑Thu May 23, 2024 6:43 pm So, I'm reading that tiny NGC 3165 is also part of this triple, and at about the same distance, yet it doesn't seem to be interacting with the other two at all, either currently or in the past. Why not?

First, these interactions are tidal. That means they occur when extended bodies are close enough together that the gravitational force where they are nearest to each other is significantly different from the force on the parts that are farthest apart. The smaller galaxy (in its current position) is almost a point mass compared with the others.

Second, we aren't looking a a static arrangement here. The bodies are in a complex and always changing trinary orbit around each other. The small body may not get very close to the others.

Third, we really need to see the motion over time. The two apparently interacting galaxies may or may not be interacting strongly as we see them here. They may have been closer millions of years ago, and much of the interaction is reduced now, with us just seeing the aftermath and the tidal tails.

Ann wrote: ↑Thu May 23, 2024 7:14 pm

johnnydeep wrote: ↑Thu May 23, 2024 6:43 pm So, I'm reading that tiny NGC 3165 is also part of this triple, and at about the same distance, yet it doesn't seem to be interacting with the other two at all, either currently or in the past. Why not? Also, I note that NGC 3165 is classified as a spiral too, which would confirm that spirals really do come in a wide range of sizes!

PS - This seems to be a virtual repeat of https://apod.nasa.gov/apod/ap230302.html from only two months ago.

Yes, it seems that NGC 3165 is also part of the trio, because all three galaxies have quite similar radial velocities. I do believe, however, that NGC 3165 is a newcomer to the NGC 3169/NGC 3166 group, and that it hasn't undergone a lot of gravitational chafing and bullying from the two large galaxies, because if it had, it wouldn't be as blue as it is. Compare NGC 3165 with the two yellow satellites of Andromeda, M32 and NGC 205, which have undoubtedly orbited Andromeda for a long time.

...

As for the Hubble classification of NGC 3165, I believe that it is Sm, or midway between a spiral and an irregular galaxy.

Ann

Yeah, it's not much of a spiral after all it seems.

Chris Peterson wrote: ↑Thu May 23, 2024 7:25 pm

johnnydeep wrote: ↑Thu May 23, 2024 6:43 pm So, I'm reading that tiny NGC 3165 is also part of this triple, and at about the same distance, yet it doesn't seem to be interacting with the other two at all, either currently or in the past. Why not?

First, these interactions are tidal. That means they occur when extended bodies are close enough together that the gravitational force where they are nearest to each other is significantly different from the force on the parts that are farthest apart. The smaller galaxy (in its current position) is almost a point mass compared with the others.

Second, we aren't looking a a static arrangement here. The bodies are in a complex and always changing trinary orbit around each other. The small body may not get very close to the others.

Third, we really need to see the motion over time. The two apparently interacting galaxies may or may not be interacting strongly as we see them here. They may have been closer millions of years ago, and much of the interaction is reduced now, with us just seeing the aftermath and the tidal tails.

Ann wrote: ↑Thu May 23, 2024 7:16 am
[...]
According to this site, both NGC 3169 and NGC 3166 have active black holes, and I have to wonder if the jet-like feature emerging from NGC 3166 is a remnant of an outburst of that galaxy's black hole.
[...]

Ann

I think that the "jet" of NGC 3166 is an arm of NGC 3169 that was stretched towards NGC 3166 by tidal action. In GALEX's UV, "the face" of the galaxy appears to be looking to the bottom left. In the optical, however, to the top right. If the inner core region (yellow in the UV) has effectively rotated 180 degrees, this could help explain the chaotic appearance of the galaxy.

... and i like the hubble close up of the core of NGC3169...
jac berne (flickr)

This galaxy looks very unique to me. I am a student of galaxies, these look brand new to me.
There appear to be ~3 rings around NGC 3169 perpendicular to its plane of rotation. Has the other galaxy circled it that many times? I would love to see the simulation of these 2 galaxies interacting.
Note, I was working as an astrophysicist 1972-1974 at MIT CSR in the OSO-7 X-ray Astronomy group, during which time the Toomre brothers were doing the 1st computer simulations of galaxies interacting.

ChrisHeinz wrote: ↑Fri May 24, 2024 4:00 am This galaxy looks very unique to me. I am a student of galaxies, these look brand new to me.
There appear to be ~3 rings around NGC 3169 perpendicular to its plane of rotation. Has the other galaxy circled it that many times? I would love to see the simulation of these 2 galaxies interacting.
Note, I was working as an astrophysicist 1972-1974 at MIT CSR in the OSO-7 X-ray Astronomy group, during which time the Toomre brothers were doing the 1st computer simulations of galaxies interacting.

It is very interesting that you have worked close to the Toomre brothers when they were doing the first computer simulations of galactic interactions!

As for NGC 3169, I agree that it looks unique. The fact that its arms seem to have lifted above and below its own main orbital plane and left structures behind is something I can't remember having seen before.

However, I want you to consider this group of galaxies:


NGC 474 is an extreme shell galaxy due to interactions with the small blue ring galaxy, NGC 470, which itself appears to be relatively undisturbed by the tidal dancing. Yes, but look at galaxy NGC 467 at upper left. It, too, is a very disturbed shell galaxy, similar in size and overall properties to NGC 474. But according to the radial velocities of these three galaxies, NGC 467 is two and a half times as far away as the other two and totally unaffected by their presence!!!

Is that even possible? Or has NGC 467 received a "kick" that has made it move away from NGC 474 and NGC 470 at breakneck speed?

Ann

johnnydeep wrote: ↑Thu May 23, 2024 6:43 pm So, I'm reading that tiny NGC 3165 is also part of this triple, and at about the same distance, yet it doesn't seem to be interacting with the other two at all, either currently or in the past. Why not? Also, I note that NGC 3165 is classified as a spiral too, which would confirm that spirals really do come in a wide range of sizes!

PS - This seems to be a virtual repeat of https://apod.nasa.gov/apod/ap230302.html from only two months ago.

So. It seems that this "family portrait" of galaxies has fascinated several top astrophotographers over time.
I think it's great that APOD is honoring these - so it doesn't bother me that the text has remained the same over time.


APOD 2024 May 23 Image Credit & Copyright: Christophe Vergnes, Aziz Kaeouach
APOD 2023 March 2 Image Credit & Copyright: Mike Selby & Mark Hanson



APOD 2015 November 6 Image Credit & Copyright: Warren Keller, Steve Mazlin, Jack Harvey, Steve Menaker (SSRO/ UNC/PROMPT/ CTIO)
APOD 2013 March 28 Image Credit & Copyright: Adam Block, Mt. Lemmon SkyCenter, University of Arizona

Ann wrote: ↑Fri May 24, 2024 4:54 am

ChrisHeinz wrote: ↑Fri May 24, 2024 4:00 am This galaxy looks very unique to me. I am a student of galaxies, these look brand new to me.
There appear to be ~3 rings around NGC 3169 perpendicular to its plane of rotation. Has the other galaxy circled it that many times? I would love to see the simulation of these 2 galaxies interacting.
Note, I was working as an astrophysicist 1972-1974 at MIT CSR in the OSO-7 X-ray Astronomy group, during which time the Toomre brothers were doing the 1st computer simulations of galaxies interacting.

It is very interesting that you have worked close to the Toomre brothers when they were doing the first computer simulations of galactic interactions!

As for NGC 3169, I agree that it looks unique. The fact that its arms seem to have lifted above and below its own main orbital plane and left structures behind is something I can't remember having seen before.

However, I want you to consider this group of galaxies:

NGC 474 NGC 470 NGC 467 Mark Hanson S Mazlin W Keller et al.png

NGC 474 (center right), NGC 470 (small ring galaxy) and NGC 467 (upper left).
Credit: Mark Hanson, S. Mazlin, W. Keller, R. Parker, T. Tse, P. Proulx, D. Plesko;
SSRO/PROMPT/CTIO

NGC 474 is an extreme shell galaxy due to interactions with the small blue ring galaxy, NGC 470, which itself appears to be relatively undisturbed by the tidal dancing. Yes, but look at galaxy NGC 467 at upper left. It, too, is a very disturbed shell galaxy, similar in size and overall properties to NGC 474. But according to the radial velocities of these three galaxies, NGC 467 is two and a half times as far away as the other two and totally unaffected by their presence!!!

Is that even possible? Or has NGC 467 received a "kick" that has made it move away from NGC 474 and NGC 470 at breakneck speed?

Ann

If NGC 467 is two and a half times as far away as the other two, it would have to be huge in size. However, I doubt that. I would rather assume that it has in reality a similar size to NGC 474.