APOD: NGC 1316: After Galaxies Collide (2015 Sep 09)

[APOD Robot]

NGC 1316: After Galaxies Collide

Explanation: Astronomers turn detectives when trying to figure out the cause of startling sights like NGC 1316. Their investigation indicates that NGC 1316 is an enormous elliptical galaxy that started, about 100 million years ago, to devour a smaller spiral galaxy neighbor, NGC 1317, just above it. Supporting evidence includes the dark dust lanes characteristic of a spiral galaxy, and faint swirls and shells of stars and gas visible in this wide and deep image. One thing that remains unexplained is the unusually small globular star clusters, seen as faint dots on the image. Most elliptical galaxies have more and brighter globular clusters than NGC 1316. Yet the observed globulars are too old to have been created by the recent spiral collision. One hypothesis is that these globulars survive from an even earlier galaxy that was subsumed into NGC 1316. Another surprising attribute of NGC 1316, also known as Fornax A, is its giant lobes of gas that glow brightly in radio waves.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

[Ann]

APOD robot wrote:
Their investigation indicates that NGC 1316 is an enormous elliptical galaxy that started, about 100 million years ago, to devour a smaller spiral galaxy neighbor, NGC 1317, just above it.

That's interesting. NGC 1317 looks rather undisturbed. I would have thought that the distorted outer layers of NGC 1316, as well as the strange and misshapen dust lanes in its inner bulge, indicated a previous merger that NGC 1316 had undergone with another small and probably spiral galaxy. That other small galaxy would now have been completely devoured, leaving only the chaotic tidal streamers and strange inner dust lanes of NGC 1316 as testimony to what had happened.

As I noted during a discussion of an APOD featuring the Andromeda galaxy, NGC 1316 is very slightly bluer than Andromeda overall. To me this suggests a recent, but not too recent, merger involving NGC 1316.

One thing that remains unexplained is the unusually small globular star clusters, seen as faint dots on the image. Most elliptical galaxies have more and brighter globular clusters than NGC 1316. Yet the observed globulars are too old to have been created by the recent spiral collision. One hypothesis is that these globulars survive from an even earlier galaxy that was subsumed into NGC 1316.

Indeed. That, too, suggests that NGC 1316 has undergone a merger some time ago, perhaps two billion years ago or so. It also suggests that the history of NGC 1316 previous to the merger that left the small globulars, the chaotic tidal streamers and the shredded inner dust lanes behind, was a peaceful one. The elliptical galaxies that are chock full of bright globulars have likely had a violent history with lots of giant mergers.

Ann

[Boomer12k]

"After Galaxies Collide"....you hope your Solar System stays in the galaxy and not flung way out into intergalactic space. Well...OK...it MIGHT, if possible, be good from an Astronomy point of view to be way out there, and look at a galaxy from an angle that has a good view, lots to study and wonder about.

IF they had a smooth merger...WHAT does that say about the Milky Way Galaxy? 150 Globulars? Would that not mean lots of mergers? Not if they formed WITH the galaxy....

I wonder what that would do to Asteroid Belts, and planets in a solar system? If flung out so far:?:

Since Globulars formed Generally at or before the galaxy proper, I thought it was understood their intense gravity and density held them together...I guess even through mergers. Though some stars might be siphoned off?

:---[===] *

[starsurfer]

This is a great image of a very dramatic and dynamic peculiar galaxy that is actually featured in the Arp Atlas of Peculiar Galaxies as Arp 154 and is also in the Arp-Madore catalogue as well. It's nice to see a shell elliptical featured on APOD, the small companion NGC 1317 is also a shell elliptical. The tidal features of NGC 1316 extend for even wider than the extent of this picture! The shell elliptical I most want to see photographed in detail by an amateur is NGC 3923 in Hydra. Also to make Ann happy, here is a small list of some shell elliptical galaxies I like:

1. NGC 1210 by Steve Crouch
2. NGC 1344 by Don Goldman
3. NGC 2634 by Bob Franke

[Ann]

Boomer12k wrote:
IF they had a smooth merger...WHAT does that say about the Milky Way Galaxy? 150 Globulars? Would that not mean lots of mergers? Not if they formed WITH the galaxy....

My guess is that the Milky Way has only merged with small galaxies in a gentle way. I don't think we have had any major mergers at all, and nothing as dramatic as the merger that created the strange shape and dust lanes of NGC 1316.

I don't think 150 globulars is really a lot.

https://en.wikipedia.org/wiki/Messier_87#Components wrote:
M87 has an abnormally large population of globular clusters. A 2006 survey out to an angular distance of 25′ from its core estimates that there are 12,000 ± 800 globular clusters in orbit around M87, as compared to the Milky Way's 150–200.[64]

I, too, would dearly love exactly what caused all those ancient (~12 billion years old) globular clusters to form. But astronomers don't really know, I think. Clearly proto-Milky Way underwent some real upheavals during the era when most of its globulars formed, perhaps inside proto-Milky Way, as you said. But some of "our" globulars have certainly been stolen from small galaxies that have merged with the Milky Way.

Boomer 12k wrote:
Since Globulars formed Generally at or before the galaxy proper, I thought it was understood their intense gravity and density held them together...I guess even through mergers. Though some stars might be siphoned off?

Indeed, globulars are held together by their own gravity. But they keep losing individual members all the time, which are shot out into space during the continuous game of stellar pin-ball going on inside globular clusters. Low-mass stars are lost far easier than high-mass ones.

And I think you are quite right that any massive globular would survive almost any merger. After all, some globulars keep plunging right through the disk of the Milky Way, and they survive that dangerous dive again and again... though I think they tend to lose a couple of stars every time.

Ann

[Ron-Astro Pharmacist]

Almost reminds me of some other giant lobes also seen initially in radio waves. Any relationship?

And like sands through the hourglass, so are the days of our lives…

Love the link zooming in on today's APOD. Really gives one perspective on where these exist in the night sky!!

[BMAONE23]

I too noticed that the "Shells" extend well beyond the image. A deeper image of a larger area might show the Shells extending almost twice as far as indicated in this image

[Ann]

This is a great image of a very dramatic and dynamic peculiar galaxy that is actually featured in the Arp Atlas of Peculiar Galaxies as Arp 154 and is also in the Arp-Madore catalogue as well. It's nice to see a shell elliptical featured on APOD, the small companion NGC 1317 is also a shell elliptical. The tidal features of NGC 1316 extend for even wider than the extent of this picture! The shell elliptical I most want to see photographed in detail by an amateur is NGC 3923 in Hydra. Also to make Ann happy, here is a small list of some shell elliptical galaxies I like:

1. NGC 1210 by Steve Crouch
2. NGC 1344 by Don Goldman
3. NGC 2634 by Bob Franke

I forgot to thank you for that list, starsurfer! Bob Franke's image is amazing!

Ann

[starsurfer]

I too noticed that the "Shells" extend well beyond the image. A deeper image of a larger area might show the Shells extending almost twice as far as indicated in this image

This widefield image by Marco Lorenzi shows a faint tidal tail but the image isn't deep enough for the faintest features.

[starsurfer]

This is a great image of a very dramatic and dynamic peculiar galaxy that is actually featured in the Arp Atlas of Peculiar Galaxies as Arp 154 and is also in the Arp-Madore catalogue as well. It's nice to see a shell elliptical featured on APOD, the small companion NGC 1317 is also a shell elliptical. The tidal features of NGC 1316 extend for even wider than the extent of this picture! The shell elliptical I most want to see photographed in detail by an amateur is NGC 3923 in Hydra. Also to make Ann happy, here is a small list of some shell elliptical galaxies I like:

1. NGC 1210 by Steve Crouch
2. NGC 1344 by Don Goldman
3. NGC 2634 by Bob Franke

I forgot to thank you for that list, starsurfer! Bob Franke's image is amazing!

Ann

It is an amazing region, would love to see it imaged by Adam Block!