Starship Asterisk*

NGC 4651: The Umbrella Galaxy

Explanation: It's raining stars. What appears to be a giant cosmic umbrella is now known to be a tidal stream of stars stripped from a small satellite galaxy. The main galaxy, spiral galaxy NGC 4651, is about the size of our Milky Way, while its stellar parasol appears to extend some 100 thousand light-years above this galaxy's bright disk. A small galaxy was likely torn apart by repeated encounters as it swept back and forth on eccentric orbits through NGC 4651. The remaining stars will surely fall back and become part of a combined larger galaxy over the next few million years. The featured image was captured by the Canada-France-Hawaii Telescope (CFHT) in Hawaii, USA. The Umbrella Galaxy lies about 50 million light-years distant toward the well-groomed northern constellation Coma Berenices.

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The umbrella of NGC 4651 is indeed dramatic-looking. Today's APOD is very fine, but I prefer the APOD of July 2, 2014, which shows more clearly the "counter-jet" on the opposite side of the disk of NGC 4651. The APOD by R. J. GaBany et.al. also identifies the core of the small shredded satellite galaxy whose tidal remnants give NGC 4651 its umbrella-like shape. The "counter-tail" on the opposite side of NGC 4651 shows that the larger galaxy is also affected by the tidal forces that have torn the small satellite galaxy to shreds.

What about the outer arc, the "canopy" of the umbrella? It must be caused by the pile-up of material that has previously been shed by NGC 4651. But the way the "shaft" of the umbrella seems to stab the "canopy" of it makes it look as if the shaft of the umbrella was a jet emitted by a central black hole of NGC 4651. However, the soft smooth and intermediately-colored appearance of the "jet" clearly suggests that this is a stellar stream, made up of the sort of old metal-poor stars that we expect to find in a spheroidal dwarf galaxy, and not a violently emitted jet of ionized plasma that we expect from a black hole.

Another galaxy that displays a "jet" and an "arc" is NGC 3310, the Bow and Arrow Galaxy:


In the case of NGC 3310, the jet is clearly made up of young stars, which seem to have been flung out of the galaxy due to violent processes caused by a past merger. It seems likely (to me at least) that some of the young stars have formed "in situ" as a large helping of gas was flung out of the NGC 3310 galaxy proper.

Note that the "Bow" of NGC 3310 is made up of much older stars than the "Arrow", whereas in NGC 4651 the "Shaft" and the "Canopy" of the umbrella seem to be made up of the same sort of intermediate to old stars.

Note, too, that in NGC 3310 the "Arrow" seems to penetrate right through the "Bow", which, however, does not seem to feel "the pain of the arrow". Maybe the arrow is not "touching the bow". The arc-like structure of the bow could be a foreground object that partly hides the arrow.

Similarly, perhaps the shaft of the umbrella is unconnected to the canopy of it. Perhaps they are seen in silhouette and just seem to touch from our perspective.

Ann

Maybe NGC4651 is covered by Travelers!
Very interesting photo of star strem being sheered off by invader!
https://www.preventivevet.com/hubfs/how ... %20cat.png
gonna be a pretty kitty after grooming!

Any idea why the CFHT can't afford to get some Astrodon or Chroma filters that won't show halos on bright stars? If you've already spent millions on the scope and observatory, why skimp on poor quality filters?

APOD Robot wrote: ↑Mon Feb 07, 2022 5:05 am NGC 4651: The Umbrella Galaxy

Explanation: It's raining stars. What appears to be a giant cosmic umbrella is now known to be a tidal stream of stars stripped from a small satellite galaxy. The main galaxy, spiral galaxy NGC 4651, is about the size of our Milky Way, while its stellar parasol appears to extend some 100 thousand light-years above this galaxy's bright disk. A small galaxy was likely torn apart by repeated encounters as it swept back and forth on eccentric orbits through NGC 4651. The remaining stars will surely fall back and become part of a combined larger galaxy over the next few million years. The featured image was captured by the Canada-France-Hawaii Telescope (CFHT) in Hawaii, USA. The Umbrella Galaxy lies about 50 million light-years distant toward the well-groomed northern constellation Coma Berenices.

Very interesting "cannibal" galaxy, but I'm mighty disappointed that the linked-to Hubble pic doesn't show any part of the "umbrella" at all!

Since NGC 4561 is 50 million light years distant, and thus as seen 50 million light years ago, can we assume that the integration of the two galaxies has taken place?

DL MARTIN wrote: ↑Mon Feb 07, 2022 5:44 pm
Since NGC 4561 is 50 million light years distant, and thus as seen 50 million light years ago, can we assume that the integration of the two galaxies has taken place?

NO. Galactic collision relaxation times would probably be on the order of a few billion years.

DL MARTIN wrote: ↑Mon Feb 07, 2022 5:44 pm Since NGC 4561 is 50 million light years distant, and thus as seen 50 million light years ago, can we assume that the integration of the two galaxies has taken place?

If we view it again in 50 million years it will scarcely look different.

Chris Peterson wrote: ↑Mon Feb 07, 2022 7:16 pm

DL MARTIN wrote: ↑Mon Feb 07, 2022 5:44 pm Since NGC 4561 is 50 million light years distant, and thus as seen 50 million light years ago, can we assume that the integration of the two galaxies has taken place?

If we view it again in 50 million years it will scarcely look different.

But wait! This sentence in the APOD description seems to be at odds with that:

A small galaxy was likely torn apart by repeated encounters as it swept back and forth on eccentric orbits through NGC 4651. The remaining stars will surely fall back and become part of a combined larger galaxy over the next few million years.

Note the use of the past tense "was", the seeming absence of the smaller galaxy (except for the "small core" as shown by Ann), and the apparent timeline of only a few million years before we have a "combined larger galaxy", implying the merger would be done by then. What am I missing?

But I did find the stated short timeline pretty unusual if true.

johnnydeep wrote: ↑Mon Feb 07, 2022 7:51 pm

Chris Peterson wrote: ↑Mon Feb 07, 2022 7:16 pm

DL MARTIN wrote: ↑Mon Feb 07, 2022 5:44 pm Since NGC 4561 is 50 million light years distant, and thus as seen 50 million light years ago, can we assume that the integration of the two galaxies has taken place?

If we view it again in 50 million years it will scarcely look different.

But wait! This sentence in the APOD description seems to be at odds with that:

A small galaxy was likely torn apart by repeated encounters as it swept back and forth on eccentric orbits through NGC 4651. The remaining stars will surely fall back and become part of a combined larger galaxy over the next few million years.

Note the use of the past tense "was", the seeming absence of the smaller galaxy (except for the "small core" as shown by Ann), and the apparent timeline of only a few million years before we have a "combined larger galaxy", implying the merger would be done by then. What am I missing?

But I did find the stated short timeline pretty unusual if true.

I think it might more than just a few million years. Significant movements on galactic scales are more on the order of 100 million years.

to my eye the canopy part of the umbrella looks like another visible part of mostly invisible shell No 1

VictorBorun wrote: ↑Tue Feb 08, 2022 12:45 am The Umbrella Galaxy.png
to my eye the canopy part of the umbrella looks like another visible part of mostly invisible shell No 1

Yes, it's smooth shape is certainly reminiscent of part of a shell, but I suspect you're implying things that aren't really there. I don't think there is any good evidence to suggest that there are any true shells involved here. As for "shell #2", I don't see anything there at all, at least not in the spherical shape you've drawn. But there is certainly an ovoid cloud or halo of stars around the galaxy.