VictorBorun wrote: ↑
Mon Jan 11, 2021 10:22 pm
What I find surprising about that secretive dusty outskirts beside the fact that it's huge and dwarfing the light-emitting part of the galaxy.
It's clearly non-planar. So the normal matter (can not call it light matter any more) part is overall not a disk but an R=200 kly thorus with an R=20 kly disk brane across the hole. The brane gets thinner at R=4 kly where its prone to form a stable bar ripple, and at R=1 kly there is a core super globular stellar cluster, and at R=1 ly there may be a tiny thorus and disk of accretion by the central black hole.
But how the dusty outskirts survive at such distance from the dark matter globe halo — which is of constant density at R<4 kly and rarefy to nothing at R=40 kly? The dusty skirt is so lose it should have been stripped at encounters with other galaxies.
Maybe they do things different at faraway galaxy clusters. In some each galaxy has a compact dark halo, in others each galaxy has a dusty outskirt.
Victor, much of that is math-speak that you will have to ask someone else about. But I do want to show you another pair of overlapping galaxies.
NGC 3314 is a pair of overlapping but non-interacting galaxies, which is to say that they are so far separated that they don't affect one another gravitationally.
As you can see, the dust lanes of the foreground galaxy, NGC 3314B, look very dark when seen in silhouette against the bright disk of galaxy NGC 3314A. But when seen against the blackness of space, the dust of NGC 3314B almost "disappears". By contrast, the blue star clusters of the arms of NGC 3314B become very obvious against the black background of space, but when seen against the bright background of the disk of NGC 3314A, they almost disappear.
We have good reasons to think that there is more star formation in the extended arms of NGC 3314B than there is closer to the center of that galaxy. It seems likely, too, that there is more dark and concentrated dust closer to the center of NGC 3314B than in the outer parts of the arms.
Still, I think it is remarkable to see how NGC 3314B turns from "brown" when seen in silhouette against the bright disk of NGC 3314A, to "blue" when seen against the blackness of space.