APOD: Rubin's Galaxy (2023 Apr 05)

[Chris Peterson]

even far from the lamp of the core globe, where the dust lanes are backlit from short-living blue stellar population, there may still be hills upon a plain, looking brighter on the side facing the core — if the central black hole(s) sent shock waves to start the star birth where hitting the surface of a hill. May there not?

The core isn't bright enough to illuminate outer structures visibly. How brightly is dust in our own solar system illuminated by the Milky Way compared with by the Sun?

1) from Sun's place under the surface of the disk it's hard to gauge the Milky Way outlook
2) Milky Way may be one of low-contrast pattern disk galaxies with no shock waves from the center during last 100 million years
3) I was trying to say that a relief of bright hills' sides facing the core may result from shock waves hitting the surface of the hills looming above the surface of the disk, if the hit started the starbirth there. Here I thought of such dense interstellar media in the disk, that (1) the relief from the other surface of the disk is not seen through the dust inside the disk and (2) the shock wave that starts the starbirth gets absorbed in a thin layer of the hill's side facing the core

Again, the brightness of the local stars near the dust is orders of magnitude more than that of the background illumination of the core.

[VictorBorun]

The core isn't bright enough to illuminate outer structures visibly. How brightly is dust in our own solar system illuminated by the Milky Way compared with by the Sun?

1) from Sun's place under the surface of the disk it's hard to gauge the Milky Way outlook
2) Milky Way may be one of low-contrast pattern disk galaxies with no shock waves from the center during last 100 million years
3) I was trying to say that a relief of bright hills' sides facing the core may result from shock waves hitting the surface of the hills looming above the surface of the disk, if the hit started the starbirth there. Here I thought of such dense interstellar media in the disk, that (1) the relief from the other surface of the disk is not seen through the dust inside the disk and (2) the shock wave that starts the starbirth gets absorbed in a thin layer of the hill's side facing the core

Again, the brightness of the local stars near the dust is orders of magnitude more than that of the background illumination of the core.

If a local (and far from the core) light spot is stellar and mostly 30 million years old blue giants, and if it's dense because it's on the hill's side facing a recent (30 million years ago) shock wave from the core, then the apparent relief is real after all… that's what I was trying to suggest.

[Chris Peterson]

1) from Sun's place under the surface of the disk it's hard to gauge the Milky Way outlook
2) Milky Way may be one of low-contrast pattern disk galaxies with no shock waves from the center during last 100 million years
3) I was trying to say that a relief of bright hills' sides facing the core may result from shock waves hitting the surface of the hills looming above the surface of the disk, if the hit started the starbirth there. Here I thought of such dense interstellar media in the disk, that (1) the relief from the other surface of the disk is not seen through the dust inside the disk and (2) the shock wave that starts the starbirth gets absorbed in a thin layer of the hill's side facing the core

Again, the brightness of the local stars near the dust is orders of magnitude more than that of the background illumination of the core.

If a local (and far from the core) light spot is stellar and mostly 30 million years old blue giants, and if it's dense because it's on the hill's side facing a recent (30 million years ago) shock wave from the core, then the apparent relief is real after all… that's what I was trying to suggest.

Okay. I'm not familiar with any galaxies that produce shock waves from the core, however.

[Christian G.]

Rubin's Galaxy
...Some 800,000 light-years across compared to the Milky Way's diameter of 100,000 light-years or so, it has around 1 trillion stars...

Hmmm. The press release for this image says:
Galaxy UGC 2885 may be the largest one in the local universe. It is 2.5 times wider than our Milky Way and contains 10 times as many stars.
https://esahubble.org/videos/heic2002b/

More informations:
https://www.youtube.com/watch?v=QWfzEk5m6TY
Start at 11.20

Well...

Wikipedia disagrees on the size of UGC 2885 being 800kly. It also claims that the largest known spiral galaxy is 'only' 650kly.

I think that things got confused across a chain of press releases. With an apparent size of 3.9 arcminutes and a distance of 232 million ly, the diameter works out to 286,000 ly, and I found a couple of direct references to the original report that suggest the size is around 250,000 ly, and also references to it being about 2.5 times the size of the Milky Way. I suspect the "eight times larger" got introduced when somebody confused the mass with the diameter.

Thank you for that video link, a fascinating hour-long presentation on that galaxy - without a single mention of its size! Only the mass. I asked the person who made the presentation, his answer was a 25 kpc half-light radius and close to 200 kpc from outermost arm to outermost arm.