APOD: Rubin's Galaxy (2023 Apr 05)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 5549
Joined: Fri Dec 04, 2009 3:27 am

APOD: Rubin's Galaxy (2023 Apr 05)

Post by APOD Robot » Wed Apr 05, 2023 4:06 am

Image Rubin's Galaxy

Explanation: In this Hubble Space Telescope image the bright, spiky stars lie in the foreground toward the heroic northern constellation Perseus and well within our own Milky Way galaxy. In sharp focus beyond is UGC 2885, a giant spiral galaxy about 232 million light-years distant. 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. That's about 10 times as many stars as the Milky Way. Part of an investigation to understand how galaxies can grow to such enormous sizes, UGC 2885 was also part of An Interesting Voyage and astronomer Vera Rubin's pioneering study of the rotation of spiral galaxies. Her work was the first to convincingly demonstrate the dominating presence of dark matter in our universe.

<< Previous APOD This Day in APOD Next APOD >>

User avatar
AVAO
Commander
Posts: 746
Joined: Tue May 28, 2019 12:24 pm
AKA: multiwavelength traveller
Location: Zurich, Switzerland

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by AVAO » Wed Apr 05, 2023 4:30 am

APOD Robot wrote: Wed Apr 05, 2023 4:06 am Image 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...
Chris Peterson wrote: Sat Jan 25, 2020 2:56 pm
rj rl wrote: Sat Jan 25, 2020 9:59 am 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.

User avatar
Ann
4725 Å
Posts: 13764
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Ann » Wed Apr 05, 2023 5:46 am

Disregarding the exact size of Rubin's Galaxy, it is clearly "unreasonably large" as spiral galaxies go. And the most likely explanation for how it got that way, if you ask a math idiot like me, is that it has merged with one or more other spiral galaxies in such a way that the physical parameters of the merger process supported the spiral structure of the merger product.

Or, in other words: Normally, when two (similarly sized) spiral galaxies collide, we expect their spiral structures to become hopelessly messed up beyond repair, so that the merger product will be a large elliptical galaxy. But in a precious few cases, the processes when two large spiral galaxies merge may enhance and not mess up the spiral structure of the large galaxy that is born out of the merger.

And, hey presto, that way we got a spiral galaxy that is twice as big as the two spiral galaxies that created it!

That's what I think anyway!

Ann
Color Commentator

Prof Greg Parker

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Prof Greg Parker » Wed Apr 05, 2023 7:43 am

I really do not understand why Social Media is trying desperately to re-write history in this way. Every man and his dog is fully aware that Fritz Zwicky was the first to demonstrate the presence of dark matter by the studying the Coma cluster of galaxies (using the virial theorem just as Rubin did).

In 1933, Zwicky was the first to use the virial theorem to postulate the existence of unseen dark matter, describing it as "dunkle Materie".

It matters not a jot whether you think that "Her work was the first to convincingly demonstrate the dominating presence of dark matter in our universe" it was Zwicky that first discovered dark matter. I wish I could say I am astounded by your blatant misrepresentation - but I see wokeness taking over everywhere - so I'm not too surprised.

User avatar
AVAO
Commander
Posts: 746
Joined: Tue May 28, 2019 12:24 pm
AKA: multiwavelength traveller
Location: Zurich, Switzerland

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by AVAO » Wed Apr 05, 2023 12:04 pm

Prof Greg Parker wrote: Wed Apr 05, 2023 7:43 am I really do not understand why Social Media is trying desperately to re-write history in this way. Every man and his dog is fully aware that Fritz Zwicky was the first to demonstrate the presence of dark matter by the studying the Coma cluster of galaxies (using the virial theorem just as Rubin did).

In 1933, Zwicky was the first to use the virial theorem to postulate the existence of unseen dark matter, describing it as "dunkle Materie".

It matters not a jot whether you think that "Her work was the first to convincingly demonstrate the dominating presence of dark matter in our universe" it was Zwicky that first discovered dark matter. I wish I could say I am astounded by your blatant misrepresentation - but I see wokeness taking over everywhere - so I'm not too surprised.
As a Swiss, a friend of astronomy and an ardent supporter of morphology, I share your appreciation of Fritz Zwicky as a person. I think your criticism is in a way justified, given that Fritz Zwicky was certainly the first to discover that certain proper motions of galaxies can only be explained by additional masses. It is also the case that at least 30 other astronomers dealt with the topic between 1933 and the studies by Ford and Rubin in 1971, and there were even entire conferences focusing on this topic in the meantime. Regardless of this, Vera Rubin made a significant contribution to the precision of the verification.

Details: https://ned.ipac.caltech.edu/level5/Sep ... tone3.html
Last edited by AVAO on Wed Apr 05, 2023 8:40 pm, edited 3 times in total.

sc02492
Ensign
Posts: 23
Joined: Tue Apr 20, 2010 9:41 pm
AKA: Steve Cannistra

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by sc02492 » Wed Apr 05, 2023 2:32 pm

Prof Greg Parker wrote: Wed Apr 05, 2023 7:43 am Every man and his dog is fully aware that Fritz Zwicky was the first to demonstrate the presence of dark matter by the studying the Coma cluster of galaxies (using the virial theorem just as Rubin did).
I was also very surprised that there was no mention of Fritz Zwicky in the APOD text. Since a lot of young, budding astronomers read APOD, and in the interest of historical accuracy, it would be a nice gesture if the APOD editors would consider amending the text to recognize Zwicky's original contribution to this area.

Steve

Steve Cannistra
www.starrywonders.com
Last edited by sc02492 on Wed Apr 05, 2023 10:14 pm, edited 1 time in total.

User avatar
Chris Peterson
Abominable Snowman
Posts: 18534
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Chris Peterson » Wed Apr 05, 2023 3:02 pm

sc02492 wrote: Wed Apr 05, 2023 2:32 pm
Prof Greg Parker wrote: Wed Apr 05, 2023 7:43 am Every man and his dog is fully aware that Fritz Zwicky was the first to demonstrate the presence of dark matter by the studying the Coma cluster of galaxies (using the virial theorem just as Rubin did).
I was also very surprised that there was no mention of Fritz Zwicky in the APOD text. Since a lot of young, budding astronomers read APOD, and in the interest of historical accuracy, it would be a nice gesture if the APOD editors would consider amending the text to recognize Zwicky's ground-breaking contribution to this area.
I don't think that belongs in this caption at all. The subject of this APOD is not dark matter, it is a specific galaxy. A galaxy that has a particular significance because of its role in the use of galaxy rotation curves as evidence for dark matter. And that work was Rubin's, not Zwicky's. His name would be appropriate in discussing and image of, say, the Coma Cluster, which was the basis of the very different observational evidence (galaxy proper motions) that led to his earlier ideas about dark matter.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com

Prof. Greg Parker

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Prof. Greg Parker » Wed Apr 05, 2023 4:51 pm

Thank you Chris for the expected woke response - you did not disappoint me.
The disagreement is nothing to do with the subject of the APOD (the galaxy) - as you well understand.
The disagreement is with the final sentence of the APOD caption - " Her work was the first to convincingly demonstrate the dominating presence of dark matter in our universe". It wasn't - the entire astronmical community knows it wasn't. But APOD it seems believes it was.

User avatar
Chris Peterson
Abominable Snowman
Posts: 18534
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Chris Peterson » Wed Apr 05, 2023 4:59 pm

Prof. Greg Parker wrote: Wed Apr 05, 2023 4:51 pm Thank you Chris for the expected woke response - you did not disappoint me.
The disagreement is nothing to do with the subject of the APOD (the galaxy) - as you well understand.
The disagreement is with the final sentence of the APOD caption - " Her work was the first to convincingly demonstrate the dominating presence of dark matter in our universe". It wasn't - the entire astronmical community knows it wasn't. But APOD it seems believes it was.
Well, I am "woke", as any ethical person is. But this has nothing to do with that. And the final sentence is accurate. It wasn't until the work with galaxy rotation curves that any accurate metrics for dark matter began to become clear. Those were, indeed, the discoveries that galvanized our modern ideas about dark matter. That observation in no way detracts from the work of Zwicky and earlier astronomers who made the initial discoveries that raised the possibility of dark matter.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com

User avatar
Ann
4725 Å
Posts: 13764
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Ann » Wed Apr 05, 2023 5:55 pm

Let's get back to discussing the galaxy in question, shall we? :wink:

I wrote in my previous post:
Disregarding the exact size of Rubin's Galaxy, it is clearly "unreasonably large" as spiral galaxies go. And the most likely explanation for how it got that way, if you ask a math idiot like me, is that it has merged with one or more other spiral galaxies in such a way that the physical parameters of the merger process supported the spiral structure of the merger product.
Hmmm. I said that Rubin's Galaxy is most likely a merger product, but maybe not. No according to Wikipeida:
Wikipedia wrote:
UGC 2885 is classified as a field galaxy—a class of galaxies found in remote, under-dense and “vacant” sections of space, far from other major galaxies. NASA has reported that the theorized main source for disk growth for UGC 2885 came from the accretion of intergalactic hydrogen gas, rather than through the repeated process of galactic collision, as most galaxies are thought to grow.

Right. Rubin's Galaxy is a field galaxy, sailing the cosmic seas in more or less splendid isolation. As such, it is free to gobble up any free hydrogen that comes its way. And there are no predators nearby to disturb its meal.

No wonder it has grown wider still and wider.

Ann
Color Commentator

User avatar
johnnydeep
Commodore
Posts: 3155
Joined: Sun Feb 20, 2011 8:57 pm

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by johnnydeep » Wed Apr 05, 2023 7:31 pm

Chris Peterson wrote: Wed Apr 05, 2023 4:59 pm
Prof. Greg Parker wrote: Wed Apr 05, 2023 4:51 pm Thank you Chris for the expected woke response - you did not disappoint me.
The disagreement is nothing to do with the subject of the APOD (the galaxy) - as you well understand.
The disagreement is with the final sentence of the APOD caption - " Her work was the first to convincingly demonstrate the dominating presence of dark matter in our universe". It wasn't - the entire astronmical community knows it wasn't. But APOD it seems believes it was.
Well, I am "woke", as any ethical person is. But this has nothing to do with that. And the final sentence is accurate. It wasn't until the work with galaxy rotation curves that any accurate metrics for dark matter began to become clear. Those were, indeed, the discoveries that galvanized our modern ideas about dark matter. That observation in no way detracts from the work of Zwicky and earlier astronomers who made the initial discoveries that raised the possibility of dark matter.
Plus, the final link in the text has this to say:
https://www.space.com/vera-rubin.html wrote:Swiss astronomer, Fritz Zwicky, first proposed the existence of dark matter in 1933 after observing the motion of galaxies in the Coma Cluster. The cluster of galaxies he observed should have flown apart if there was no additional mass holding them together. Lacking further evidence, his idea was quickly dismissed by the scientific community.

Thanks in large part to Rubin's work, scientists now believe that only about 20% of matter in the universe is visible. The other 80% is dark matter.
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}

mountainjim62

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by mountainjim62 » Wed Apr 05, 2023 8:22 pm

All ethical people are woke? Hmmmm. So I guess it is OK to say that all people who are very intelligent lack common sense? Seems very appropriate for this conversation.

ErasmusRoterodamus

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by ErasmusRoterodamus » Wed Apr 05, 2023 9:28 pm

Aside from all controversy, WOW! what a beautiful galaxy! Looks a lot like home! Thank You, Hubbell, and APOD!!

sc02492
Ensign
Posts: 23
Joined: Tue Apr 20, 2010 9:41 pm
AKA: Steve Cannistra

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by sc02492 » Wed Apr 05, 2023 9:59 pm

Chris Peterson wrote: Wed Apr 05, 2023 3:02 pm The subject of this APOD is not dark matter, it is a specific galaxy. A galaxy that has a particular significance because of its role in the use of galaxy rotation curves as evidence for dark matter. And that work was Rubin's, not Zwicky's.
Chris, I understand your point. However, the main subject is not only the specific galaxy, but also the critical role that Vera Rubin played in validating the concept of dark matter. This did not happen in isolation. Providing some historical context by mentioning Zwicky's initial observation, if only briefly, would have provided readers unfamiliar with the topic greater insight into the process of scientific discovery. Science is a step-wise process that benefits from the contributions of many people over time, who build upon each other's observations.

The link in the last sentence of the caption provides a lot of good information about this discovery, so hopefully people will check it out.

Steve

Steve Cannistra
www.starrywonders.com

User avatar
Chris Peterson
Abominable Snowman
Posts: 18534
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Chris Peterson » Wed Apr 05, 2023 10:29 pm

sc02492 wrote: Wed Apr 05, 2023 9:59 pm
Chris Peterson wrote: Wed Apr 05, 2023 3:02 pm The subject of this APOD is not dark matter, it is a specific galaxy. A galaxy that has a particular significance because of its role in the use of galaxy rotation curves as evidence for dark matter. And that work was Rubin's, not Zwicky's.
Chris, I understand your point. However, the main subject is not only the specific galaxy, but also the critical role that Vera Rubin played in validating the concept of dark matter. This did not happen in isolation. Providing some historical context by mentioning Zwicky's initial observation, if only briefly, would have provided readers unfamiliar with the topic greater insight into the process of scientific discovery. Science is a step-wise process that benefits from the contributions of many people over time, who build upon each other's observations.

The link in the last sentence of the caption provides a lot of good information about this discovery, so hopefully people will check it out.

Steve

Steve Cannistra
www.starrywonders.com
I think it would have detracted from the caption to reference Zwicky here. Nothing happens in isolation, but captions aren't designed to give an entire history. Rubin's work is fundamentally what defined the modern science around dark matter. And this galaxy was important to her studies. So the caption as is works just fine.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com

User avatar
Fred the Cat
Theoretic Apothekitty
Posts: 975
Joined: Mon Feb 22, 2016 4:09 pm
AKA: Ron
Location: Eagle, Idaho

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Fred the Cat » Thu Apr 06, 2023 12:09 am

A bit longer discussion of this galaxy goes into a bit more detail. About 30 minutes in runs a perspective animation off of a credited Geck image.

Odd that bright star was once thought too bright for Hubble :?:
Freddy's Felicity "Only ascertain as a cat box survivor"

User avatar
orin stepanek
Plutopian
Posts: 8200
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by orin stepanek » Thu Apr 06, 2023 12:42 am

RubinsGalaxy_hst1024.jpg
I didn't have much time; but enough time to admire this photo! Very
nice! 8-)
You do not have the required permissions to view the files attached to this post.
Orin

Smile today; tomorrow's another day!

User avatar
Ann
4725 Å
Posts: 13764
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Ann » Thu Apr 06, 2023 4:28 am

Consider what Wikipedia wrote about Fritz Zwicky:
Wikipedia wrote:

Supernovae and neutron stars

Together with colleague Walter Baade, Zwicky pioneered and promoted the use of the first Schmidt telescopes used in a mountain-top observatory in 1935. In 1934 he and Baade coined the term "supernova" and hypothesized that supernovae were the transition of normal stars into neutron stars, as well as the origin of cosmic rays. This was an opinion which contributed to determining the size and age of the universe subsequently.

In support of this hypothesis, Zwicky started looking for supernovae, and found a total of 120 by himself (and one more, SN 1963J, in concert with Paul Wild) over 52 years (SN 1921B through SN 1973K), a record which stood until 2009 when passed by Tom Boles. Zwicky did his laborious work, comparing photographic plates with the human eye, which is far more challenging and difficult than Boles accomplished using modern technology for his record.

Gravitational lenses

In 1937, Zwicky posited that galaxies could act as gravitational lenses by the previously discovered Einstein effect.[19] It was not until 1979 that this effect was confirmed by observation of the so-called "Twin Quasar" Q0957+561.

Dark matter

While examining the Coma galaxy cluster in 1933, Zwicky was the first to use the virial theorem to discover the existence of a gravitational anomaly, which he termed dunkle Materie 'dark matter'.[3] The gravitational anomaly surfaced due to the excessive rotational velocity of luminous matter compared to the calculated gravitational attraction within the cluster. He calculated the gravitational mass of the galaxies within the cluster from the observed rotational velocities and obtained a value at least 400 times greater than expected from their luminosity. The same calculation today shows a smaller factor, based on greater values for the mass of luminous material.

Tired light

When Edwin Hubble discovered a somewhat linear relationship between the distance to a galaxy and its redshift expressed as a velocity,[22] Zwicky immediately pointed out that the correlation between the calculated distances of galaxies and their redshifts had a discrepancy too large to fit in the distance's error margins. He proposed that the reddening effect was not due to motions of the galaxy, but to an unknown phenomenon that caused photons to lose energy as they traveled through space. He considered the most likely candidate process to be a drag effect in which photons transfer momentum to surrounding masses through gravitational interactions; and proposed that an attempt be made to put this effect on a sound theoretical footing with general relativity. He also considered and rejected explanations involving interactions with free electrons, or the expansion of space.[23]

Zwicky was skeptical of the expansion of space in 1929, because the rates measured at that time seemed too large. It was not until 1956 that Walter Baade corrected the distance scale based on Cepheid variable stars, and ushered in the first accurate measures of the expansion rate.[24] Cosmological redshift is now conventionally understood to be a consequence of the expansion of space; a feature of Big Bang cosmology.

(...)

Original thinker

Zwicky was an original thinker, and his contemporaries frequently had no way of knowing which of his ideas would work out and which would not. In a retrospective look at Zwicky's life and work, Stephen Maurer said:

When researchers talk about neutron stars, dark matter, and gravitational lenses, they all start the same way: "Zwicky noticed this problem in the 1930s. Back then, nobody listened..."

Let me add that while Zwicky was wrong about his hypothesis of tired light, he was right that the cosmic expansion rate that Hubble originally proposed was way, way too high.

Zwicky was certainly a genius.

Ann
Color Commentator

User avatar
VictorBorun
Captain
Posts: 1124
Joined: Fri Oct 16, 2020 10:25 pm

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by VictorBorun » Thu Apr 06, 2023 2:40 pm

Ann wrote: Wed Apr 05, 2023 5:46 am Disregarding the exact size of Rubin's Galaxy, it is clearly "unreasonably large" as spiral galaxies go.
Ann
How flat is this disk? My vision tends to interpret the dust lanes as illuminated mostly by the core and shadowed in some places by dusty hills on the plain of the disk.
RubinsGalaxy_hst2000.jpg-.jpg
You do not have the required permissions to view the files attached to this post.

User avatar
Chris Peterson
Abominable Snowman
Posts: 18534
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Chris Peterson » Thu Apr 06, 2023 2:48 pm

VictorBorun wrote: Thu Apr 06, 2023 2:40 pm
Ann wrote: Wed Apr 05, 2023 5:46 am Disregarding the exact size of Rubin's Galaxy, it is clearly "unreasonably large" as spiral galaxies go.
Ann
How flat is this disk? My vision tends to interpret the dust lanes as illuminated mostly by the core and shadowed in some places by dusty hills on the plain of the disk.
That's an illusion. There is no "central" lighting at all. Everything we see is locally lit.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com

ybznek

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by ybznek » Sat Apr 08, 2023 9:36 am

Hey, this one was here two years ago! :-(
https://apod.nasa.gov/apod/ap210918.html

User avatar
VictorBorun
Captain
Posts: 1124
Joined: Fri Oct 16, 2020 10:25 pm

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by VictorBorun » Sat Apr 08, 2023 10:01 am

Chris Peterson wrote: Thu Apr 06, 2023 2:48 pm
VictorBorun wrote: Thu Apr 06, 2023 2:40 pm
Ann wrote: Wed Apr 05, 2023 5:46 am Disregarding the exact size of Rubin's Galaxy, it is clearly "unreasonably large" as spiral galaxies go.
Ann
How flat is this disk? My vision tends to interpret the dust lanes as illuminated mostly by the core and shadowed in some places by dusty hills on the plain of the disk.
That's an illusion. There is no "central" lighting at all. Everything we see is locally lit.
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?

User avatar
Chris Peterson
Abominable Snowman
Posts: 18534
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Chris Peterson » Sat Apr 08, 2023 12:39 pm

VictorBorun wrote: Sat Apr 08, 2023 10:01 am
Chris Peterson wrote: Thu Apr 06, 2023 2:48 pm
VictorBorun wrote: Thu Apr 06, 2023 2:40 pm

How flat is this disk? My vision tends to interpret the dust lanes as illuminated mostly by the core and shadowed in some places by dusty hills on the plain of the disk.
That's an illusion. There is no "central" lighting at all. Everything we see is locally lit.
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?
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com

Christian G.
Science Officer
Posts: 222
Joined: Sat Apr 08, 2023 10:37 pm

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by Christian G. » Sat Apr 08, 2023 10:47 pm

In her paper "UGC 2885, the largest known spiral galaxy", Rubin writes "its diameter is its claim to fame: it is 250 000 parsecs". Press releases sometimes use the exact same figure, 250 000, but replace parsecs with light-years, and of course that's a huge difference. So, either Rubin was way off the mark, or some press release got things mixed up one day.
Last edited by Christian G. on Sun Apr 09, 2023 4:52 pm, edited 1 time in total.

User avatar
VictorBorun
Captain
Posts: 1124
Joined: Fri Oct 16, 2020 10:25 pm

Re: APOD: Rubin's Galaxy (2023 Apr 05)

Post by VictorBorun » Sun Apr 09, 2023 5:53 am

Chris Peterson wrote: Sat Apr 08, 2023 12:39 pm
VictorBorun wrote: Sat Apr 08, 2023 10:01 am
Chris Peterson wrote: Thu Apr 06, 2023 2:48 pm

That's an illusion. There is no "central" lighting at all. Everything we see is locally lit.
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