Starship Asterisk*

Hi you guys!
I am new here and wanted to ask what these marked features are in yesterdays APOD:

I know, there are hints that there is only one arm but what is this faint thing that looks like a second arm of NGC 4725?
And what are the two light clouds on the left?

Yours,
Qexilber

rstevenson wrote:

Tara_Li wrote:

rstevenson wrote:Eddies can appear in fluid dynamics but not, I think, when the dynamism of a system is driven by gravity. ...

Except that aren't planets supposed to collapse from eddies in the dust clouds around the stars? Sure, there's some magnetic effects in play, but the primary force in the protoplanetary disk is gravity. "Fluid" is kind of a fluid term, really...

Yes, but that's because the gas and dust in a newly forming stellar system can form local aglomerations which gravitationally coalesce into planets. But to get an eddy on a galactic scale you'd need to figure out some way to get entire stellar systems - a great many of them in a group, if they're to appear to us as an eddy - to loop around as they orbit the galactic center of gravity. In other words, they'd need a local center of gravity around which to orbit, just like planets orbit around their star. Conceivably a black hole could collect a few stellar systems around itself, and drag them around the galaxy as it orbits. But I don't think that is gravitationally stable in the long run. It would make for an interesting modelling exercise though.

Why wouldn't a large starbirth nebula, such as the Orion Complex (but perhaps a bit larger) work for that purpose? At what density regime does the Interstellar Medium quit being gravity dominated, and become a fluid? We see turbulance and bowshock in very low density nebulae, after all.

Qexilber wrote:Hi you guys!
I am new here and wanted to ask what these marked features are in yesterdays APOD:

I know, there are hints that there is only one arm but what is this faint thing that looks like a second arm of NGC 4725?
And what are the two light clouds on the left?

Yours,
Qexilber

You may well be right that there are hints of a second arm in NGC 4725. For a spiral to have one well-developed arm and no obvious sign of another is so unusual that it is quite probable that NGC 4725 really does have an "embryonic" second arm.
As for the light clouds on the right, I'd say they are probably dwarf spheroidal satellite galaxies. In the image on the left you can see one of the dwarf spheroidal galaxies that are satellites of the Milky Way. These small galaxies lack star formation, so they contain no young blue stars. Therefore their color is grayish or neutral. They contain very few stars compared with a large galaxy, and their "surface brightness" is low. This kind of galaxies look like faint non-blue smudges.

Ann

Qexilber wrote:
Hi you guys!

I am new here and wanted to ask what these marked features are in yesterdays APOD:

I know, there are hints that there is only one arm but what is this faint thing that looks like a second arm of NGC 4725?

Hi Qexilber! (Quicksilver?)

It is indeed a second arm: http://asterisk.apod.com/viewtopic.php? ... 62#p200213

Qexilber wrote:
And what are the two light clouds on the left?

Distant galaxies (or possibly companion dwarf galaxies of NGC 4712).

Tara_Li wrote:Why wouldn't a large starbirth nebula, such as the Orion Complex (but perhaps a bit larger) work for that purpose? At what density regime does the Interstellar Medium quit being gravity dominated, and become a fluid? We see turbulance and bowshock in very low density nebulae, after all.

One indication that a star forming nebula has insufficient mass to act as a local center of gravity is that after the star formation period ends, the bright new stars are often seen to have proper motions quite different from each other (within the overall motion of the now-dissipated cloud of gas and dust) and they subsequently wander away. The Sun was born in such a region almost 5 billion years ago, but scientists have so far been unable to identify with certainty any of its birth companions.

Of course, clusters can form and remain gravitationally bound, but judging from the location of the clusters that we can see, this doesn't happen within the more crowded regions of a galaxy and therefore can't produce the eddy that sparked this conversation.

Rob

If I crank up the brightness of this APOD, two features stand out to me. (1) the arm of the spiral galaxy seems to end rather abruptly at the 2 o’clock position, instead of “fading out” like it does towards the outside, and (2) there seems to be a “cavity” of lesser star density towards the 8 o’clock position. [Unless I'm making processing artifacts more visible.]

Looks like you found a cosmic snail to me, Case.

geckzilla wrote:Looks like you found a cosmic snail to me, Case.

Any similarity to this?

NGC 772

Nautilus shell

Both from
http://www.stardoctor.org/772.html

Margarita

Thanks to Case and Margarita for your fascinating snails!

Ann

And here all along i was thinking that you guys were FAST Looks like the gecko will have to make up a new smilie, perhaps a 'whizzing' snail

Beyond wrote:And here all along i was thinking that you guys were FAST Looks like the gecko will have to make up a new smilie, perhaps a 'whizzing' snail

Amazing!! A Wheely fast whizzing snail from the Wheely Whizzer that has no wheels to whizz with. ((that's almost a tongue twister))
Either the wheels are too small to see, or it puts out slime as fast as a rotating one-armed galaxy.

Beyond wrote:Amazing!! A Wheely fast whizzing snail from the Wheely Whizzer that has no wheels to whizz with. ((that's almost a tongue twister))

Do NOT try to say that if you've been visiting the Gas Cloud G34.3
http://asterisk.apod.com/viewtopic.php? ... 50#p200324

Margarita

I just noticed something odd about the APOD page for this (https://apod.nasa.gov/apod/ap130530.html). If you click on the Discuss link there, it takes you to http://bb.nightskylive.net/asterisk/dis ... ate=130530, which ends up being a broken link and falls back to a page that proclaims "The domain nightskylive.net may be for sale. Click here for more details". What the heck? I was able to get to the correct page (http://asterisk.apod.com/viewtopic.php?t=31462) by trying the link http://asterisk.apod.com/discuss_apod.php?date=130530 which redirected to the more familiar format - at least to me - of http://asterisk.apod.com/viewtopic.php?t=31462. So, was this the result of some maintenance script gone wrong?

johnnydeep wrote: ↑Sun Jun 07, 2020 4:08 pm I just noticed something odd about the APOD page for this (https://apod.nasa.gov/apod/ap130530.html). If you click on the Discuss link there, it takes you to http://bb.nightskylive.net/asterisk/dis ... ate=130530, which ends up being a broken link and falls back to a page that proclaims "The domain nightskylive.net may be for sale. Click here for more details". What the heck? I was able to get to the correct page (http://asterisk.apod.com/viewtopic.php?t=31462) by trying the link http://asterisk.apod.com/discuss_apod.php?date=130530 which redirected to the more familiar format - at least to me - of http://asterisk.apod.com/viewtopic.php?t=31462. So, was this the result of some maintenance script gone wrong?

Back when men were men and giants walked the Earth, "nightskylive.net" was the host of the APOD discussion forums. So old links may still point the wrong place. I ran into this recently rebuilding my website. I had old links to APOD discussions I needed to fix. Somebody needs to do some kind of global search and replace in order to update the entire APOD site, however.

Chris Peterson wrote: ↑Sun Jun 07, 2020 4:18 pm

johnnydeep wrote: ↑Sun Jun 07, 2020 4:08 pm I just noticed something odd about the APOD page for this (https://apod.nasa.gov/apod/ap130530.html). If you click on the Discuss link there, it takes you to http://bb.nightskylive.net/asterisk/dis ... ate=130530, which ends up being a broken link and falls back to a page that proclaims "The domain nightskylive.net may be for sale. Click here for more details". What the heck? I was able to get to the correct page (http://asterisk.apod.com/viewtopic.php?t=31462) by trying the link http://asterisk.apod.com/discuss_apod.php?date=130530 which redirected to the more familiar format - at least to me - of http://asterisk.apod.com/viewtopic.php?t=31462. So, was this the result of some maintenance script gone wrong?

Back when men were men and giants walked the Earth, "nightskylive.net" was the host of the APOD discussion forums. So old links may still point the wrong place. I ran into this recently rebuilding my website. I had old links to APOD discussions I needed to fix. Somebody needs to do some kind of global search and replace in order to update the entire APOD site, however.

And who is that "somebody" these days? Is there an official web master?