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.rstevenson wrote: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.Tara_Li wrote: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...rstevenson wrote:Eddies can appear in fluid dynamics but not, I think, when the dynamism of a system is driven by gravity. ...
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.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
Hi Qexilber! (Quicksilver?)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?
Distant galaxies (or possibly companion dwarf galaxies of NGC 4712).Qexilber wrote:
And what are the two light clouds on the left?
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.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.
Any similarity to this?geckzilla wrote:Looks like you found a cosmic snail to me, Case.
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
Do NOT try to say that if you've been visiting the Gas Cloud G34.3Beyond wrote:Amazing!! A Wheely fast whizzing snail from the Wheely Whizzer that has no wheels to whizz with. ((that's almost a tongue twister))
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.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?
And who is that "somebody" these days? Is there an official web master?Chris Peterson wrote: ↑Sun Jun 07, 2020 4:18 pmBack 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.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?
