mdstuart Posted September 19, 2015 Share Posted September 19, 2015 Just looking through the data of the galaxies I have observed and comparing constellation data for those where I have a larger sample.I noted that there are far more spiral galaxies in the Plough (70%) than in Virgo (43%) as a % of all those I have seen. There are a lot more elliptical galaxies in Virgo.So why is that? I presume its because the Virgo galaxies are in a tighter group and have undergone a load of mergers and hence the different mix.Anyway just quite interesting to note.Mark Link to comment Share on other sites More sharing options...
Paul73 Posted September 19, 2015 Share Posted September 19, 2015 Sounds plausible. Interesting observation.Might be worth a few minutes with a database to validate.Paul Link to comment Share on other sites More sharing options...
Tiki Posted September 20, 2015 Share Posted September 20, 2015 So why is that? I presume its because the Virgo galaxies are in a tighter group and have undergone a load of mergers and hence the different mix. Anyway just quite interesting to note. Mark I believe your presumption is also the consensus of opinion amongst scientists. It is thought that elliptical galaxies are very old structures and have undergone loads of collisions and mergers, hence their relatively high prevalence in crowded regions of the cosmos. Well spotted. BTW, your galaxy count is very impressive. Link to comment Share on other sites More sharing options...
acey Posted September 20, 2015 Share Posted September 20, 2015 Spirals outnumber ellipticals in the universe as a whole. Various figures are given, for example 77% spirals versus 20% ellipticals (and 3% irregular)http://skyserver.sdss.org/dr1/en/proj/advanced/galaxies/separator.aspIf spirals interact with each other gravitationally then tidal forces disrupt their spiral form, strip them of star-forming dust, and ultimately leave them as ellipticals.So ellipticals are more common in dense galaxy clusters, while isolated galaxies, or ones in sparser clusters, are more likely to be spirals.For the Virgo Cluster, among its 205 brightest galaxies, 68% are spirals, but the 4 brightest are giant ellipticals.http://ned.ipac.caltech.edu/level5/March02/Abell/Abell3_2.htmlIf fainter galaxies are included, then out of about 2000 galaxies in the Virgo Cluster, 58% are spirals.http://www.britannica.com/place/Virgo-clusterSo the Virgo Cluster has less than the general proportion of spirals, because of interactions that have turned spirals into ellipticals.Edit:I just had a look at the NGC/IC (on Excel spreadsheet) and did a quick (slightly rough) count. I got that 15% of NGC/IC objects are elliptical galaxies, 61% are spiral galaxies; i.e. spirals outnumber ellipticals in the NGC/IC by roughly 4 to 1. May not be completely accurate - if I'd spent more than two minutes I might have got a slightly different figure. Link to comment Share on other sites More sharing options...
Macavity Posted September 20, 2015 Share Posted September 20, 2015 As an "I've never really known" question: Do galaxies rotate in senseof trailing their arms as if in some (clearly non-existant!) breeze? I'm sure I saw somewhere that some galaxies have a contra-rotatingstructure, but let's keep this to simple spiral gx's for the moment? Link to comment Share on other sites More sharing options...
mdstuart Posted September 20, 2015 Author Share Posted September 20, 2015 Thanks Acey..Macavity I do not think the arms rotate as such but a rotating gravity wave makes the shape we see...I think! Link to comment Share on other sites More sharing options...
Macavity Posted September 21, 2015 Share Posted September 21, 2015 Perhaps a bad choice of words. (Or my inadequate "research"!)It seems that Wikipedia amply covers the "rotation curves" etc.,but rarely mentions initial global rotation direction of galaxies. Such is revealed (supposedly) in one of many Youtube videosof Galaxy mergers. It seems that spiral galaxies do indeed rotate much like a "Catherine Wheel" - At least initially! Link to comment Share on other sites More sharing options...
Paul73 Posted September 21, 2015 Share Posted September 21, 2015 Nice video Chris. Does YouTube state a source?Paul Link to comment Share on other sites More sharing options...
Macavity Posted September 21, 2015 Share Posted September 21, 2015 As a notable change (for things likeYoutube?) This movie won a semifinalist honor (top ten in the category) in the 2008 NSF Science & Engineering Visualization Challenge, and was also featured in the National Geographic Special "Inside the Milky Way" in 2010. A high-quality version can be downloaded from http://code.google.com/p/sunrise/wiki...etc. etc.The link is broken, even on the Youtube page. But: https://bitbucket.org/lutorm/sunrise Link to comment Share on other sites More sharing options...
Paul73 Posted September 21, 2015 Share Posted September 21, 2015 Cool. We'll take that as reputable.Thanks for looking it up.Paul Link to comment Share on other sites More sharing options...
Tiki Posted September 21, 2015 Share Posted September 21, 2015 As an "I've never really known" question: Do galaxies rotate in sense of trailing their arms as if in some (clearly non-existant!) breeze? Apparently M33 does. (This can be inferred from the graph on the top right-hand side of this page: https://en.wikipedia.org/wiki/Galaxy_rotation_curve) Link to comment Share on other sites More sharing options...
Macavity Posted September 21, 2015 Share Posted September 21, 2015 So, most seem to follow the general scheme...But: https://en.wikipedia.org/wiki/NGC_4622 (!)Evidently such things are still of interest... The inverse of this lone voice? [https://www.youtube.com/watch?v=jVygqjyS4CA](M.Python "You're all different") Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.