View Full Version here: : ITN: ESO's VLT Great Barred Spiral Shots
23-09-2010, 06:39 AM
In the News: Another zoom-in sequence, this time of NGC 1365 (The Great Barred Spiral Galaxy) taken by the HAWK-I infrared camera on ESO's Very Large TElescope at Paranal Observatory in Chile:
An elegant galaxy in an unusual light (w/ Video) (http://www.physorg.com/news204366868.html)
interestingly the article (journos) say:
Some reading up to do on these latter statements.
… If I can find the paper ...
23-09-2010, 10:46 AM
Just go to arXiv.org and type in barred spiral galaxy formation or dynamics of bars in spiral galaxies. You can do the same in Google Scholar. Or...you can buy this book...Galactic Dynamics (http://www.fishpond.com.au/Books/Science/Astronomy_Space/9780691130279/?cf=3&rid=1298732446&i=5&keywords=astrophysics):)
23-09-2010, 11:01 AM
(This one is almost further to our previous discussions in threads on Rotation Curves)...
Found a really good paper on arXiv this morning. Reasonably recent also (April 2010):
Global disk model for galaxies NGC 1365, NGC 6946, NGC 7793, UGC 6446
Joanna Jałocha1, Łukasz Bratek1, Marek Kutschera and Piotr Skindzier.
An interesting paper. Well balanced, too. They go at it from an 'anything's possible' perspective and put all the known ideas to the test.
Also very interesting to see them considering the possibility that Magnetic fields might be counteracting gravitational forces in the outer arms.
23-09-2010, 11:24 AM
Better hide that stuff about magnetic fields...you know who will have a field day with this if he comes back and sees this:):P
The big problem with that is the very weakness of the magnetic fields. These fields have to drive rotational velocities that can be up to 500kms or more in some of the most massive of the galaxies and 160-220kms for most galaxies in general. You would need a more intense field than what is observed. You not only have to account for the dipole moment of the atoms within the gas/dust clouds being influenced by those fields, you also have to drive the rotation of the stars as well. Considering the magnetic fields of stars are far more intense than the fields in the ISM, I would seriously doubt that these fields would make any headway with influencing the rotation of the stars about the galaxies.
23-09-2010, 12:02 PM
More interesting stuff ..
Aside from the Electromagnetic paragraph (only included to show they have a way of modelling it), Carl, I think you've pointed out before, the importance of getting the model right before making any conclusions about Galaxy Rotation Curves. I think Steven may have, also. It certainly is complex and dependent on the shapes of the Galaxies, matter densities etc.
Lots more work to do in this area, it seems.
23-09-2010, 12:32 PM
They go on to say, in the conclusions, that:
So, in other words;
- some Galaxies don't need any Cold Dark Matter (CDM) to explain their RCs;
- different amounts of CDM needed to explain some Galaxies' RCs;
- different models are needed to explain other Galaxies' RCs.
Not as straightforward as the commonly heard saying: 'flat rotation curves in galaxies means Dark Matter is required to explain them'.
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