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BEGIN:VEVENT
DTSTART;TZID=Atlantic/Canary:20171130T103000
DTEND;TZID=Atlantic/Canary:20171130T113000
UID:iactalks-1096
X-WR-CALNAME: IAC Talks: Open Astronomy Seminars
X-ORIGINAL-URL: /iactalks/Talks/view/1096
CREATED:2017-11-30T10:30:00+00:00
X-WR-CALDESC: IAC Talks upcomming talks
SUMMARY:Transient spiral arms and galaxy rotation curves
DESCRIPTION:Transient spiral arms and galaxy rotation curves\nDr. Francesco
  Sylos-Labini\n\nWe describe how a simple class         of out of equilibr
 ium, rotating and asymmetrical mass         distributions evolve under the
 ir self-gravity to produce a         quasi-planar spiral structure surroun
 ding a virialized core,         qualitatively resembling a spiral galaxy. 
 The spiral structure         is transient, but can survive tens of dynamic
 al times, and         further reproduces qualitatively noted features of s
 piral         galaxies as the predominance of trailing two-armed spirals a
 nd         large pitch angles. As our models are highly idealized, a      
    detailed comparison with observations is not appropriate, but         g
 eneric features of the velocity distributions can be identified         to
  be potential observational signatures of such a mechanism.         Indeed
 , the mechanism leads generically to a characteristic         transition f
 rom predominantly rotational motion, in a region         outside the core,
  to radial ballistic motion in the outermost         parts. Such radial mo
 tions are excluded in our Galaxy up to 15         kpc, but could be detect
 ed at larger scales in the future by         GAIA. We explore the apparent
  motions seen by external observers         of the velocity distributions 
 of our toy galaxies, and find that         it is difficult to distinguish 
 them from those of a rotating         disc with sub-dominant radial motion
 s at levels typically         inferred from observations. These simple mod
 els illustrate the         possibility that the observed apparent motions 
 of spiral         galaxies might be explained by non-trivial non-stationar
 y mass         and velocity distributions without invoking a dark matter h
 alo         or modification of Newtonian gravity. In this scenario the    
      observed phenomenological relation between the centripetal and       
   gravitational acceleration of the visible baryonic mass could         ha
 ve a simple explanation.
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