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SUMMARY:The interplay between cosmological expansion and massive objects -
  Roshina Nandra (Cavendish Astrophysics)
DTSTART:20110524T153000Z
DTEND:20110524T160000Z
UID:TALK30846@talks.cam.ac.uk
CONTACT:Sally Hales
DESCRIPTION:It has been observed that there are definite cut-offs at which
  the radial velocities of particles near galaxies/clusters are exactly zer
 o.  This boundary can be interpreted as the edge of the galaxy/cluster\, w
 here the gravitational attraction of the central object is exactly balance
 d by the cosmological pull due to the universe's expansion.  One may begin
  to explain this phenomenon using a non-zero cosmological constant\, but o
 f course the current universe is not purely de-Sitter.  In this talk I wil
 l present a new theoretical framework for describing a mass particle in a 
 realistically expanding background.  I will show how this leads to a fully
  general relativistic invariant expression for the radial force required t
 o hold a test particle at rest relative to the central mass\, and use it t
 o successfully predict the edges of large-scale objects and also the locat
 ions of maximum stable orbits.  Finally I will present some extensions of 
 this work\, which include the implications for a universe whose expansion 
 is driven by phantom energy\, which leads to a "Big Rip" at a finite time 
 in the future\, and the solutions for spatially curved cosmologies.
LOCATION:Martin Ryle Seminar Room\, Kavli Building
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