ISCOs and OSCOs in the presence of positive cosmological constant
  Normally one thinks of the observed cosmological constant as being so small
that it can be utterly neglected on typical astrophysical scales, only
affecting extremely large-scale cosmology at Gigaparsec scales. Indeed, in
those situations where the cosmological constant only has a quantitative
influence on the physics, a separation of scales argument guarantees the effect
is indeed negligible. The exception to this argument arises when the presence
of a cosmological constant qualitatively changes the physics. One example of
this phenomenon is the existence of outermost stable circular orbits (OSCOs) in
the presence of a positive cosmological constant. Remarkably the size of these
OSCOs are of a magnitude to be astrophysically interesting. For instance: for
galactic masses the OSCOs are of order the inter-galactic spacing, for galaxy
cluster masses the OSCOs are of order the size of the cluster.
