**Grant EP/D030544**

Visiting Researcher: Prof. N.O. Santos (2005-6)

Principal Investigator: Prof. M.A.H. MacCallum

## Summary of Final Report

Many astronomical objects emit large-scale jets of particles which
radiate radio waves, visible light, X-rays and so on. The way in which
these jets are formed, so that particles are "collimated", i.e. move
in the same direction, are not fully understood. Approaches so far
rely on numerical simulations, or use Newton's theory of
gravity. Einstein's theory of gravity, general relativity, should be
used but is harder to apply. We succeeded in developing a simple model
for collimation in general relativity using only the geometric
properties of rotating black holes.

The objects themselves form by collapse of large gas clouds under
gravity. This too should be studied in general relativity, but the
effects of radiation and dissipation (essentially friction) have to be
included. We aimed to study the temperature effects in one such model,
and how the resulting body would shine. This work is ongoing.

Finally we wanted to look at other types of collapse which might give
the first exactly described case for the formation of gravitational
waves. By considering possible ways to do this, we developed a
approach which we believe will achieve it in the near future.

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On 10 Nov 2007, 20:05.