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Paul Alexander
P.Alexander@mrao.cam.ac.uk

Cavendish Astrophysics

Galaxy Evolution

Micro Quasars


Radio imaging of an outburst in the "micro-quasar" GRS1915 +105 made with the MERLIN array.  To capture this comparatively rare event regular monitoring of the system is performed using an international network of observatories.  This outburst was first noted, and these observations triggered, using the Ryle Telescope.
 

The ejection of matter at relativistic speeds seems to be a universal feature of Active Galactic Nuclei - radio galaxies and quasars. In the last few years a very similar phenomenon has been observed in some X-ray binaries, binary stellar systems with one gravitationally-compact object (black hole or neutron star) and an "normal" star part of whos atmosphere is captured by the compact object.

The material captured in this way forms an accretion disc which emits X-rays, and sometimes material is ejected at relativistic speeds, presumably along the rotation axis of the compact object, forming small-scale analogues of radio galaxies and quasars - hence the name "microquasars".

The compact objects (a few solar masses) are much smaller than those inferred in AGN (109 solar masses), and the sizes much smaller, so the analogy may not be complete. Nevertheless, it is relatively easy to study their evolution (they last a few days, and they are much closer).  Some are apparently single events, others repeat at intervals of months or years.

We use the Ryle Telescope to monitor a small number of these microquasars, and use combinations of radio and X-ray monitoring to trigger mapping observations with long-baseline arrays (e.g. the VLBA).


University of Cambridge    Last modified: 27/1/2002