JET FORMATION IN MICROQUASARS AND ACTIVE GALACTIC NUCLEI: MAGNETIC FIELD LIMITS

We introduce the use of a well-known parameter, the Alfven Radius, RA, as a new tool to discern whether an X-ray binary system may undergo a microquasarphase, i.e. ejecting relativistic particles orthogonal to the accretion disk. We study what we call the basic condition, RA/R-* = 1 in its dependency on the magnetic field strength and the mass accretion rate. With this basic condition we establish under which combination of parameters any class of accreting neutron stars could become a microquasar instead of con. ning disk-material down to the magnetic poles and creating the two emitting caps typical for an X-ray pulsar. In the case of black-hole accreting binaries we equate the magnetic field pressure to the plasma pressure in the last stable orbit (i.e. R-A/R-LSO = 1) and we get upper limits for the magnetic field strength as a function of the mass accretion rate and the black hole mass.