Microquasars are smaller cousins of quasars. They are named after quasars, as they have some common characteristics: strong and variable radio emission often seen as radio jets, and an accretion disk surrounding a black hole. In quasars, the black hole is supermassive (millions of solar masses) as in microquasars, the black hole mass is a few solar masses. In microquasars, the accreted mass comes from a normal star and the accretion disk is very luminous in optical regions and X-rays. Microquasars are sometimes called 'radio-jet X-ray binaries' to distinguish them from other X-ray binaries. A part of the radio emission comes from relativistic jets, often showing apparent superluminal motion.
Microquasars are very important for the study of relativistic jets. The jets are formed close to the black hole, and timescales near the black hole are proportional to the mass of the black hole. Therefore, ordinary quasars take centuries to go through variations a microquasar experiences in one day.
Three-dimensional simulations indicate that spiral shock waves can form in accretion disks, but they also suggest that the disks develop instabilities that tend to smear the shocks (more discussion and images and animations of spiral shocks and of a binary system undergoing mass transfer while rotating around a common center of mass).
XTE J1550-564 belong to an exceptional class of x-ray novae that eject plasma through bi-polar jets at relativistic velocities called microquasars.
Because the spin of XTE J1550-564's progenitor star was concentrated into an extremely compact fl hole during the collapse of the star's core (and rebound into a supernova), the hole is spinning very rapidly.
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