1 Introduction

Recent studies suggest that when cold nuclear matter is compressed to high nuclear densities, diquarks with spin zero and antisymmetric color wave function Bose-condensate into a superfluid/superconducting state that is several times as dense (e.g., Rapp et al. 1998; Wilczek 1998). Various astrophysical phenomena may be explained by gravitational collapse of neutron stars (NSs) to (di)quark stars (QSs) as a result of a first order phase transition in NSs within $\sim 10^{4}$ years after their birth in supernova explosions, when they cooled and spun down sufficiently (by magnetic braking?). The gravitational energy release drives an explosion which may eject both highly relativistic narrowly collimated jets and a mildly relativistic "spherical'' shell. The jets can produce the observed gamma ray bursts (GRBs) and their afterglows in distant galaxies when they happen to point in our direction. The spherical ejecta produces additional supernova like afterglow. The slow contraction/cooling of the remnant QSs can power soft gamma ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs), without invoking a huge magnetic energy storage. The jets distort the original supernova remnant (SNR), sweep up ambient matter along their trajectories, accelerate it to cosmic ray (CR) energies and disperse it in hot spots which they form when they stop in the galactic halo. Such events in our Galaxy may be the main source of Galactic cosmic rays at all energies (Dar & Plaga 1999).