Number 211 (Story #1), January 19, 1995 by Phillip F. Schewe and Ben Stein SUPERLUMINAL JETS FROM AN OBJECT only 10,000 light years away in the Milky Way may help astronomers to better understand the much bigger jets shooting out of distant galaxies. First spotted by the Gamma Ray Observatory in July 1994, the nearby object GRO J1655-40 is probably a double-star system. Matter from the lighter of the two stars is drawn away by gravity onto an accretion disk closely surrounding the heavier (and collapsed) companion, which is thought to be a neutron star or a (few-solar-mass) black hole. One artifact of this process is the flaring up of x rays and gamma rays from the much-heated disk. Indeed GRO J1655-40 is at times the most powerful source of x rays and gamma rays in the galaxy. Another artifact is the production of energetic radio-emitting jets of material which project away from the core object perpendicular to the plane of the disk. These jets appear to be traveling at greater-than-light speeds. This is actually an optical illusion owing to the alignment of the object relative to us, but it does testify to the violent physics taking place in the core. Only one other object in the Milky Way, GRS 1915+105, has been seen to have superluminal jets, but the complex structure of GRO J1655-40 has been mapped with greater resolution, in this case by the Very Long Baseline Array of radio telescopes. One of the astronomers who spoke at last week's astronomy meeting in Tucson, Robert Hjellming of the National Radio Astronomy Observatory, called GRO J1655-40 an astronomical "Rosetta Stone" because studies of the movement of individual blobs within the jets (sometimes on a daily basis) may provide insights about the energy mechanisms at work in the colossal extra-galactic jets produced by presumed supermassive black holes.