A hole in the leading theory of quasars may now have been filled by results announced in the 10 December Astrophysical Journal. Shining brightly in the far reaches of the universe, quasars are the most energetic objects known. Their extraordinary brilliance, most astronomers believe, is powered by black holes as massive as millions of suns, dragging material into the centers of young galaxies and heating them to incandescence.
Radio-emitting jets of material that squirt at close to the speed of light from the centers of some quasars provide strong support for this scenario. Such relativistic jets, theorists believe, can only originate from the surroundings of a massive black hole. But why only a tenth of all quasars--the "radio-loud" ones--seem to harbor these jets has remained a mystery. Now a team of radio astronomers led by Heino Falcke of the University of Maryland has found strong indirect evidence that most of the remaining quasars, if not all of them, have unseen plasma jets.
The team's observations of a class of quasars with radio luminosities midway between radio-loud and radio-quiet quasars reveal extremely bright, compact points of radio emission. Falcke and his colleagues believe that this bright, focused emission emanates from plasma jets aimed straight along the line of sight, for Einstein's theory of relativity predicts that radiation will be amplified if its source is moving toward the observer at relativistic speeds. Falcke argues that these "radio-intermediate" quasars are the same kind of objects as the radio-quiet quasars, except that "we happen to look right into a jet." If so, other radio-quiet quasars--which make up 90% of the quasar population--would also contain relativistic jets in their nuclei, pointing away from Earth.>
Falcke's suggestion is "a viable picture," says Robert Antonucci, a quasar expert at the University of California, Santa Barbara. "If I had to vote on it, I'd say they are probably right." With that intellectual hole filled, the case for black holes in quasars would become even stronger.