Seeing double.

Seeing double

Astronomers have found what theythink is the first known pair of quasars, sitting neatly together some 12 billion light-years away in the direction of the constellation Crater. Only one of the two quasars, which are 4.2 arc seconds apart, registers in radio wavelengths, while both can be seen in the visible range. This rules out the possibility that the quasar is imaged through a gravitational lens, which would split the image of one quasar into two and cause both to be recorded identically in radio and visible wavelengths.

The spectra of the quasars, whichcould be circling one another or members of passing galaxies, also showed subtle differences in their physical makeup. Although a quasar has been known to exist in that region, December observations were first to uncover its binary nature. The study, led by the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., will be published in an upcoming issue of ASTROPHYSICAL JOURNAL LETTERS.