'Apparent' gravitational lens questioned.

'Apparent' gravitational lens questioned

Two quasars very close together in the sky, catalogued as 1146+111B,C, may be a double image of a single quasar formed by the largest gravitational lens yet discovered (SN: 5/17/86, p. 310), or they may not be. Observations are now causing some astronomers to question the suggestion of a gravitational lens, but according to Bernard Burke of Massachusetts Institute of Technology, one of the group that first called these images an "apparent gravitational lens," the proponents of a gravitational lens are not giving up. Burke spoke in Ames, Iowa, at last week's meeting of the American Astronomical Society.

The two images lie 157 seconds of arc apart on the sky, and to Edwin L. Turner of Princeton (N.J.) University and his collaborators (including Burke), their spectra looked identical enough to be the same quasar. If that were so, the two images would be formed by bending of light around some very dense, massive object between us and them. One of the astrophysically exciting suggestions about the identity of that object is that it is a cosmic string, a kind of kink in space-time that is left over from an extremely early stage of the existence of the universe. Turner's group reported its conclusions in the May 8 NATURE.

Less than a month later, in the June 5 NATURE, P.A. Shaver and S. Christiani of the European Southern Observatory (ESO) headquarters in Garching bei Munchen, West Germany, reported observations of the spectra of 1146+111B,C in a range not covered by Turner's group. The work was done at the ESO at Cerro La Silla, Chile, and it seems to show that the spectra are not identical. In particular, certain lines that astrophysicists would expect in that range from a quasar of that particular class do not appear in one of the spectra. Shaver and Christiani suggest that the images are two different quasars very close to one another. (Both images are virtually the same distance from earth, so if they are not a double image, they must be close together.)

Also in the June 5 NATURE, under the rubric "scientific correspondence," E.S. Phinney and Roger D. Blandford of Caltech in Pasadena make a statistical argument for this to be two quasars close together and take it as evidence that quasars cluster as galaxies do. They call for a reexamination of the arguments on which other instances of alleged gravitational lensing are based.

Burke concedes that the finding of Shaver and Christiani is disturbing, but says "the issue is not settled." Further "careful, quantitative spectroscopy" of the two images and everything near them is needed, he says. That should start in October, when that part of the sky comes out from behind the sun.