PKS-1830-211 - A POSSIBLE COMPOUND GRAVITATIONAL LENS

Measurements of the properties of gravitational lenses have the power to tell us what sort of universe we live in. The brightest known radio Einstein ring/gravitational lens PKS 1830-211, while obscured by our Galaxy at optical wavelengths, has recently been shown to contain abso rption at the millimeter waveband at a redshift of 0.89. We report the detection of a new absorption feature, most likely due to neutral hyd rogen in a second redshift system at z = 0.19. Follow-up VLBI observat ions have spatially resolved the absorption and reveal it to cover the NE compact component and part of the lower surface brightness ring. T his new information, together with existing evidence of the unusual VL BI radio structure and difficulties in modeling the lensing system, po ints to the existence of a second lensing galaxy along our line of sig ht and implies that PKS 1830-211 may be a compound gravitational lens.