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From: allan@noao.UUCP
Newsgroups: net.physics,net.astro.expert
Subject: Re: quasars and the history of the universe
Message-ID: <345@noao.UUCP>
Date: Fri, 25-May-84 12:22:26 EDT
Article-I.D.: noao.345
Posted: Fri May 25 12:22:26 1984
Date-Received: Fri, 1-Jun-84 05:35:15 EDT
References: <2440@brl-vgr.ARPA>
Organization: Natl. Optical Astronomy Obs.  Tucson AZ USA
Lines: 24

Yes there are multiple images of the lensed quasar. There are two images 
about 7 arcseconds apart on the sky and are about 17th magnitude. 
According to the theory, there has to be an odd number of images if a
distributed object such as a galaxy is doing the bending. The idea is that
there are three images, but that two of them are so close together that they
appear as a single object. As well as the optical information on the double
quasar, there are also radio maps which show the double structure. The two
images have been seen to vary, but they do not vary together. There is the hope
that by monitoring the quasars over many years that it will be possible to
correlate the variability and so find the difference in the light travel time
along the two paths to the quasar. Knowing this and the geometry of the
situation, we can measure the TRUE distance to the quasar. If this can be done
then it will give us the value of the Hubble constant since we know the redshift
and the variations give the distance. The problem with this is that so far we
are not too sure about the geometry as there is a cluster of galaxies associated
with the lensing galaxy, and this cluster provides a significant lensing effect.

There are (I think) 4 more examples of multiple quasars. PG1115+080 is a triple
quasar, just like the theory predicts.


Peter (theories to go) Allan
Kitt Peak National Observatory
Tucson, Az