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From: jlg@lanl-a.UUCP
Newsgroups: net.physics,net.astro.expert
Subject: Re: quasars and the history of the universe
Message-ID: <7790@lanl-a.UUCP>
Date: Wed, 23-May-84 22:50:35 EDT
Article-I.D.: lanl-a.7790
Posted: Wed May 23 22:50:35 1984
Date-Received: Thu, 31-May-84 20:05:50 EDT
References: <2156@brl-vgr.ARPA>, <339@noao.UUCP>
Organization: Los Alamos National Laboratory
Lines: 16

i

I think that the original submitter of the pulsar-quasar mix-up was referring
to the periodic variation in quarar magnitudes.  I don't remember details but
I think that this variation is somewhat irregular.  The problem is that the
approximate period of the variations is short (on the order of hours). No
known mechanism (rotational or otherwise) can produce regular variations
of period shorter that the light travel time across the object.  Yet the 
diameter of quasars must be larger than a few light-hours if they are really
far away.     

The thing is, quasars (at least one) is very far away indeed!  There is an 
example of a galaxy (fairly distant itself) which acts as a gravitational
lense and bends the light from a quasar behind it.  Seems like the quasar has
to be significantly further away than the galaxy for this effect.