Beyond the Hubble Sphere (was: Re: Einstein's Cross)

I've looked at Einstein's Cross a few times in the 30" at Fremont Peak. I've
probably tried for it in my 18", too. Being in or near Pisces, IIRC, it's a
decent Calstar target if the seeing is good.

I don't have my notes in front of me, but to the best of my memory, I've
gotten it to look somewhat less `stellar' than the faint field stars around
it. Thus, it's clearly a different sort of object than the field stars, but
I've never been able to see the four `sub-members' at once. During the very
best moments of seeing, I thought I had the impression that one or another
of the lensed images was popping in to view, but I never felt that I was
seeing more than one at once.

It definitely deserves its reputation as a very difficult object!

I'll second Steve's recommendation of the Double Quasar in UMa. I've split
that with the 30"; can't recall if I've tried to do so in anything smaller.
Seeing gravitational lensing is pretty darn cool.

Anytime we're on the topic of observing distant quasars, I always think of
the topic of `how far can you see?', which was well-addressed by David
Kingsley in 2002:

http://www.observers.org/tac.mailing.list/2002/Sep/0712.html

A Google search shows that I've posted about the following topic before
(Dec. 7, 2009), but a quick look at the archives doesn't show my message...
hmmm, maybe I'm missing something... but since we're talking about
high-redshift objects, I think that the following paper is a must-read:

http://lanl.arxiv.org/abs/astro-ph/0310808

This paper explains how, in the current `Lambda-CDM concordance' model for
the universe, which is observationally well-constrained (e.g. by WMAP), z =
1.46 is an important redshift. If you manage to observe an object with z >
1.46, you're seeing light from an object that is receding from us faster
than the speed of light. It's beyond a portion of the universe called the
`Hubble Sphere'.

Yes, it's possible for objects to have an apparent velocity of recession
greater than light. Even much greater. And no, this doesn't violate
relativity. That's what the paper is all about. It also points out that many
textbooks and popular accounts of cosmology are filled with inaccuracies and
misconceptions about the expansion of the universe, including assertions
that nothing can appear to recede from us faster than light. It's well worth
a read.

-Marek Cichanski

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