Einstein's Cross

by Jay Reynolds Freeman

Who's Afraid of Einstein's Cross
Fun with Einstein's Cross - by Ray Cash

Central California's record warm temperatures a few days before the 1998 winter solstice struck terror into the hearts of those who believe that the "law of averages" is the result of malevolent manipulation by malicious nature. Sure enough, the following weekend produced a cold snap and a hard freeze. Sunday morning saw snow, sleet, and hail down to sea level. Unfortunately for diehards, Saturday night was clear, so we had to go out and observe.

Fremont Peak temperatures were dropping fast toward freezing, and a moderate breeze drove wind-chill far lower, as I set up Harvey, my Celestron 14. Notwithstanding, the optical tube assembly was well thermally equilibrated by the time I was ready to observe: The time I spent sitting in the car, with the engine running and the heater on fricassee, was put to purposeful use. Wanting to look at some good stuff before my enthusiasm chilled out, I found rho and sigma Pegasii in the finder, not far from the southwest corner of the Great Square, then worked my way five or six degrees further south and west, to the field of Einstein's Cross.

With my 40 mm Vernonscope Erfle eyepiece delivering 98x, the mass that forms the gravitational lens whereby this object is imaged was not difficult to see, but after all, it is relatively nearby. The galaxy responsible is too faint to have an NGC or IC number, but CGCG 378-15 -- for that is one of its several catalog labels -- is nonetheless fairly easy for fourteen inches of aperture. And four hundred million light years is pretty close. Why, not only was there multi-celled life on Earth when that chilly evening's photons left home, there were even critters that a generous soul might have called vertebrates. Yet the quasar whose light is refocused by this prominent piece of lumpy darkness is much farther off -- CGCG 378-15 is acting as a long, long-distance microscope. [Image: Einstein's Cross (HST)]

At 98x I could not see any real sign of the cross, though it was clear that the galaxy became rather rapidly brighter at the middle. I wasn't surprised, for the structure is small and faint -- only a few arc seconds wide -- and the galaxy itself provided a background of light pollution more than sufficient to hide it. Fortunately, there was a fix that did not require litigation by the Intergalactic Dark-Sky Association -- jam on the magnification -- and I did exactly that. Replacing the big Erfle with a 12 mm Brandon gave 326x, and spread out the faint smudge of the galaxy sufficiently to render it completely invisible.

So I promptly got lost. Between jiggling the telescope when I changed eyepieces, occasional wind shudders, and the usual confusion about which control-paddle button moves things which way and where did they put north this evening anyhow, I soon found myself half a degree or more from the target, with no hope of getting back.

Humph! Back in went the Erfle, and back I went to the finder to reacquire the field. Oh... there it is... double humph! It took several eyepiece switches between the Erfle and the Brandon, and a good deal of practice, star-hopping from several prominent and easily recognizable stars out to where the galaxy was, before I could set on it confidently at the higher magnification. Furthermore, I had to swap eyepieces several times more, to verify the positions of a few much fainter stars that were confusing me. Finally I established to my satisfaction that I had the center of CGCG 378-15 in the center of my 326x field. And what do you know -- there was something there.

The figure of the giant gravitational lens is less than perfect. The image of the distant quasar is not a good representation of the object itself; rather, there are four bright lobes distributed symmetrically around a central point, rather like the wide ends of a cross whose arms have equal lengths. Many of us have seen the images of stars similarly made complicated by poor seeing, and some of us have encountered optics that can create such views even when the air is steady. CGCG 378-15 is such an optical system. [Image: the lensing galaxy at high power (DSS)]

I cannot claim to have identified the separate sub-images individually, resolved from one another as if they were components of a faint double star. Indeed, much of the time I could not see anything at all -- seeing jitter did not permit continuous observations at 326x. But when seeing steadied, it was clear that there was a small structure at the heart of the galaxy, just a few arc-seconds across, and I could tell that it had an irregular shape. I don't think there is much doubt that I was seeing the combined lobes of Einstein's Cross. It would be fun to reexamine the object on a night of truly fine seeing, perhaps with more magnification. I suspect that Harvey is capable of showing it with a little detail.

Most of the reports of seeing Einstein's Cross that I know of, have involved Dobson-mounted Newtonians with apertures substantially larger than 14 inches, and some extremely good observers have had trouble seeing more than one or two of the lobes of the cross at those apertures. Therefore, I wish again to stress that I did not see any of the components separately -- in double-star terms, I had an elongation (actually, several), not a split. I should also mention that it certainly helped to have a driven telescope, so that I could sit in comfort -- well, in what would have been comfort if I hadn't been a bit chilly -- waiting for the seeing to steady, and trying to use averted vision in just the right way, rather than having to jiggle a big Dobson from the top of a tall ladder, while an elusive and all but invisible object dashed pell-mell for the far horizon.

Yet what a thing to see, even if only at the limit of visibility. The quasar whose image forms the cross is some eight billion light years away. The photons I saw left their source long before our solar system was formed, probably long before most of its heavy atoms were even synthesized. When they originated, everything we now see about us was for the most part primordial star-stuff, hydrogen atoms formed in the Big Bang, awaiting nucleosynthesis in suns now long dead, followed by redispersal into the void as planetary nebulae or supernova remnants. One day a few of them, now mere animate debris left over from the condensation of a younger and smaller star, would look back into the abyss, seeking a far-off, distorted glimpse of what the cosmos was like when they were young, and wondering how it would all turn out when they were old.

Such is Einstein's Cross.