The quest for the golden lens: a perfect alignment of massive objects would offer clues to the rate of cosmic expansion

With the orbiting Chandra X-ray Observatory, Raychaudhury and his colleagues found that the lensing object wasn't a single galaxy, but rather an entire group of galaxies, whose distribution of mass was relatively smooth and uncomplicated--one key requirement for a golden lens. Raychaudhury created 300 possible models of the shape of the lens, and simulated the lensing properties of each model. From the simulations he calculated the time delays that would result.

Unfortunately, the simulations showed that only two of the four images would yield measurable time delays. Moreover, one of those two images is too faint for its brightening to be feasibly measured with current technology. The conclusion: B1422+ 231 is indeed a fascinating gravitational lens system, but it's not quite golden.

As with most quests, Jason's journey was much more interesting than the reward at its end. "What became of the fleece afterwards," wrote the nineteenth-century American writer Thomas Bulfinch, in his classic Mythology, "we do not know, but perhaps it was found after all, like many other golden prizes, not worth the trouble it had cost to procure it."

Rest assured, though, that if a golden lens is found, it will retain its value. We astronomers will monitor its flickering year after year until it yields a firm, independent measurement of the Hubble constant. And we won't stop at one such lens; we'll study every golden lens we can find, to cross-check our results. The Argonauts' odyssey ended long ago, but this cosmological golden quest has only just begun.

Charles Liu is an astrophysicist at the Hayden Planetarium and a research scientist at Barnard College in New York City.

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