Galactic data shore up a constant

From Tampa, at a meeting of the American Physical Society

The first galactic test for possible variations in a fundamental constant of nature has found no evidence for change. The new findings raise doubts about a 2001 report by quasar observers that alpha, a presumed constant that figures into the strength of the electromagnetic force, actually varies over time, says Jeffrey Newman of Lawrence Berkeley (Calif.) National Laboratory.

The earlier observations examined absorption of quasar emissions by clouds of gas deep in space, and the findings suggested that alpha, also called the fine-structure constant, has grown slightly since the universe was young (SN: 10/6/01, p. 222: Constant Changes). Any fluctuation could have big implications. For instance, a changing alpha might signify extra unseen dimensions.

The new galaxy data gathered by Newman and his colleagues emerges from DEEP2, a nearly completed 5-year telescope survey of thousands of distant galaxies. To test alpha, DEEP2 scientists monitored light of two specific wavelengths coming from oxygen ions in 300 of the brightest galaxies in the survey.

When the universe was about half its current age, ultraviolet radiation from the galaxies’ stars excited oxygen ions in gas clouds within the galaxies. Those ions then emitted the light now reaching Earth, Newman explains. If alpha had changed since the original emission, the wavelengths emitted by oxygen ions on Earth today would differ slightly from those coming from the faraway galaxies.

As it turns out, the observed wavelengths have remained the same—to a precision of one part in 30,000—according to a comparison of survey data with laboratory spectra of oxygen ions, Newman reports.

However, it’s too early to draw firm conclusions from the new study, he cautions. For one thing, the 2001 quasar study yielded an alpha variation of one part in 100,000—too subtle for the new galaxy study to detect or rule out.

Moreover, quasar data like those in the earlier study have grown and still support a changing alpha, says astronomer Michael T. Murphy of the University of Cambridge in England. “Now, we have a sample of [quasar observations] nearly three times the sample in 2001,” Murphy told Science News.

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