Expanding a theory for shifting starlight.

Expanding a theory for shifting starlight

If Oscar Peterson were running alongside a speeding Ella Fitzgerald as she belted out an A, he would hear an A. But if the pianist took a breather while singing Ella raced on, the Doppler effect would make the note sound lower to him.

For close to a century, scientists have known that the wavelengths of light from a rapidly receding source in out space also get Doppler-shifted to lower frequencies and so appear redder than they would if their source remained stationary. Moreover, researchers have assumed that this so-called redshift can result only from Doppler motion or from a gravity-based mechanism also uncovered early this century.

Not so, contends physicist Emil Wolf of the University of Rochester (N.Y.). In 1986, he published a theoretical sketch of a third mechanism that could account for part of the redshift of light from exotic cosmic objects such as quasars. Several researchers have since reported laboratory confirmations of the process, which some of them refer to as the "Wolf shift" (SN: 9/13/86, p.166; 7/11/87, p.22).

Now Wolf reports an important extension of his theory, suggesting the process could account for arbitrarily large shifts toward either the red or blue end of the electromagnetic spectrum.

In its earlier form, the theory proposed a mechanism that could produce small redshifts in the spectra of light emitted from certain exotic sources. Wolf suggested at the time that the shifting mechanism could emerge physically from partially synchronized, or coherent, fluctuations in the wavelengths of light emitted from the countless individual atomic and molecular "microlamps" that make up such a source. As these emissions travel through space, their original spectrum would appear to shift in the same way as Doppler-shifted light.

Though its astronomical consequences remain unknown, the theory could change estimates of the size of the universe and help explain some anomalous astronomical observations, Wolf says. However, astronomers have not rushed to adopt it. No known light source has components that display the required correlated fluctuations, Wolf notes. He also blames the theory's unorthodoxy and its arcane mathematical formulation for its limited consideration by astronomers.

In the updated theory, described in the Nov. 13 PHYSICAL REVIEW LETTERS, Wolf outlines a more general -- and perhaps physically more plausible -- mechanism that could imitate Doppler shifts of any magnitude. Instead of requiring the microlamps in the source to fluctuate in some correlated fashion, he now proposes that a complex "scattering medium," such as the electrically charged and frenetic atmosphere thought to surround quasars, might serve as an unusual lens that restructures incoming light to have redshifting or blueshifting correlations upon leaving the medium. "A scattering medium of the right type between the source and an observer should produce these effects," Wolf told SCIENCE NEWS

Wolf concedes that astronomers have never reported such a scattering medium and notes that he used simplifying assumptions in both the original and updated theories. Nonetheless, the expansion of the theory strengthens the case for a third physical mechanism underlying spectral shifts even in light from stationary sources. University of Rochester astronomer Malcolm P. Savedoff says the soundness of Wolf's theory demands that scientists take it seriously. In a paper submitted to ASTROPHYSICAL JOURNAL, Savedoff, Wolf and graduate student Daniel F.V. James have mathematically modeled scattering media that are consistent with typical models of the environment near quasars.