Magnetic studies may pose cosmic puzzle.
The new studies focus on radio-wave jets emitted by quasars. As they travel through space, the jets pass through galaxies, gas clouds and other material. Such objects make their location known by absorbing specific wavelengths of light, leaving telltale gaps in the spectra of quasar light that reaches Earth. Magnetic fields make their presence, though not their location, known in a more subtle way; They alter the polarization of light--that is, the direction in which the electric field of a light wave vibrates as the wave heads toward an observer.
In 1983, Judith J. Perry of the University of Cambridge in England and Philipp R. Kronberg of the University of Toronto began studying a radio jet from a quasar called Parkes 1229-021, which lies about 6 billion light-years from Earth. Using the Very Large Array radiotelescope near Socorro, N.M., to scan the width of the jet at high resolution, they found something strange. Across the jet, the polarization of radio waves had been altered--some had their electric field twisted to the right, some to the left, in a repeating pattern.
That polarization pattern mimics those produced by magnetic fields found in some spiral galaxies near the Milky Way. After observing the jet's polarization at seven different wavelengths, Perry and her colleagues concluded that the strength of the inferred magnetic field matches that of the Milky Way and some of its neighbors. But there's a catch. The researchers propose that the culprit that altered the radio jet is an unseen galaxy residing some 4 billion light-years from Earth--nearly halfway to the edge of the observable universe.
If the distance estimate proves correct, the work may have major implications, Perry says. First, the radio observations indicate that the team may have mapped the large-scale magnetic structure of a galaxy 200 times farther away than any mapped previously. Second, the study suggests that the magnetic field strength of the young galaxy, measured as it appeared billions of years ago, equals that of the present-day Milky Way. Perry, Kronberg and University of Toronto colleague Edwin L.H. Zukowski report their work in the March 10 Astrophysical Journal.
Their results, not the researchers, hinge on a key assumption. The absorption spectra of light from the quasar indicate that a galaxy lies in the jet's path about 4 billion light-years from Earth. Based on studies with other quasars, it seems statistically likely that such a light-absorbing object harbors the magnetic field mapped by her team, Perry says. But she cautions that the field might belong to another celestial object, even the quasar itself. No one has yet observed the proposed galaxy, Perry notes, possibly because the quasar's light masks the dim emissions from the body.
Though speculative, the study's conclusions agree with results of an ongoing quasar survey that Arthur M. Wolfe and his colleagues at the University of California, San Diego, will report in the March 20 Astrophysical Journal. They examined, though in less detail, the polarization of quasars more distant than the one studied by Perry's team. Wolfe found indications that young galaxies far more distant than the one Perry proposes--dating to the time when the universe was just one-tenth its current age--nonetheless had magnetic fields as strong as the Milky Way's. Such youthful galaxies did not have enough time to build up big fields from extremely tiny ones, Wolfe says. The findings, he adds, suggest that even at its very beginning, the universe harbored magnetic fields of considerable strength.
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|Date:||Mar 14, 1992|
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