Glass mav ma& ultrasmll-world oddities The strange rules of quantum mechan-

ics apply mainly to the atomic and sub- atomic domains. Only rarely do those rules manifest themselves on a larger scale, as in the case of superconductors, which let electricity pass without resist- ance. Physicists prize phenomena such as these because they offer a sometimes bizarre, bigscreen picture of quantum me- chanics in action.

Now, European researchers report that they may have discovered a thoroughly unexpected example of large-scale quan- tum behavior. It takes place in ultracold samples of certain types of glass. The ex-

perimenters stumbled upon it while try- ing to improve on low-temperature ther- mometers by using glasses whose capaci- tance, or ability to store charge, varies with temperature.

The investigators expected magnetic fields to have negligible influence on ca- pacitance readings for the glass. To their surprise, magnetic field variations affect- ed the measurements 10,000 times more strongly than anticipated.

“These are very strange experimental results, indicating very new physics,” says Christian Enss of the University of Heidelberg. The outsize response to mag-

Tidal tails tell tales of newborn galaxies Talk about big-time mergers. In the in-

fant universe, marauding galaxies de- voured each other, coalescing to form big- ger galaxies. These hostile takeovers spewed out truly hot commodities-gas and dust that could become the ingredi- ents for nascent stars.

A similar process may still be unfold- ing. Whenever two galaxies come close enough, their mutual gravity rips long streamers of gas and dust from each oth- er. Some of these so-called tidal tails may become galaxies in their own right, un- dertaking the same evolution that their ancestors did billions of years ago.

A new study adds to the evidence that some tails containing young stars are in- deed small galaxies in the making. Study- ing two tails torn from different pairs of mature galaxies a few hundred million light-years from Earth, Jonathan Braine of the Bordeaux Observatory in France and his colleagues argue that both tails cook up their own molecular hydrogen-the raw material for making stars-rather than steal the stuff from their parents. The researchers describe their observa- tions in the Feb. 24 NATURE.

If the results hold, they “would offer astronomers the exciting prospect of studying up close a potentially impor- tant galaxy-formation process,” says Gary Welch of Saint Mary’s University in Halifax, Nova Scotia.

Braine and his colleagues examined the tails with the Institut de Radioastronomie Millimetrique’s 30-meter radio telescope. atop Pic0 Veleta in Spain. Because molec- ular hydrogen emits little radiation, they traced the molecule by hunting for emis- sions from a companion molecule, carbon monoxide. In both tails, the team found the highest concentrations of molecular hydrogen where densities of atomic hy- drogen were highest.

This suggests that most of the molecu- lar hydrogen was not simply torn off the parent galaxies, as the atomic hydrogen was, because the molecular and atomic forms typically have very different distri-

MARCH 4,2000

The tug of war between two galaxies (lee) has created two tidal tails (arrows). Inset shows the lower tail, indicatihg locations of atomic hydrogen (white contour lines) and carbon monoxide (faint red circle).

butions in such galaxies. Molecular hy- drogen tends to cluster at the center of a mature spiral galaxy, whereas atomic hy- drogen spreads out.

The observations suggest that the tails are making fresh molecular hydrogen from atomic hydrogen, Braine and his colleagues argue. “Star formation in the tidal dwarf galaxies therefore appears to mimic the process in normal spiral galax- ies like our own,” the researchers say.

Although other astronomers have de- tected carbon monoxide in tidal tails, those tails didn’t appear to be making stars. “Until this paper came out, there wasn’t any clear detection of molecular gas in something that looked like it might be forming a galaxy,” says Welch.

Rosemary F.G. Wyse of Johns Hopkins University in Baltimore says that dwarf galaxies formed from tidal tails would have a proportion of dark matter-the unseen material that makes up 90 percent of the mass of the universe-similar to that in large, spiral galaxies like the Milky Way. That would distinguish them from the many dwarf galaxies known to have a much greater dark matter content. -R. Cowen

SCIENCE NEWS, VOL. 157

netic fields starts to kick in below about 100 millikelvins (mK) and is stronger at much lower temperatures, report Enss, Peter Strehlow of the Physikalisch-Tech- nische Bundesanstalt in Berlin, and their colleagues in the Feb. 28 PHYSICAL REVIEW LETTERS.

The researchers discovered that below 5.84 mK, a critical temperature at which the response intensifies, even magnetic fields a hundredth as strong as Earth’s weak field alter glass capacitance.

“I find this work extremely exciting,” says Douglas D. Osheroff of Stanford Uni- versity. “I don’t know if I would call this a new quantum phenomenon, but it is cer- tainly very interesting.”

Working with the experimenters, some theorists have come up with an explana- tion for the magnetic response. They make use of an idea developed in 1972 that attributes certain properties of the glasses to the motion of particles-proba- bly ions or ion clusters-via the quantum effect called tunneling. Chilling the glass quells heat-related jitters of its ions enough for tunneling motions to become coordinated, the new theory proposes. The ions’ synchronized movement gener- ates a magnetic field, which interacts with external fields.

Above 5.84 mK, synchronization occurs only in patches a few micrometers across. Below that temperature, the theorists say, all the sample’s ions abruptly fall into the same quantum mechanical state. Similar- ly, atoms in a Bose-Einstein condensate (SN: 7/15/95, p. 36) and electrons in a su- perconductor share a single state.

Stefan Kettemann and Peter Fulde, both of the Max Planck Institute for Complex Physical Systems in Dresden, and Strehlow described that theory in the Nov. 22,1999 PHYSICAL REVIEW LE~TERS.

Although the newly reported data seem to indicate a “real effect,” Anthony J. Leggett of the University of Illinois at Ur- bana-Champaign argues that impurities that have intrinsic magnetism might ac- count for it.

Enss says the researchers ruled that out by determining that the glass con- tains too few magnetic impurities to have an appreciable effect.

A skeptical Philip W. Anderson of Princeton University, who helped devise the 1972 tunneling theory, says that re- searchers have yet to identify what enti- ties do the tunneling-ions, groups of ions, or something else. “What kinds of conclusions can you draw about ‘a riddle, wrapped in a mystery inside an enigma’?” he asks, quoting Winston Churchill.

Enss concedes that the presence of a large-scale quantum state in glass below 5.84 mK remains unproven. He and his coworkers have begun experiments to test for definitive evidence, such as inter- ference effects between samples. “There might be other explanations [than large- scale quantum effects],” he says, “but so far there isn’t one.” -P Weiss

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