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Hot MamaHas matter’s motherpaid a call?

Physicists have found new signs that fieryparticle collisions within a giant accelera-tor two years ago created a state of matteridentical to what might have been the stuffof the newborn universe.

Stunning results announced this weekare prompting a growing chorus of physi-cists to say that it’s time to declare successin a decades-long quest to make quark-gluon plasma—an extremely hot, densesoup of matter that contains loose funda-mental particles known as quarks and glu-ons (SN: 8/26/00, p. 136).

“This really is a decisive moment,” saystheorist Miklos Gyulassy of Columbia Uni-versity. “I feel, at this stage, we’ve actuallyseen it.”

While mainly theorists take this stand,experimental physicists largely remain cau-tious.

Theorists have predicted that smash-ing together heavy atomic nuclei acceler-ated to nearly the speed of light can cre-ate a quark-gluon plasma. The resultingfireballs, which can reach temperaturesmeasured in trillions of degrees, areexpected to melt the protons and neu-trons that compose ordinary nuclear mat-ter. That process would briefly liberatethe quarks and gluons that make up pro-tons and neutrons.

Producing a quark-gluon plasmawould replay in miniature the criticalscene early in the cosmos when theplasma gave birth to ordinary matter,researchers say. Studying the plasma, sci-entists could expose the fundamentalnature of matter and the vacuum thatpermeates the cosmos.

In experiments conducted earlier thisyear, physicists at Brookhaven NationalLaboratory (BNL) in Upton, N.Y., smashedheavy gold nuclei with much lighter nucleicalled deuterons—the nuclei of deuterium,a hydrogen isotope. The researchers pro-duced those collisions in the lab’s Rela-tivistic Heavy Ion Collider, or RHIC—agiant device that is now the main tool in the

hunt for the quark-gluon plasma. Creating a quark-gluon plasma wasn’t

the aim of these experiments. The goal wasto determine whether observations fromearlier RHIC experiments could beexplained with theories that don’t summonthe quark-gluon plasma.

The new gold-deuteron tests focused onjets of particles emanating from the colli-sions. Jets are produced when two highlyenergetic quarks bounce off each other. Ifone or both escape the fireball, they breakup into sprays of other particles. Such jetsmay show up as single bursts or oppositelydirected pairs.

However, during the previous RHICexperiments, scientists had observed thatcollisions between pairs of gold nucleiyielded fewer jets than would be expectedat that collision energy.

Physicists had come up with two expla-nations for the discrepancy. In one scenario,if energetic quarks collide at a fireball’s edge,the quark heading away from the collision’scenter might get away while its partner bogsdown in the soup of still agitated, collidingparticles—the quark-gluon plasma.

Alternatively, some physicists sug-gested, a subtle property of nuclei knownas gluon saturation could have caused thejet suppression.

To sort out what was happening, theRHIC teams turned to the less energeticcollisions between gold ions anddeuterons. If gluon saturation were atwork, jet suppression would persist atthese lower energies. If not, jets wouldemerge in undiminished numbers becausethe gold-deuteron impacts generate toolittle energy to create a jet-absorbingquark-gluon plasma.

Jets weren’t suppressed, three inde-pendent RHIC teams announced Wednes-day at a BNL colloquium. The stunningimplication is that a quark-gluon plasmahad been present in the gold-gold experi-ments.

Nonetheless, most of the hundreds ofphysicists who have been conducting theRHIC experiments don’t consider the caseclosed, say members of those teams.Despite the new findings and other, pre-vious hints of quark-gluon plasma atRHIC, a stronger case will require observ-ing several additional features of collisiondebris to rule out some other form of hot,dense matter.

The experimentalists’ reticence stemsin part from fallout from an announce-ment 3 years ago by the European Labo-ratory for Particle Physics, or CERN, nearGeneva. Researchers stated that some-thing akin to the quark-gluon plasma, ifnot the plasma itself, had been producedin an accelerator there (SN: 2/19/00, p.117). To many other scientists, theannouncement gave the impression thatCERN researchers were prematurely

claiming discovery of the quark-gluonplasma when rigorous proof of such aclaim was still lacking. —P. WEISS

Stellar Top Astronomers find a squashed star

Think of the sun and other giant balls of gasthat twinkle in the heavens. Conventionalwisdom has it that all these stars are round.But because stars spin, they’re not perfectspheres. The rotation moves material out-ward more strongly at the equator than atthe poles. This nudges the star into a shapereminiscent of that of a toy top.

For a slow rotator like our sun, the effectis tiny. But for a rapidly rotating star suchas Achernar, which is 145 light-years fromEarth and six times the sun’s mass, that dis-tortion can be significant. Althoughastronomers already knew that Achernarspins at least 225 kilometers per second,they were flat-out astonished by theirnewest observations. The squashed star ismore than 1.5 times as wide as it is tall.

That makes Achernar the flattest starknown, report Pierre Kervella of the Euro-pean Southern Observatory in Santiago,Chile, and his colleagues in an upcomingAstronomy & Astrophysics.

Conventional models can’t explain sucha distortion, Kervella notes. In the simplesttheory, a star is assumed to be a solid ballwith its interior rotating more slowly thanits surface. But such a star would fly apartlong before it became as distorted asAchernar, says Marc H. Pinsonneault ofOhio State University in Columbus.

The only way Achernar can be so flat isif “the star is rotating much faster in the

OUT OF ROUND Artist’s rendition of thestar Achernar. The red arrow indicates thestar’s rotation axis.

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core than it is at the surface,” notes Pin-sonneault. The new data thus give “the firstpeek” inside a rapidly rotating star, he says.

The finding is “extremely interesting,”Pinsonneault adds, because a star whoseinterior turns more rapidly than its surfacewould mix the interior materials, produc-ing less-distinct layers than other stars have.According to models, the mixing wouldcarry metals forged at the core to the sur-face, enabling the star to more efficientlyseed the interstellar medium with heavyelements. At the same time, the churningaction would draw into the core a sur-rounding layer of hydrogen, a star’s mainfuel. This could double a star’s lifetime, Pin-sonneault says.

Gerard van Belle of the California Insti-tute of Technology in Pasadena cautionsthat instead of representing an intact, flat-tened star, the Achernar observations mayindicate a star that has exceeded its rota-tional speed limit and fallen apart, hurlinga disk of material from its equator. The diskmight be mistaken for a flattened star.

Kervella says his team’s spectroscopicobservations make that possibility highlyunlikely.

For their study of Achernar, the research-ers used a recently installed interferome-ter at the Paranal Observatory in Chile.Carefully combining the light from twosmall telescopes tens of meters apart, theastronomers achieved a resolution compa-rable to that of a single telescope the size ofa football field. —R. COWEN

Snake PitsViper heat sensors locate cool spots

Researchers who glued minuscule plasticballs onto the faces of live rattlesnakes saythe project has revealed the first experi-mental evidence of an overlooked role forthe viper’s heat-sensing organs. The newlytested function: finding places for the desertsnake to hide from the scorching sun.

Rattlesnakes can sense heat via specialreceptors sunk in two tiny pits on their faces,explains Aaron Krochmal of Indiana StateUniversity in Terre Haute. Decades of exper-iments have focused on how the pits enablethe animal to turn into a heat-seeking mis-sile for warm-blooded prey.

Now, Krochmal and George Bakken, alsoof Indiana State, report on the first tests of

whether the facial pits also help westerndiamondback rattlesnakes protect them-selves from overheating. After researchersblocked rattlesnakes’ facial pits, the animalshad trouble finding cool refuges, Krochmaland Bakken report in the Aug. 1 Journal ofExperimental Biology.

Bakken says that experiments on seekingrefuge may help ecologists learn how ani-mals deal with a patchy environment.

Krochmal adds that the need for ther-moregulation may have driven the evolu-tion of early pits and the snakes’ spectacu-lar prey targeting came later.

When Krochmal decided to test rat-tlesnakes, he hadn’t ever handled poison-ous snakes. He practiced for months witha harmless but cranky black rat snake. Still,he says, “the first time [working with a rat-tlesnake] was the most unnerving experi-ence of my natural-born life.”

First, he tested 12 wild-caught snakes ina simple Y-shaped tube with one branchkept comfortably cool at 30°C and the otherheated to a stressful 40°C. Snakes put intothe Y’s stem, also at 40°C, slipped into thecool end about 75 percent of the time.

Then Krochmal anesthetized all thesnakes and blocked their 2-millimeter-widefacial pits with tiny plastic balls and alu-minum foil temporarily glued on top. Snakeswith blocked pits ended up in the cool spot

only half the time, as if by chance. WhenKrochmal unblocked the pits, though, thesnakes’ performance bounced back.

The researchers repeated this test with achoice of four boxes, one of them cool, andthen with four natural-looking burrows.Each time, the snakes’ performance dippedwhen their pits were blocked but bouncedback when the paraphernalia came off.

Snake specialist Harry Greene at CornellUniversity asks how well the test setups,where there’s less than 1 meter from asnake’s decision point to the cool nook, rep-resent choices in the real world. He sug-gests yet another important use for the pits:assessing danger from predators. However,he says that the idea that facial pits evolvedfor body-temperature control “deservesserious consideration.” —S. MILIUS

Lithium Seesthe LightImages of tiny ion mayhelp battery designers

Hidden within cell phones, laptops, anddigital cameras, lithium-ion batteriesincreasingly power the world. For the first

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HEAT TEST A western diamondback rattlesnake lost its skill at spotting cool refuges whenresearchers blocked its heat-sensing pits with tiny balls and aluminum foil (inset).

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