Gravity Ripple


Ripples of space-time debut

in black hole simulation

When black holes collide, they cause surrounding space-time to wiggle, thus generating a torrent of radiation known as gravitational waves. That’s what Einstein’s general theory of relativity predicts, but computer models have struggled for more than 30 years to reproduce those waves. Because of the relativity theory’s mathematical complexity and the extreme gravity of black holes, modelers hadn’t succeeded in getting black holes to crash. Instead, the computer programs did.

Now, two teams independently report that they have successfully simulated the merger of two black holes and the event’s production of gravitational waves.

“This is a breakthrough not only in numerical relativity, but it is a necessary step in preparing us to observe gravity waves, comments theorist Stuart Shapiro of the University of Illinois at Urbana-Champaign. “It’s also the first serious link between cosmology and the merger of black holes:”

Observers have begun searches for gravitational waves using several ground- based networks..A space-based detector is scheduled for launch early in the next decade. The waves described by the new simulations “are telling the detectors what to look for,” says Carlos Lousto of the University of Texas at Brownsville. Lousto and his colleagues, as well as a group led by John Baker and Joan Centrella of NASA’s Goddard Space Flight Center in Greenbelt, Md., describe some of their work in the March 24 Physical Review Letters. Both groups also report new simulations in an upcoming Physical Review D.

Modelers had previously simulated gravitational waves produced by colliding neutron stars, which are city-size balls of neutrons. But colliding black holes presented more of a problem. The gravity of such a monstrous pair squeezes space-time to a point that has infinite density, the so-called singularity that a computer program has

Some researchers, including the teams led by Baker and Lousto, deal with the singularity by isolating it “into a corner of the computer grid never seen by the computer code,” explains Shapiro. “Most people who might have thought about this new method were afraid to try it,” he says. That strategy seemed destined to fail, says Shapiro, because people thought, “you can run [from a singularity], but you can’t hide:”

Nevertheless, the simple approach enabled the modelers to watch the gravitational waves emitted by two orbiting, equal-mass black holes in the critical period hours or seconds before they coalesced. Newer work by the Goddard team focuses on black hole collisions in which one of the bodies is heavier than the other. In such unequal-mass collisions, gravitational waves are concentrated in a specific direction, propelling the merged body in the opposite direction.

Such kicks might have played a crucial role in the growth of supermassive black holes when the universe was about half a billion years old. The center of nearly every new galaxy back then probably housed a fledgling black hole. Collisions between two unequal-size black holes could have generated a gravitational-wave kick big enough to eject each member of the pair from its home galaxy, making unlikely any further growth of those black holes or their galaxies. The strength of the kick revealed by the Goddard simulation su ests that gravitational waves could indeed have controlled the growth of black holes and galaxies.

The findings shed light “on a huge cosmological problem of how.. ... supermassive black holes in galaxies grow into bigger ones,” says Shapiro.




April 22, 2006 Vol. 169. No. 16 Pages 241-256.

1719 N. St., N. W. Washington, D. C. 20036


Science news

Electric spectacles could aid aging eyes.

A NEW TYPE OF EYEGLASSES with electrically adjustable focus might someday render bifocals and reading glasses obsolete, the device’s inventors say. So far, the researchers have made a battery-powered prototype with close-up focus that flicks on and off with a switch.

Future versions of the eyeglasses may incorporate a distance sensor to automatically adjust the focus as the viewer’s gaze changes between far and near viewing, says one of the inventors, electrical engineer David L. Mathine of the University of Arizona in Tucson.

Most people by their late 40s can no longer focus on close objects. This visual defect is known as presbyopia. The company PixelOptics of Roanoke, Va., plans to create a commercial version of the electrically adjusted eyeglasses to market to presbyopic people, who typically wear bifocals, trifocals, or graded lenses. Worldwide, about 50 million people per year become presbyopic, according to the comp-any’s Web site.

In bifocals, some portion of the lens remains unfocused for the distance of interest at any given time, notes Mathine. In the new eyeglasses, the entire lens switches to the desired focus. For close vision, for instance, “you don’t have just the bottom half of your eyeglasses. You get the whole view.” he says.

To make eyeglass lenses that change focus electrically, the researchers created sandwiches of glass sheets separated by a fluid layer 5 micrometers thick. The filling consists of a transparent substance, a type of liquid crystal, that’s made up of rod- shaped molecules suspended in a liquid. The team used precise computer-chip —manufacturing methods to apply a bull’s-eye pattern of transparent electrodes to the inner surface of one of the glass sheets.

In response to voltages applied to those electrodes, the liquid-crystal rods rotate into new orientations, explains Guoqiang Li of the University of Arizona and a member of the development team. The rod orientation determines the speed at which light passes through the liquid-crystal layer. Light rays bend as they traverse the layer and so can become focused, much as they would when passing through an ordinary lens.

The researchers describe the new eye-glasses in the April 18 Proceedings of the National Academy of Sciences.

In the past, other scientists have made electrically controlled lenses from liquid crystals—using them, for instance, to steer laser beams or to alter the focus of a reader used in optical-memory devices. However, previous liquid-crystal lenses could neither focus well enough nor change their focus quickly enough for use in eye glasses, Li says.

The newly developed lens is “the only adaptive lens that is practical for presbyopia patients;’ says biomedical and optical engineer Shuliang Jiao of the University of Miami (Fla.) School of Medicine, who didn’t participate in the research.

PixelOptics plans to create a version of the glasses that will enable people to have better than normal 20/20 vision, says physicist Dwight P. Duston, head of research and development for the company.




Babies conceived 18 months to 5 years after a previous birth are much healthier than those conceived at shorter or longer intervals, a massive data analysis shows.

Studies to determine the optimal spacing between a birth and the mother’s next pregnancy have yielded mixed results . In an attempt to settle the question, researchers in Colombia analyzed 67 studies that included more than 11 million births worldwide.

Compared with babies conceived 18 to 23 months after a sibling’s birth, those conceived within 6 months were 40 percent more likely to be born prematurely, 61 percent more likely to be underweight (less than 2.5 kilograms, or 5.5 pounds), and 26 percent more likely to be small for their gestational age at birth. Babies conceived between 6 and 17 months after their mothers’ previous birth also had a slightly increased risk of the three health measures whereas babies conceived 24 to 59 months after a previous birth had no increased risk.

Premature birth, low birth-weight, and small size for gestational age are all risk factors for poor health in infancy and can lead to complications later in life.

Health officials should counsel women who’ve just given birth to delay their next conception by 18 to 59 months, concludes study leader Augustin Conde-Agudelo of the Santa Fe Foundation in Bogota.

“This is the first, and certainly the most ambitious, attempt to do this sort of rigorous meta-analysis” of the birth interval, says physician C. Johannes van Dam of the Population Council in New York City.

Curiously, babies conceived 5 years or more after a birth were 20 ,29, and 43 percent more likely to be premature, small for gestational age, or underweight, respectively, than were the babies conceived after 18 to 23 months, the researchers report in the April 19 Journal of the American Medical Association.

It’s unclear why a long interval would impart such risks.

The problems of a baby born after a short interval are better understood. The second baby might suffer because the mother is nutritionally depleted and physically stressed by simultaneously recovering from the first birth, handling an infant, and carrying a new fetus, van Dam says.

Epidemiologist Mark A. Klebanoff of the National Institute of Child Health and Human Development in Bethesda, Md., questions whether getting pregnant soon after a birth is the primary factor that places a pregnancy at high risk. “Is there something about women who get pregnant right away that imparts the risk? he asks.

He cites earlier research showing that women with very long or short birth intervals are more likely to be unmarried and have less education than other women. Although Conde-Agudelo’s team tried to account for these and other differences, many of the studies in their analysis relied on birth certificates, which, Klebanoff says, are notoriously incomplete and inaccurate.”

Worldwide, roughly half of all births are unplanned. Doctors should counsel new mothers against having another child right away, van Dam says. The best results will come in countries with birth control programs and prevalent breast-feeding, which naturally delays a woman’s return to fertility.



Perception narrows toward infancy’s end

Rather than crawling inexorably toward a better appreciation of the world around them, infants take a perceptual step back-ward before their first birthday, a new study indicates. That reversal, ironically, paves the way for advances in thinking later in childhood.

When shown videotapes of monkeys’ faces that either matched or clashed with the sounds being made by the animals, 4- and 6-month-olds preferred to look at just matches, whereas 8- and 10-month-olds displayed no preference, say David J. Lewkowicz of Florida Atlantic University in Boca Raton and Asif A. Ghazanfar of Princeton University. Looking preferences in the younger babies denoted an awareness of associations between faces and vocalizations, the researchers assert.

Younger infants probably noted when facial movements were synchronized with vocalizations, the two psychologists assert in the April 25 Proceedings of the National Academy of Sciences. The older infants ignored the basic phenomenon of synchrony because they had entered a phase of looking for more-complex features of human faces and voices, the scientists propose.

“We’re tapping into a transition period in late infancy when ... it’s more difficult to perceive links between different sensations;’ Lewkowicz says. Constrictive phases characterize development of various types of perception, in his view.

For instance, other researchers have found that, between 6 and 10 months of age, infants improve at discriminating among sounds in their native languages and also among different people’s faces. During that same time, youngsters become worse at telling apart foreign-language sounds and other species’ faces, such as those of monkeys.

Lewkowicz and Ghazanfar suspected that a comparable form of perceptual narrowing occurs as babies learn about critical relationships between different sensations, such as sights and sounds. The experiment consisted of 33 infants at 4 months of age, 57 at 6 months, 54 at 8 months, and 32 at 10 months.

Each baby sat in front of two adjacent video monitors, and completed four 1-minute trials. Flashing lights drew each infant’s attention to the monitors as pairs of video’s showed monkey’s faces making either coo or grunt calls. Characteristic lip and facial movements for each call were accompanied either by the sound of the same call or by the sound of the other call.

At the two youngest ages, infants looked substantially longer at faces that made matching calls than they did at faces that emitted mismatched calls . At the two oldest ages, infants looked at instances of matched and mismatched calls for about the same amount of time.

It’s already known that, after 3 months of age, babies associate people’s faces with their vocalizations, Lewkowicz notes. As perceptual experience in this vital social realm mounts during infancy, youngsters temporarily lose the broader capacity to recognize links between the facial movements and vocalizations of other species, he proposes.

Olivier Pascalis, a psychologist at the University of Sheffield in England, agrees. “There are clearly a series of transitions going on that move babies from a broad perceptual system toward a specialized one,” he says. Lewkowicz plans to examine at what age, after 10 months, sensory-matching ability reapp ears.




April 22, 2006 Vol. 169. (Pg. 246)


Constant of nature may have changed.

Scientists have long assumed that a few characteristics of the cosmos are as unvarying as the laws of physics themselves. These so-called constants of nature include the speed of light in a vacuum and the masses of some elementary particles.

Now, a team of physicists and astronomers in the Netherlands, Russia, and France has found signs that one of the constants has undergone a subtle shift since the infancy of the universe.

The new findings indicate that the ratio between the mass of the proton and that of the electron—a number known as mu—might have decreased by about two-thousandths of a percent in the past 12 billion years, say Elmar Reinhold, now of the European Space Agenc y in Noordwijk, the Netherlands, and his colleagues. The evidence for the change in the constant, which has a current value of 1,836.153, emerged from light-absorption patterns of hydrogen molecules, the scientists report in the April 21 Physical Review Letters.

If correct, it is a revolutionary result,” comments Victor V. Flambaum of the University of New South Wales in Sydney, Australia. “It doesn’t matter that the variation is small. If mu varies, we need new theoretical physics and cosmology.” Flambaum notes that variations in constants of nature as the cosmos evolves are part of some speculative theories of the universe, such as string theory, that call for dimensions beyond the familiar three of space plus one of time.

Since 2001, Flambaum and his colleagues have presented growing evidence that another constant, known as alpha or the fine-structure constant, has also varied. That variation, however, is less than the newly determined change in mu. Investigations by several other teams have found no evidence that alpha, which represents the strength of the electromagnetic force, has changed its value.

To arrive at the new findings for mu, Alexandre V. Ivanchik of the Ioffe Institute in St. Petersburg, Russia, and Patrick Petitjean of the Astrophysics Institute of Paris made extraordinarily precise telescope measurements of radiation coming from two quasars. The researchers focused on wavelengths absorbed by frigid clouds of hydrogen molecules in space. Because looking deep into space is equivalent to looking back in time, the quasar-radiation measurements probe characteristics of hydrogen molecules as they existed less than 2 billion years after the Big Bang.

Meanwhile, Reinhold and other members of the team, led by Wim Ubachs of the Free University of Amsterdam, determined with unprecedented accuracy the wave-lengths of light that hydrogen molecules absorb from laser beams in the laboratory today, 13.7 billion years after the Big Bang.

The scientists found the wavelengths to be slightly different in the two sets of data.Because the wavelengths that hydrogen molecules absorb depend on the value of mu, the results suggest that mu has changed.

Nonetheless, the absorption evidence gathered so far from two quasars isn’t strong enough to prove that mu varies, say members of the team and other scientists.

Investigators studying alpha have looked at 143 quasar systems, yet the notion that alpha has varied remains controversial, notes Michael T. Murphy of the University of Cambridge in England, one of the scientists who, with Flambaum, reported the alpha variation.

Scientists “need absolutely cast-iron proof” beyond the current study because the implications are so profound, agrees Lennox L. Cowie of the University of Hawaii, Manoa in Honolulu.




April 29, 2006. Vol. 169 (pg. 259

Space Engine

SOME SEEMINGLY QUIET BLACK HOLES ARE ACTUALLY EFFICIENT ENGINES that emit jets of high energy particles This finding, from the first study to directly measure the efficiency of black holes, offers a hint as to why the universe isn’t more crowded with stars.

All black holes swallow matter and spit out energy. Their gravitational pull traps clouds of hot, X-ray –emitting gas, and the black holes spew radiation or jets of high-energy particles.

The energy that black holes send out affects their environments. Scientists had presumed that young black holes producing quasars, which are beacons of light, are highly efficient. However, that efficiency hasn’t been directly measured because the quasars are too bright.

Instead of focusing on quasars, a team of scientists led by astrophysicist Steven W. Allen of Stanford University used NASA’s Chandra X-Ray Observatory to look at nine supermassive black holes, which are older than quasars and lie at the very centers of nearby giant elliptical galaxies. ‘These are the boring old black holes that we thought had stopped doing anything interesting a long time ago;’ says team member astrophysicist Christopher S. Reynolds of the University of Maryland at College Park. The team’s findings, announced this week, will be published in an upcoming Monthly Notices of the Royal Astronomical Society.

Though these black holes produce relatively little radiation, previous Chandra observations had noted the formation of large cavities in the surrounding gas clouds, as if the black holes were blowing bubbles tens of thousands of light-years across.

The team calculated the amount of energy needed to form those bubbles and then compared it with the growth of the gas disks that encircle the black holes. From those results, the scientists estimated that each black hole converts about 2.5 percent of the mass of captured gas into jets of particles. That’s about 25 times as efficient as nuclear power, Allen says.

“If you could make a car engine as efficient as a black hole engine, you could get about a billion miles out of 1 gallon of gas,” he says. ‘That’s green by anyone’s book.” The finding suggests that not just quasars but all black holes are efficient, whether they expel energy as radiation or jets of particles, Reynolds adds.

This research represents the “next big step” in understanding what black holes do and how galaxies and clusters evolve, says astrophysicist Kim Weaver of NASA’s God dard Space Flight Center in Greenbelt, Md., who was not on the study team.

The findings may hold clues to the puzzle of why galaxies aren’t as big a cosmologists’ models predict. Moving only slightly slower than the speed of light, the jets from black holes slam into the surrounding gas and heat it, preventing it from cooling enough to form stars, Weaver says.

These black holes “may be preventing galactic sprawl from taking over the neighborhood,” she adds.




April 29, 2006 Vol. 169 (pg. 261)

Science Human Structure

Throughly modern spine supported human ancestor.

BONES FROM A SPINAL COLUMN DISCOVERED AT A NEARLY 1.8-million-year-old site in central Asia support the controversial possibility that our ancient human ancestors spoke to one another.

Excavations in 2005 at Dmanisi, Georgia, yielded five (5) vertebrae from a Homo  ercctus individual, says anthropologist Marc R. Meyer of the University of Pennsylvania in Philadelphia. The finds occurred in previously dated sediment that has yielded several skulls now attributed to H. ereetus

The new discoveries represent the oldest known vertebrae for the genus Homo, Meyer announced last week at the annual meeting of the Paleoanthropology Society in San Juan, Puerto Rico. The fossils consist of one lumbar, two thoracic, and two cervical vertebrae.

Meyer and his colleagues—David Lordkipanidze and Abesalom Vekua, both of the Georgian State Museum in Tbilisi—compared the size, shape, and volume of the Dmanisi vertebrae with more than 2,200 corresponding bones from people, chimpanzees, and gorillas.

“The Dmanisi spinal column falls within the human range and would have comfortably accommodated a modern human spinal cord,” Meyer says.

Moreover, the fossil vertebrae would have provided ample structural support for the respiratory muscles needed to articulate words, he asserts. Although it’s impossible to confirm that our prehistoric ancestors talked, Meyer notes, H. erectus at Dmanisi faced no respiratory limitations on speech.

In contrast, the 1984 discovery in Kenya of a boy’s 1.6-million-year-old skeleton, identified by sonic researchers as H. erectus and by others as Horn t~gaster, yielded small, chimp-like vertebrae. Researchers initially suspected that the ancient youth and his presumably small-spined comrades lacked the respiratory control to talk as people do today.

In the past 5 years, investigators including Bruce Latimer of the Cleveland Museum of Natural History have suggested that the prehistoric boy offers a misleading view of H. erectus’ backbone. They contend that growth of the bony canal encasing his spinal cord had been stunted, and spinal cord compression would have impeded his movement and caused limb weakness.

Finding ancient, humanlike vertebrae at Dmanisi fits with Latimer’s view, Meyer says. Infant malnutrition, which often arrests growth of the human vertebral canal, may have affected the H. erectus youth, Meyer suggests.

The ancient boy, who died at age of 10 or so, would have required intensive pro-tection and provisioning, Meyer asserts. “Both altruism and spoken language may have been part of the behavioral repertoire of early Homo,” the Pennsylvania researcher says.

The modern-looking vertebrae at Dmanisi, remarks David Frayer of the University of Kansas in Lawrence, comport with earlier fossil-skull studies indicating that early Homo possessed a speech-ready vocal tract.

Robert C. McCarthy of Florida Atlantic University in Boca Raton disagrees. At the Paleoanthropology Society meeting, he presented vocal-tract reconstructions for various ancient Homo species suggesting that the capacity to articulate speech as well as people do now emerged exclusively in Horno sapiens around 50,000 years ago.

Before then, all members of the Homo genus—including H. sapiens —possessed a short set of neck vertebrae, resulting in a vocal tract with a restricted range of speech sounds, McCarthy and his coworkers argue.

Many populations today, including Australian aborigines, possess neck vertebrae comparable in length to those that McCarthy’s team considered inadequate for modem speech, Meyer responds.




May 6, 2006. Vol. 169. No. 18 (Pgs. 275-6)

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