[http://www.sciencenews.org/view/generic/id/43531/title/Using_dead_stars_to_spot_gravitational_waves]
New technique could tune into cosmic symphony on the cheap
By Ron Cowen

 

WARPED TRAVELS
Gravitational waves warp spacetime near rapidly rotating, radio-wave emitting stars called millisecond pulsars (shown as six points at the perimeter). Such disruptions alter the arrival time of the radio waves at Earth (center).







DENVER — A bunch of dead stars could serve as ready-made recorders for gravitational waves — subtle ripples in spacetime that if discovered would be the crowning achievement of Einstein’s theory of general relativity, astronomers propose. Researchers have been spending billions of dollars to perfect sensitive, kilometer-long devices on the ground and launch even more sophisticated experiments in space to detect this cosmic symphony.

The new search technique would instead rely on radio waves generated like clockwork by millisecond pulsars — the collapsed remnants of massive stars that spin about once every one to 10 milliseconds. The speed at which these pulsars rotate enables researchers to measure the timing of the waves’ arrival at Earth with high accuracy.

Measuring arrival time is critical, says Frederick Jenet of the University of Texas at Brownsville and Texas Southmost College, who presented his team’s proposal on May 3 at the American Physical Society meeting. Colleague Andrea Lommen of Franklin & Marshall College in Lancaster, Pa., reported additional details on May 5.

A gravitational wave passing by the pulsar would warp spacetime, altering the arrival time of the radio waves at Earth ever so slightly. First the pulses would appear to a little earlier, then a little later. The changes in arrival time would depend predictably on the phase and direction of propagation of the gravitational wave, as well as its distance from the pulsar, Jenet notes.

To detect a general background of gravitational waves, astronomers would need to monitor 20 millisecond pulsars for five to 10 years, with the arrival time of the radio waves determined to an accuracy of 100 nanoseconds, Jenet estimates. Recording gravitational waves from a pair of merging supermassive black holes would require five pulsars with radio wave arrival times known to an even higher accuracy, 10 nanoseconds, he adds.

“We currently have about 20 millisecond pulsars, but only five of these can be timed to the needed precision,” he notes. Astronomers need to find more millisecond pulsars in order to conduct the proposed search.

The pulsar technique, Jenet says, is best suited for recording long-period gravitational waves — those with a period of months to years — because those waves would induce the largest fluctuations in the arrival time of the radio waves. Intriguingly, long-period gravitational waves are preferentially generated by pairs of the most massive black holes — the giant beasts that lie at the center of galaxies.

The idea of using pulsars to search for gravitational waves dates back to the late 1970s, Jenet says, but only recently have dedicated searches begun worldwide. “Personally, the romantic notion of building a galactic-scale gravitational wave observatory using exotic stars as part of the instrument itself seems quite appealing,” he says.

Using pulsars to search for gravitational waves “is not a crazy idea but a well-established area of research,” says Tom Prince of Caltech. Both the increased sensitivity of radio telescopes and the discovery of additional millisecond pulsars have taken the idea from intriguing to practical.

Prince leads an effort to launch a gravitational wave detector called LISA into space sometime in the next decade. LISA uses a trio of spacecraft, each housing a freely floating test mass, to record the passage of a gravitational wave. LISA will detect high-frequency gravitational waves produced by stellar-size black holes and neutron stars, which the pulsar method can’t. But the pulsar method is available now, without the need for new telescopes, Jenet says.

Scientists are currently using several large-scale gravitational-wave detectors on Earth, including the twin LIGO detectors, one located near Livingston, La., and the other in Hanford, Wash.

[http://www.sciencenews.org/view/generic/id/43519/title/Hobbit_foot%2C_hippo_skulls__deepen_ancestral_mystery]

Fossil studies add some new twists to debate about a tiny, humanlike species
By Bruce Bower 

 
WALKING SMALL
Bones from the left foot of a partial hobbit skeleton (top) indicate that this individual could walk upright but still possessed many primitive foot features. This analysis raises questions about the evolutionary origins of the tiny Indonesian species. A lower-right leg bone from the same specimen is also shown.


Fossil hobbits followed a simple motto: Walk, don’t run. That’s the implication of a new analysis of foot bones from an 18,000-year-old partial skeleton assigned to the controversial species Homo floresiensis, or hobbits.

But the relatively long and unusually primitive left foot of the female skeleton, known as LB1, feeds into growing confusion about the evolutionary origins of hobbits, researchers report in the May 7 Nature. So does another new investigation, of fossil hippo skulls, in the same issue.

“The hobbit foot could have made something like the more than 3-million-year-old Laetoli footprints in Tanzania but probably not the modern-looking footprints ascribed to 1.5-million-year-old H. erectus in Kenya,” says anthropologist William Jungers of Stony Brook University Medical Center in New York (SN: 3/28/09, p. 14). Hobbits walked with a shuffling gait but would have had difficulty running, Jungers and his colleagues report.

LB1 stood at least a meter tall and displays primitive-looking skeletal traits from head to toe, Jungers says. H. floresiensis must have evolved from a species that was older, smaller and anatomically more primitive than Asian H. erectus, perhaps 2.4-million-year-old Homo habilis in Africa, Jungers proposes. An evolutionary transition from H. habilis to hobbits would have required little or no reduction in body size, in his view.

This proposal clashes with earlier interpretations of other hobbit fossils, also from the Indonesian island of Flores, that suggest a large-bodied H. erectus population from southeastern Asia evolved into H. floresiensis. H. erectus lived in southeastern Asia by 90,000 years ago, when hobbits first inhabited Flores. And other animals are known to have evolved into small species on islands, a process known as island dwarfing.

H. erectus could indeed have evolved a brain as small as that of LB1 via island dwarfing, assert Eleanor Weston and Adrian Lister, both paleontologists at the Natural History Museum in London. In support of that scenario, they report that two extinct dwarf species of hippopotamus from Madagascar possessed surprisingly small brains, based on a comparison with the modern-day hippo that evolved from the dwarf animals.

Weston and Lister studied fossil skulls of 36 pygmy hippos from species that died out about 6,000 years ago. Relative brain sizes of these creatures were as much as 30 percent smaller than would be expected by simply scaling down their larger evolutionary relatives.

These results, along with evidence of substantial brain-size reductions in island-dwarfed foxes (SN: 5/10/08, p. 7), suggest that H. erectus or another large-bodied ancestor could have evolved into hobbits, comments anthropologist Dean Falk of Florida State University in Tallahassee. That ancestral species contributed humanlike brain traits to H. floresiensis (SN: 4/25/09, p.9), Falk hypothesizes.

But island dwarfing in hobbits could not have produced so many primitive skeletal traits, Jungers responds. Consider that, relative to leg length, LB1’s foot is proportionally as long as that of Lucy, a 3.2-million-year-old species in the human evolutionary family. Other primitive foot features of LB1 include long, curved toes; a stubby, chimplike big toe; and no arch.

Scientists who regard LB1 as a modern human who suffered from a brain-stunting developmental disorder, and not a separate species, remain unconvinced. LB1’s foot looks long in Junger’s analysis only because the foot is being compared with an extremely short upper-leg bone, says evolutionary biologist Robert Eckhardt of Pennsylvania State University in University Park. An upper leg of that size — as well as many asymmetrically shaped head and lower-body bones — could have resulted from a developmental abnormality of some kind, Eckardt suggests.

Earlier comparisons of brain-size relationships in many mammal species, including island-living primates, indicated that LB1’s brain is too small to be that of an 18,000-year-old hominid, adds anthropologist Robert Martin of The Field Museum in Chicago. No data exist on relative brain size for a common ancestor of dwarf hippos and their mainland progeny, leaving Weston and Lister without a key comparison group, Martin notes.

The possibility that LB1’s many primitive skeletal features resulted from a developmental disorder “has not been seriously examined,” he says.

[http://www.sciencenews.org/view/generic/id/43434/title/Ants_may_be_the_Undead]

Living Argentine ant workers carry both a "dead" signal and an override "not dead yet" signal
By Susan Milius
Web edition : Monday, May 4th, 2009


UNDERTAKER
Ant nests have great undertaker capacity. Workers detect the dead and haul them outside to a pile of debris and corpses, often within an hour after death. Here a worker carries a young ant in the pupal stage to the refuse pile.Photo courtsey of the National Academy of Sciences and PNAS

Colonies of Argentine ants spreading around the world might be real-life invasions of the living dead.

Normal, still-breathing adult workers carry chemicals signaling “Dead ant — haul to burial pile” on their outer covering, proposes Dong-Hwan Choe of the University of California, Riverside.

What prevents awkward mistakes about who’s really dead are two additional compounds also found on the covering of living ants, Choe suggests. These compounds temporarily inhibit responses to the death cues by signaling, “Wait — still alive so far,” Choe and his colleagues report online May 4 in Proceedings of the National Academy of Sciences.

Tests of ant reactions to chemicals applied to ant pupae provide the first experimental evidence for this “not-dead-yet” signaling system, Choe says.

Undertaker cues in ants have fascinated biologists studying the evolution of social living. “Being able to quickly remove dead individuals and other possible sources of pathogens and contaminants is extremely important for all animals living in societies, including us,” says Patrizia d’Ettorre of the University of Copenhagen. “Think about all the effort and money that we invest daily in waste management.”

Understanding life or death cues might also help in devising new ways to control Argentine ants, Choe says. The small ants have been moving into new territories worldwide and disrupting native ecosystems. He’s investigating ways to spread ant-killer from the dead ants to the colony mates that haul them away.

Earlier experiments had searched for a death cue that appeared on a corpse after death. Anesthetized ants typically get left alone until they come around, so stillness alone doesn’t trigger the undertakers. Yet a worker that really does die inside the nest gets hauled outside to a pile of mixed rubbish. But researchers haven’t yet agreed on what chemicals are involved and how they work.

Choe and his colleagues dropped fresh and not-so-fresh ant corpses into a lab colony and found that ants that had been dead for only an hour triggered about the same strong urge to remove them as ants that had been dead for 24 hours. Such a speedy response seems awfully fast for decomposition chemistry to trigger disposal, Choe says. So he and his colleagues experimented with the notion that, instead, some “still alive” cue fades fast.

To test different chemical signals, the researchers took advantage of the ants’ natural tendency to retrieve young ants at the pupal stage that somehow end up outside the nest. Pupae don’t have the same surface chemistry as adults, so researchers doused them with various signaling brews.

When treated with chemical extracts of ants that had been dead for an hour, 18 of 20 pupae were hauled to the refuse pile as if they were dead adults, suggesting that chemicals did play a role in the removal.

The team also treated the pupae with two compounds found on living ants and freshly dead ants but not found on ants dead an hour or more. These two compounds, dolichodial and iridomyrmecin, naturally dissipate quickly, the team found.

When doused with these compounds, the pupae were ignored. They were neither disposed of nor promptly brought back to the nest, suggesting other adults treated them as if they were indeed living adult workers, Choe and his colleagues say. Eventually, the workers did retrieve the pupae, as would be expected when an override signal — the dolichodial and iridomyrmecin — faded away, the researchers report.

Walter Tschinkel of Florida State University in Tallahassee says the idea is plausible but hasn’t been proven. “They did not put the last nail in that coffin,” Tschinkel says. Using pupae didn’t seem an appropriate test to him. He says he’d like to see what happens to dead adult ants treated with those compounds.

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