Tuesday, October 6, 2009

ODDBALL STARS EXPLAINED

0 comentarios

New observations solve longstanding mystery of tipped rotation. In addition to shedding light on how binary stars form, the explanation knocks down a possible challenge to Einstein's theory of relativity.

A pair of unusual stars known as DI Herculis has confounded astronomers for three decades, but new observations by MIT researchers and their colleagues have provided data that they say solve the mystery once and for all.

It has long been clear that there was something odd going on in this double-star system, but it wasn't clear just what that was. The precession of the orbits of the two stars around each other — that is, the way the plane of those orbits change their tilt over time, like the wobbling of a top as it winds down — seems to take place four times more slowly than established theory says it should. The anomaly is so unexpected that at one point it was seen as possible evidence against Einstein's long-accepted theory of relativity.

But the true explanation seems to be much less radical, though still unique among observed stars. Both of them, it turns out, are rotating tipped over on their sides, relative to the plane of their orbits around each other, instead of straight upright like most binary stars. Because stars rotate fast enough to have significant equatorial bulges (just like on Earth, which is wider at the equator than pole-to-pole), these tipped-over bulges produce an unusual tidal interaction between them that counteracts the forces that would normally cause the expected rate of precession, and that accounts for the observed slowing of this effect. And so, relativity has dodged another bullet.

"It's been a riddle for 30 years," says MIT postdoctoral researcher Simon Albrecht, co-author of a new paper appearing in the Sept. 17 issue of Nature that describes the solution. New observations of the stars, which are about 2,000 light years from Earth but orbit each other with a separation of only about one-fifth the distance from the Earth to the sun, were carried out by Albrecht, assistant professor of physics Joshua Winn, and others. Using a high-resolution spectrograph called Sophie on a 1.93-meter telescope at the Observatoire de Haute-Provence in France, they found an answer to the mystery.

The new observations, after detailed analysis, reveal that one of the two stars is tipped over by at least 70 degrees from the vertical, and the other is tipped the opposite way by more than 80 degrees.

One lesson of this finding, says Winn, is to "check your assumptions." The more astronomers learn about the details of stars and planetary systems, the more odd variations keep turning up. "Everyone always assumed that planets orbit in the same plane as their star's rotation," until some recent discoveries of exceptions to that rule, "and that binary stars are aligned. These assumptions are just not true."

The assumption has been that binary stars should always have their spin axes aligned, because they are believed to have formed from a single swirling cloud of dust and gas, whose direction of rotation should be inherited by the resulting stars. Now that this drastically misaligned pair of stars has been found, theorists might be forced to rethink how such binary systems form. "Maybe most binary stars are formed misaligned," but then most of them become aligned as a result of their gravitational interaction, Winn says. Or maybe it's the opposite: most form aligned and some become tidally disturbed and lose their alignment.

Other star and planet systems are "certainly more dynamic than we would have guessed, based on our solar system orbits," Albrecht says.

It's also possible that these two stars formed separately and one was captured by the gravitational attraction of the other after a close encounter, but Albrecht says that is unlikely, because the stars are near-twins. "These are so similar in mass and lifetime that we wouldn't expect that," he says.

(Photo: Simon Albrecht)

Massachusetts Institute of Technology

GETTING A LEG UP ON WHALE AND DOLPHIN EVOLUTION

0 comentarios

When the ancestors of living cetaceans—whales, dolphins and porpoises—first dipped their toes into water, a series of evolutionary changes were sparked that ultimately nestled these swimming mammals into the larger hoofed animal group. But what happened first, a change from a plant-based diet to a carnivorous diet, or the loss of their ability to walk? A new paper published in PLoS One resolves this debate using a massive data set of the morphology, behavior, and genetics of living and fossil relatives. Cetacean ancestors probably moved into water before changing their diet (and their teeth) to include carnivory; Indohyus, a 48-million year-old semi-aquatic herbivore, and hippos fall closest to cetaceans when the evolutionary relationships of the larger group are reconstructed.

"If you only had living taxa to figure out relationships within this group of animals, you would miss a large amount of diversity and part of the picture of what is going on," says Michelle Spaulding, lead author of the study and a graduate student affiliated with the American Museum of Natural History. "Indohyus is interesting because this fossil combines an herbivore's dentition with adaptations such as ear bones that are adapted for hearing under water and are traditionally associated with whales only."
The origin of whales, dolphins, and porpoises—with their highly modified legs and lack of hair—has long been a quandary for mammalogists. About 60 years ago, researchers first suggested that cetaceans were related to plant-eating ungulates, specifically to even-toed, artiodactyl mammals like sheep, antelope and pigs. In other words, carnivorous killer whales and fish-eating dolphins were argued to fit close to the herbivorous hoofed animal group. More recent genetic research found that among artiodactyls, hippos are the cetaceans' closest living relatives.

Because no one would ever link hippos and whales based on their appearance, fossil evidence became an important way to determine the precise evolutionary steps that cetacean ancestors took. Traditionally, the origin of whales was linked to the mesonychids, an extinct group of carnivores that had singly-hoofed toes. The recent discovery of Indohyus, a clearly water-adapted herbivore, complicates this picture (as new fossils often do) because of ear bones similar to those of modern cetaceans, which are theorized to help the animal have heard better while under the water.

To tease apart different potential evolutionary histories (whether carnivory or water adaptations occurred first; the mesonychid or Indohyus relatedness ideas), Spaulding and colleagues mapped the evolutionary relationships among more than 80 living and fossil taxa (in other words, species and/or genera). These taxa were scored for 661 morphological and behavioral characters (such as presence of hair or the shape of and ankle bone). Forty-nine new DNA sequences from five nuclear genes were also added to the mix of more than 47,000 characters; both morphological and genetic data build on previous analyses by authors Maureen O'Leary of Stony Brook University and John Gatesy of University of California at Riverside. In addition, Indohyus, carnivores (dogs and cats), and an archaic group of meat-eating mammals called creodonts were included.

The team found that the least complex evolutionary tree places Indohyus and similar fossils close to whales, while mesonychids are more distantly related. Hippos remain the closest living relatives. These results suggest that cetacean ancestors transitioned to water before becoming carnivorous but that the meat-eating diet developed while these ancestors could still walk on land.

"How do you put flesh and movement onto a fossil?" asks author O'Leary. "The earliest stem whale probably ate prey in water while still being able to walk on land. Indohyus has some adaptations for hearing under water but also ate plants, while Ambulocetus (a walking whale that lived about 50 million years ago) seems to have been carnivorous."

"There is deep conflict in the evolutionary tree," says Spaulding. "The backbone of the tree is robust and stable, but you have these fairly large clades that move around relative to this backbone(Indohyus and mesonychids) We need to really re-examine characters carefully and see what suite of traits are the truly derived in different taxa to fully resolve this tree."

(Photo: Carl Buell)

American Museum of Natural History

TWIN KECK TELESCOPES PROBE DUAL DUST DISKS

0 comentarios

Astronomers using the twin 10-meter telescopes at the W. M. Keck Observatory in Hawaii have explored one of the most compact dust disks ever resolved around another star. If placed in our own solar system, the disk would span about four times Earth’s distance from the sun, reaching nearly to Jupiter’s orbit. The compact inner disk is accompanied by an outer disk that extends hundreds of times farther.

The centerpiece of the study is the Keck Interferometer Nuller (KIN), a device that combines light captured by both of the giant telescopes in a way that allows researchers to study faint objects otherwise lost in a star’s brilliant glare. "This is the first compact disk detected by the KIN, and a demonstration of its ability to detect dust clouds a hundred times smaller than a conventional telescope can see," said Christopher Stark, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Md., who led the research team.

By merging the beams from both telescopes in a particular way, the KIN essentially creates a precise blind spot that blocks unwanted starlight but allows faint adjacent signals – such as the light from dusty disks surrounding the star – to pass through.

In April 2007, the team targeted 51 Ophiuchi, a young, hot, B-type star about 410 light-years away in the constellation Ophiuchus. Astronomers suspect the star and its disks represent a rare, nearby example of a young planetary system just entering the last phase of planet formation, although it is not yet known whether planets have formed there.

"Our new observations suggest 51 Ophiuchi is a beautiful protoplanetary system with a cloud of dust from comets and asteroids extremely close to its parent star," said Marc Kuchner, an astronomer at Goddard and a member of the research team.

Planetary systems are surprisingly dusty places. Much of the dust in our solar system forms inward of Jupiter's orbit, as comets crumble near the sun and asteroids of all sizes collide. This dust reflects sunlight and sometimes can be seen as a wedge-shaped sky glow – called the zodiacal light – before sunrise or after sunset.

Dusty disks around other stars that arise through the same processes are called "exozodiacal" clouds. "Our study shows that 51 Ophiuchi’s disk is more than 100,000 times denser than the zodiacal dust in the solar system," explained Stark." This suggests that the system is still relatively young, with many colliding bodies producing vast amounts of dust."

To decipher the structure and make-up of the star’s dust clouds, the team combined KIN observations at multiple wavelengths with previous studies from NASA’s Spitzer Space Telescope and the European Southern Observatory’s Very Large Telescope Interferometer in Chile.

The inner disk extends about 4 Astronomical Units (AU) from the star and rapidly tapers off. (One AU is Earth’s average distance from the sun, or 93 million miles.) The disk’s infrared color indicates that it mainly harbors particles with sizes of 10 micrometers – smaller than a grain of fine sand – and larger.

The outer disk begins roughly where the inner disk ends and reaches about 1,200 AU. Its infrared signature shows that it mainly holds grains just one percent the size of those in the inner disk – similar in size to the particles in smoke. Another difference: The outer disk appears more puffed up, extending farther away from its orbital plane than the inner disk.

"We suspect that the inner disk gives rise to the outer disk," explained Kuchner. As asteroid and comet collisions produce dust, the larger particles naturally spiral toward the star. But pressure from the star’s light pushes smaller particles out of the system. This process, which occurs in our own solar system, likely operates even better around 51 Ophiuchi, a star 260 times more luminous than the sun.

(Photo: NASA/JPL-Caltech/T. Pyle (SSC))

NASA

UW LAB DEMONSTRATES 3-D PRINTING IN GLASS

0 comentarios

A team of engineers and artists working at the University of Washington's Solheim Rapid Manufacturing Laboratory has developed a way to create glass objects using a conventional 3-D printer. The technique allows a new type of material to be used in such devices.

The team's method, which it named the Vitraglyphic process, is a follow-up to the Solheim Lab's success last spring printing with ceramics.

"It became clear that if we could get a material into powder form at about 20 microns we could print just about anything," said Mark Ganter, a UW professor of mechanical engineering and co-director of the Solheim Lab. (Twenty microns is less than one thousandth of an inch.)

Three-dimensional printers are used as a cheap, fast way to build prototype parts. In a typical powder-based 3-D printing system, a thin layer of powder is spread over a platform and software directs an inkjet printer to deposit droplets of binder solution only where needed. The binder reacts with the powder to bind the particles together and create a 3-D object.

Glass powder doesn't readily absorb liquid, however, so the approach used with ceramic printing had to be radically altered.

"Using our normal process to print objects produced gelatin-like parts when we used glass powders," said mechanical engineering graduate student Grant Marchelli, who led the experimentation. "We had to reformulate our approach for both powder and binder."

By adjusting the ratio of powder to liquid the team found a way to build solid parts out of powdered glass purchased from Spectrum Glass in Woodinville, Wash. Their successful formulation held together and fused when heated to the required temperature.

Glass is a material that can be transparent or opaque, but is distinguished as an inorganic material (one which contains no carbon) that solidifies from a molten state without the molecules forming an ordered crystalline structure. Glass molecules remain in a disordered state, so glass is technically a super-cooled liquid rather than a true solid.

In an instance of new technology rediscovering and building on the past, Ganter points out that 3-D printed glass bears remarkable similarities to pate de verre, a technique for creating glassware. In pate de verre, glass powder is mixed with a binding material such as egg white or enamel, placed in a mold and fired. The technique dates from early Egyptian times. With 3-D printing the technique takes on a modern twist.

As with its ceramics 3-D printing recipe, the Solheim lab is releasing its method of printing glass for general use.

"By publishing these recipes without proprietary claims, we hope to encourage further experimentation and innovation within artistic and design communities," said Duane Storti, a UW associate professor of mechanical engineering and co-director of the Solheim Lab.

Artist Meghan Trainor, a graduate student in the UW's Center for Digital Arts and Experimental Media working at the Solheim Lab, was the first to use the new method to produce objects other than test shapes.

"Creating kiln-fired glass objects from digital models gives my ideas an immediate material permanence, which is a key factor in my explorations of digital art forms," Trainor said. "Moving from idea to design to printed part in such a short period of time creates an engaging iterative process where the glass objects form part of a tactile feedback loop."

Ronald Rael, an assistant professor of architecture at the University of California, Berkeley, has been working with the Solheim Lab to set up his own 3-D printer. Rael is working on new kinds of ceramic bricks that can be used for evaporative cooling systems.

"3-D printing in glass has huge potential for changing the thinking about applications of glass in architecture," Rael said. "Before now, there was no good method of rapid prototyping in glass, so testing designs is an expensive, time-consuming process." Rael adds that 3-D printing allows one to insert different forms of glass to change the performance of the material at specific positions as required by the design.

The new method would also create a way to repurpose used glass for new functions, Ganter said. He sees recycled glass as a low-cost material that can help bring 3-D printing within the budget of a broader community of artists and designers.

(Photo: University of Washington)

University of Washington

ROUGH DAY AT WORK? YOU WON'T FEEL LIKE EXERCISING

0 comentarios
A new study, published in Psychology and Health, reveals that if you use your willpower to do one task, it depletes you of the willpower to do an entirely different task.

"Cognitive tasks, as well as emotional tasks such as regulating your emotions, can deplete your self-regulatory capacity to exercise," says Kathleen Martin Ginis, associate professor of kinesiology at McMaster University, and lead author of the study.

Martin Ginis and her colleague Steven Bray used a Stroop test to deplete the self-regulatory capacity of volunteers in the study. (A Stroop test consists of words associated with colours but printed in a different colour. For example, "red" is printed in blue ink.) Subjects were asked to say the colour on the screen, trying to resist the temptation to blurt out the printed word instead of the colour itself.

"After we used this cognitive task to deplete participants' self-regulatory capacity, they didn't exercise as hard as participants who had not performed the task. The more people "dogged it" after the cognitive task, the more likely they were to skip their exercise sessions over the next 8 weeks. "You only have so much willpower."

Still, she doesn't see that as an excuse to let people loaf on the sofa.

"There are strategies to help people rejuvenate after their self-regulation is depleted," she says. "Listening to music can help; and we also found that if you make specific plans to exercise—in other words, making a commitment to go for a walk at 7 p.m. every evening—then that had a high rate of success."

She says that by constantly challenging yourself to resist a piece of chocolate cake, or to force yourself to study an extra half-hour each night, then you can actually increase your self-regulatory capacity.

"Willpower is like a muscle: it needs to be challenged to build itself," she says.

The study was made possible through funding by the Social Sciences and Humanities Research Council of Canada.

McMaster University

SCANDINAVIANS ARE DESCENDED FROM STONE AGE IMMIGRANTS

0 comentarios
Today's Scandinavians are not descended from the people who came to Scandinavia at the conclusion of the last ice age but, apparently, from a population that arrived later, concurrently with the introduction of agriculture. This is one conclusion of a new study straddling the borderline between genetics and archaeology, which involved Swedish researchers and which has now been published in the journal Current Biology.

"The hunter-gatherers who inhabited Scandinavia more than 4,000 years ago had a different gene pool than ours," explains Anders Götherström of the Department of Evolutionary Biology at Uppsala University, who headed the project together with Eske Willerslev of the Centre for GeoGenetics at the University of Copenhagen.

The study, a collaboration among research groups in Sweden, Denmark and the UK, involved using DNA from Stone Age remains to investigate whether the practices of cultivating crops and keeping livestock were spread by immigrants or represented innovations on the part of hunter-gatherers.

"Obtaining reliable results from DNA from such ancient human remains involves very complicated work," says Helena Malmström of the Department of Evolutionary Biology at Uppsala University.

She carried out the initial DNA sequencings of Stone Age material three years ago. Significant time was then required for researchers to confirm that the material really was thousands of years old.

"This is a classic issue within archaeology," says Petra Molnar at the Osteoarchaeological Research Laboratory at Stockholm University. "Our findings show that today's Scandinavians are not the direct descendants of the hunter-gatherers who lived in the region during the Stone Age. This entails the conclusion that some form of migration to Scandinavia took place, probably at the onset of the agricultural Stone Age. The extent of this migration is as of yet impossible to determine."

Uppsala University

Followers

Archive

 

Selected Science News. Copyright 2008 All Rights Reserved Revolution Two Church theme by Brian Gardner Converted into Blogger Template by Bloganol dot com