- Ample Dark Matter Ignites Starburst Galaxies
- Physicists Build World’s First Antilaser
- Gallery: 10 Stunning Science Visualizations
- Heady Brew: Ice Age Mug Made From Skull
Posted: 17 Feb 2011 01:30 PM PST
By Liat Clark, Wired UK
Galaxies need 10 times less dark matter to sustain star formation than previously thought, but just the right amount can set off rapid star formation, a recent study suggests.
The discovery was made after European Space Agency photos showed evidence of dark matter 300 billion times the mass of our Sun supporting ancient galaxies. The galaxies — over 10 billion light years from Earth — are some of the most active in the universe, producing thousands of stars each year compared to the 10 a year the Milky Way produces on average.
"If you start with too little dark matter, then a developing galaxy would peter out," Asantha Cooray, the University of California astrophysicist who led the study, said in a press release. "If you have too much, then gas doesn't cool efficiently to form one large galaxy, and you end up with lots of smaller galaxies. But if you have the just the right amount of dark matter, then a galaxy bursting with stars will pop out."
The 300-billion-solar-mass size of ancient galaxies studied seems to encourage star formation more than any other previously recorded mass. It does not just sustain star formation, it facilitates and promotes it, changing previous theories of how galaxies are formed.
It is thought that dark matter, which is believed to make up around 20 percent of the universe's energy density, lays the groundwork for galaxy formation. Its gravitational pull attracts gas and dust, which gather and soon condense to form stars. The dark matter then collects around young galaxies in the form of giant spheres known as halos.
It does not reflect light and is therefore not visible to us. Cooray and his team detected it by measuring its gravitational pull on other, visible matter. Using the ESA's Herschel telescope they took infrared images at wavelengths 1,000 times longer than those visible to the naked eye. The photos can permeate dust-filled galaxies and Cooray used them to measure light emitted by the galaxies.
Their research concentrated on the Lockman Hole — an area of sky about the size of Earth's moon within the Ursa Major constellation. It is an ideal test area because there is minimal dust blocking the view.
The photos' web-like patterns are actually an intricate map of galaxies illuminated in infrared. They revealed that distant galaxies produce stars at a rate three to five times higher than young galaxies more easily visible to us. The images are far more detailed than those taken using the Hubble telescope, and by illuminating galaxies in this way much can be learned.
Jamie Bock, who studies Herschel's Spectral and Photometric Imaging Receiver at NASA's Jet Propulsion Laboratory in California, explained the photos are a huge advancement for galaxy formation studies.
"It turns out that it's much more effective to look at these patterns rather than the individual galaxies," he said in the release. "This is like looking at a picture in a magazine from a reading distance. … Herschel gives us the big picture of these distant galaxies, showing the influence of dark matter."
Galaxies may be sustained on even less dark matter, but they would be short-lived. Supernovas would be common in this instance, it is theorized, and without enough gravitational pull supplied by dark matter the remaining gases would dissipate.
Image: A computer simulation of dark matter distribution when the universe was about 3 billion years old. Blue shows the basic distribution of dark matter particles, red shows dark matter halos model, and yellow shows dark matter halos that are most likely to fuel starburst galaxies. (Alexandre Amblard/The Virgo Consortium/ESA)
Posted: 17 Feb 2011 12:00 PM PST
Less than a year after it was first suggested, the world's first antilaser is here. A team of physicists have built a contraption that, instead of flashing bright beams, utterly extinguishes specific wavelengths of light.
Conventional lasers create intense beams of light by stimulating atoms to spit out a coherent beam of light in which all the light waves march in lockstep. The crests of one wave match the crests of all the others, and troughs match up with troughs.
The antilaser does the reverse: Two perfect beams of laser light go in, and are completely absorbed.
"There will be nothing coming out again," said experimental physicist Hui Cao of Yale University, whose research group built the new device.
The device could find uses in fields from computing to medical imaging, the researchers report in the Feb. 18 issue of Science.
Yale physicist A. Douglas Stone, a co-author of the paper, first suggested the antilaser in a theoretical paper last July. Stone and colleagues had noticed that several other researchers had hinted at the idea of a laser that runs backward, and some problems in engineering called for a way to completely snuff out light. But no one had ever put the two ideas together.
"Others discovered independently that there's an optimal condition where they can have the best absorption," Cao said. "But they didn't realize this was a time-reversed laser. They didn't know they can get in principle perfect absorption."
To build the antilaser, which Cao and colleagues call a "coherent perfect absorber," the researchers split a beam from a titanium-sapphire laser in two. The laser emitted light in the infrared part of the electromagnetic spectrum, with longer wavelengths than the human eye can see.
Some of the light continued forward through the beam splitter, and the rest was forced into a sharp right turn. The physicists guided the light beams into a cavity containing a silicon wafer one micrometer thick. One beam entered from the left and one from the right. The distance each beam traveled determined the way the crests and troughs of the light waves aligned when they met in the wafer.
When the alignment was right, the light waves canceled each other out. The silicon absorbed the light and converted it to another form of energy, like heat or electrical current.
"It is a simple experiment," Cao said. "But it shows a very powerful way to control absorption."
The device can only absorb one wavelength of light at a time, but that wavelength can be adjusted by changing the thickness of the wafer.
Surprisingly, the antilaser switched from absorbent to reflective when the researchers changed the way the waves met in the wafer. Under certain conditions, the silicon crystal actually helped light escape.
"That is a little surprising," Cao said. "We can turn it on and off."
Theoretically, 99.999 percent of the light can be extinguished. Because of the physical limitations of the laser and the silicon wafer, the antilaser only absorbed 99.4 percent of the light.
That may be good enough, Cao said.
"For many applications, if you already have less than 1 percent coming out, you're already okay," she said. "I'm sure people in the community who have better lasers than us, I'm sure they will achieve much more impressive results. This is only the first demonstration of the principle."
The device may find uses in optical switches for future superfast computer boards that use light instead of electrons. It may also have medical applications, such as imaging a tumor through normally opaque human tissue.
The most exciting applications will no doubt be those no one has thought of yet. The laser itself was called "a solution without a problem" when it first showed up.
"It is quite novel and indeed surprising that in such a mature field one can come up with something fundamentally new," said physicist Marin Soljačić of MIT, who was not involved in the new work. "I think it opens a few exciting venues."
"Time-Reversed Lasing and Interferometric Control of Absorption." Wenjie Wan, Yidong Chong, Li Ge, Heeso Noh, A. Douglas Stone, Hui Cao. Science, Vol 331, Feb. 18, 2011. DOI: 10.1126/science.1200735.
Posted: 17 Feb 2011 11:01 AM PST
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All too often, the beauty of scientific knowledge gets trapped in monochrome graphs and jarring acronyms. The touch of talented artists, however, can set it free.
The 2010 International Science and Engineering Visualization Challenge released its top stunning entries today. They appear in the Feb. 18 issue of Science, which together with the National Science Foundation sponsored the event.
From GPS-tracked trash and nanoscale ripples to colliding quasars and hairy tomato seeds, dig into our favorite science visualizations in this gallery.
Human Immunodeficiency Virus
The HIV virus, a menacing genetic script that lethally infects more than 33 million people worldwide, looks more like a splotch under the planet's most powerful microscopes.
By scraping for details of the virus' structure from more than 100 studies in three different scientific fields, however, four focused artists summed it up into one intricate 3-D structure.
The model is now considered the most-detailed ever created for the contagion, and won the competition's first-place prize in illustrations.
Image: Ivan Konstantinov, Yury Stefanov, Aleksander Kovalevsky, Yegor Voronin/Visual Science Company [high-resolution version available]
Posted: 17 Feb 2011 05:00 AM PST
Ice Age folk who lived in what's now southwestern England gruesomely went from heads-off to bottoms-up. Bones excavated at a cave there include the oldest known examples of drinking cups or containers made out of human skulls, says a team led by paleontologist Silvia Bello of the Natural History Museum in London.
Measurements of a naturally occurring form of carbon in the skulls places them at about 14,700 years old, Bello and her colleagues report in a paper published online Feb. 16 in PLoS ONE. Prehistoric cave denizens cleaned the skulls before using stone tools to shape the upper parts of the brain cases into containers, the researchers say.
Bello suspects that ice age Britons hoisted hollowed-out craniums in rituals of some kind. Other human bones found near the skull cups show signs of flesh and marrow removal, a result either of cannibalism or mortuary practice. The striking similarities between the cave finds and historical examples of drinking cups made out of skulls further support a ritual role for the ice age receptacles, Bello says.
Two French sites previously yielded skull containers presumed to date to between 15,000 and 12,000 years ago, but those finds have not been directly dated.
Image: Natural History Museum
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