Monday, December 20, 2010


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Arizona State University's Judd Bowman and Alan Rogers of Massachusetts Institute of Technology have developed a small-scale radio astronomy experiment designed to detect a never-before-seen signal from the early universe during this period of time, a development that has the potential to revolutionize the understanding of how the first galaxies formed and evolved.

"Our goal is to detect a signal from the time of the Epoch of Reionization. We want to pin down when the first galaxies formed and then understand what types of stars existed in them and how they affected their environments," says Bowman, an assistant professor at the School of Earth and Space Exploration in ASU's College of Liberal Arts and Sciences.

Bowman and Rogers deployed a custom-built radio spectrometer called EDGES to the Murchison Radio-astronomy Observatory in Western Australia to measure the radio spectrum between 100 and 200 MHz. Though simple in design – consisting of just an antenna, an amplifier, some calibration circuits, and a computer, all connected to a solar-powered energy source – its task is highly complex. Instead of looking for early galaxies themselves, the experiment looks for the hydrogen gas that existed between the galaxies. Though an extremely difficult observation to make, it isn't impossible, as Bowman and Rogers have demonstrated in their paper published in Nature on Dec. 9.

"This gas would have emitted a radio line at a wavelength of 21 cm – stretched to about 2 meters by the time we see it today, which is about the size of a person," explains Bowman. "As galaxies formed, they would have ionized the primordial hydrogen around them and caused the radio line to disappear. Therefore, by constraining when the line was present or not present, we can learn indirectly about the first galaxies and how they evolved in the early universe." Because the amount of stretching, or redshifting, of the 21 cm line increases for earlier times in the Universe's history, the disappearance of the inter-galactic hydrogen gas should produce a step-like feature in the radio spectrum that Bowman and Rogers measured with their experiment.

Radio measurements of the redshifted 21 cm line are anticipated to be an extremely powerful probe of the reionization history, but they are very challenging. The experiment ran for three months, a rather lengthy observation time, but a necessity given the faintness of the signal compared to the other sources of emission from the sky.

"We carefully designed and built this simple instrument and took it out to observe the radio spectrum and we saw all kinds of astronomical emission but it was 10,000 times stronger than the theoretical expectation for the signal we are looking for," explains Bowman. "That didn't surprise us because we knew that going into it, but it means it's very hard to see the signal we want to see."

The low frequency radio sky is dominated by intense emission from our own galaxy that is many times brighter than the cosmological signal. Add to that the interference from television, FM radio, low earth orbit satellites, and other telecommunications radio transmitters (present even in remote areas like Australia's Outback) and it is a real challenge. Filtering out or subtracting these troublesome foreground signals is a principal focus of instrument design and data analysis techniques. Fortunately, many of the strongest foregrounds have spectral properties that make them possible to separate from the expected EoR signals.

After careful analysis of their observations, Bowman and Rogers were able to show that the gas between galaxies could not have been ionized extremely rapidly. This marks the first time that radio observations have directly probed the properties of primordial gas during the EoR and paves the way for future studies. "We're breaking down barriers to open an entirely new window into the early universe," Bowman says.

The next generation of large radio telescopes is under construction right now to attempt much more sophisticated measurements of the 21 cm line from the EoR. Bowman is the project scientist for one of the telescopes called the Murchison Widefield Array. According to him, the most likely physical picture for the EoR looked like a lot of bubbles that started percolating out from galaxies and then grew together – but that idea needs to be tested. If lots of galaxies all put out a little bit of radiation, then there would be many little bubbles everywhere and those would grow and eventually merge like a really fizzy and frothy foam. On the other hand, if there were just a few big galaxies that each emitted a lot of radiation then there would have been only a few big bubbles that grew together.

"Our goal, eventually, is to make radio maps of the sky showing how and when reionization occurred. Since we can't make those maps yet, we are starting with these simple experiments to begin to constrain the basic properties of the gas and how long it took for galaxies to change it," explains Bowman. "This will improve our understanding of the large-scale evolution of the universe."

(Photo: Judd Bowman)

Arizona State University


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Zen meditation has many health benefits, including a reduced sensitivity to pain. According to new research from the Université de Montréal, meditators do feel pain but they simply don't dwell on it as much. These findings, published in the month's issue of Pain, may have implications for chronic pain sufferers, such as those with arthritis, back pain or cancer.

“Our previous research found that Zen meditators have lower pain sensitivity. The aim of the current study was to determine how they are achieving this,” says senior author Pierre Rainville, researcher at the Université de Montréal and the Institut universitaire de gériatrie de Montréal. “Using functional magnetic resonance imaging, we demonstrated that although the meditators were aware of the pain, this sensation wasn't processed in the part of their brains responsible for appraisal, reasoning or memory formation. We think that they feel the sensations, but cut the process short, refraining from interpretation or labelling of the stimuli as painful.”

Rainville and his colleagues compared the response of 13 Zen meditators to 13 non-meditators to a painful heat stimulus. Pain perception was measured and compared with functional MRI data. The most experienced Zen practitioners showed lower pain responses and decreased activity in the brain areas responsible for cognition, emotion and memory (the prefrontal cortex, amygdala and hippocampus). In addition, there was a decrease in the communication between a part of the brain that senses the pain and the prefrontal cortex.

“Our findings lead to new insights into mind/brain function,” says first author, Joshua Grant, a doctoral student at the Université de Montréal. “These results challenge current concepts of mental control, which is thought to be achieved by increasing cognitive activity or effort. Instead, we suggest it is possible to self-regulate in a more passive manner, by ‘turning off' certain areas of the brain, which in this case are normally involved in processing pain.”

“The results suggest that Zen meditators may have a training-related ability to disengage some higher-order brain processes, while still experiencing the stimulus,” says Rainville. “Such an ability could have widespread and profound implications for pain and emotion regulation and cognitive control. This behaviour is consistent with the mindset of Zen and with the notion of mindfulness.”

(Photo: IStock)

Université de Montréal


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A once fertile landmass now submerged beneath the Persian Gulf may have been home to some of the earliest human populations outside Africa, according to an article published today in Current Anthropology.

Jeffrey Rose, an archaeologist and researcher with the University of Birmingham in the U.K., says that the area in and around this "Persian Gulf Oasis" may have been host to humans for over 100,000 years before it was swallowed up by the Indian Ocean around 8,000 years ago. Rose's hypothesis introduces a "new and substantial cast of characters" to the human history of the Near East, and suggests that humans may have established permanent settlements in the region thousands of years before current migration models suppose.

In recent years, archaeologists have turned up evidence of a wave of human settlements along the shores of the Gulf dating to about 7,500 years ago. "Where before there had been but a handful of scattered hunting camps, suddenly, over 60 new archaeological sites appear virtually overnight," Rose said. "These settlements boast well-built, permanent stone houses, long-distance trade networks, elaborately decorated pottery, domesticated animals, and even evidence for one of the oldest boats in the world."

But how could such highly developed settlements pop up so quickly, with no precursor populations to be found in the archaeological record? Rose believes that evidence of those preceding populations is missing because it's under the Gulf.

"Perhaps it is no coincidence that the founding of such remarkably well developed communities along the shoreline corresponds with the flooding of the Persian Gulf basin around 8,000 years ago," Rose said. "These new colonists may have come from the heart of the Gulf, displaced by rising water levels that plunged the once fertile landscape beneath the waters of the Indian Ocean."

Historical sea level data show that, prior to the flood, the Gulf basin would have been above water beginning about 75,000 years ago. And it would have been an ideal refuge from the harsh deserts surrounding it, with fresh water supplied by the Tigris, Euphrates, Karun, and Wadi Baton Rivers, as well as by underground springs. When conditions were at their driest in the surrounding hinterlands, the Gulf Oasis would have been at its largest in terms of exposed land area. At its peak, the exposed basin would have been about the size of Great Britain, Rose says.

Evidence is also emerging that modern humans could have been in the region even before the oasis was above water. Recently discovered archaeological sites in Yemen and Oman have yielded a stone tool style that is distinct from the East African tradition. That raises the possibility that humans were established on the southern part of the Arabian Peninsula beginning as far back as 100,000 years ago or more, Rose says. That is far earlier than the estimates generated by several recent migration models, which place the first successful migration into Arabia between 50,000 and 70,000 years ago.

The Gulf Oasis would have been available to these early migrants, and would have provided "a sanctuary throughout the Ice Ages when much of the region was rendered uninhabitable due to hyperaridity," Rose said. "The presence of human groups in the oasis fundamentally alters our understanding of human emergence and cultural evolution in the ancient Near East."

It also hints that vital pieces of the human evolutionary puzzle may be hidden in the depths of the Persian Gulf.

Chicago Journals




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