Monday, July 5, 2010


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An international team including scientists from Princeton University has detected subatomic particles deep within the Earth's interior. The discovery could help geologists understand how reactions taking place in the planet's interior affect events on the surface such as earthquakes and volcanoes. Someday, scientists may know enough about the sources and flow of heat in the Earth to predict events like the recent volcanic eruption in Iceland.

The finding, made by the Borexino Collaboration at the Gran Sasso National Laboratory of the Italian Institute of Nuclear Physics, was reported in a paper published in the April issue of Physics Letters B. The work builds on earlier evidence of so-called "geoneutrinos" obtained during a Japanese experiment in 2005.

"This is an important result," said Frank Calaprice, a professor of physics at Princeton and one of the study's authors. "It shows that geoneutrinos have been detected and firmly establishes a new tool to study the interior of the Earth."

Neutrinos, which are chargeless, inert, fundamental particles, are emitted by the sun and cosmic rays entering the Earth's atmosphere. Geoneutrinos are antineutrinos -- neutrinos' antimatter counterparts. Geoneutrinos originate from the radioactive decay of uranium, thorium and potassium in the Earth's crust and mantle -- the thick layer extending to 1,800 miles below the surface.

At laboratories like Gran Sasso, researchers are using instruments that act as geoneutrino "telescopes," looking into the Earth's interior by detecting these curious particles.

Scientists expect that geoneutrinos will aid them in better identifying what constitutes matter deep within the Earth. "It's a very significant discovery and holds much promise for better understanding the composition of the Earth and how the Earth operates," said Thomas Duffy, a professor of geosciences at Princeton, who was not involved in the research.

Earth scientists would like to know more about the crucial role that decaying elements such as uranium and thorium play in heating up the Earth and causing convection in its mantle -- the slow, steady flow of hot rock in the interior carrying heat from great depths to the Earth's surface. Convection, in turn, drives plate tectonics and all the accompanying dynamics of geology seen from the surface -- continents moving, seafloor spreading, volcanoes erupting and earthquakes occurring. No one knows whether radioactive decay dominates the heating action or is just a player among many factors.

The origin of the power produced within the Earth is one of the fundamental questions of geology, according to Calaprice. The definite detection of geoneutrinos by the Borexino experiment confirms that radioactivity contributes a significant fraction -- possibly most -- of the power, he said.

The Borexino experiment actually was designed to detect low-energy solar neutrinos, not geoneutrinos. "As we were building the experiment, we realized we had the capability of detecting particles that were coming at us from the radioactivity deep inside the Earth," said Cristiano Galbiati, an assistant professor of physics and another of the 13 Princeton collaborators among the 88 scientists involved in the research.

The Borexino project is located nearly a mile below the surface of the Gran Sasso mountain about 60 miles outside of Rome -- an ideal spot for studying neutrinos because the rock shields the detector from other types of radiation and particles that would overwhelm the sensing device. Much of the Borexino experiment is a process of eliminating the "noise" of background radiation.

Neutrinos are notoriously difficult to detect because they usually pass straight through matter, rarely interacting with it. The detector is composed of a nylon sphere containing 1,000 tons of a hydrocarbon liquid. An array of ultrasensitive photodetectors is aimed at the sphere that is encased within a stainless steel sphere. All of this is surrounded by 2,400 tons of highly purified water held within another steel sphere measuring 59 feet.

Solar neutrinos produce one type of signal when they come into contact with the detector, and geoneutrinos produce another type. Because there are a thousand times fewer geoneutrinos striking the detector, there are only a few events that occur per year. The paper describes two years of results, running up to December 2009. The experiment is continuing.

The importance of geoneutrinos was pointed out by scientists in the 1960s, and a seminal study by Lawrence Krauss, Sheldon Glashow and David Schramm in 1994 laid the foundation for the field. In 2005, a Japan-U.S. collaboration called KamLAND operating an experiment at a mine in Japan reported an excess of low-energy "antineutrinos."

Scientists can envision a day when a series of geoneutrino-detecting facilities, located at strategic spots around the globe, can sense particles to get a detailed understanding of the Earth's interior and the source of its internal heat. This data could provide enough information to predict the occurrence of events such as volcano eruptions and earthquakes.

(Photo: Paolo Lombardi INFN-MI)

Princeton University


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For the first time, a team of astronomers has succeeded in investigating the earliest phases of the evolutionary history of our home Galaxy, the Milky Way. The scientists, from the Argelander Institute for Astronomy at Bonn University and the Max-Planck Institute for Radioastronomy in Bonn, deduce that the early Galaxy went from smooth to clumpy in just a few hundred million years. The team publish their results in the journal Monthly Notices of the Royal Astronomical Society.

Led by Professor Dr. Pavel Kroupa, the researchers looked at the spherical groups of stars (globular clusters) that lie in the halo of the Milky Way, outside the more familiar spiral arms where the Sun is found. They each contain hundreds of thousands of stars and are thought to have formed at the same time as the ‘proto-Galaxy’ that eventually evolved into the Galaxy we see today.

Globular star clusters can be thought of as fossils from the earliest period of the history of the Galaxy and the astronomers found that they left a hint of the conditions under which they formed. The stars of the clusters condensed out of a cloud of molecular gas (relatively cool hydrogen), not all of which was used up in their formation. The residual gas was expelled by the radiation and winds coming from the freshly hatched population of stars.

“Due to this ejection of gas, the globular clusters expanded and thereby lost the stars that formed at their boundaries. This means that the present shape of the clusters was directly influenced by what happened in the early days of their existence”, explains Michael Marks, PhD student of Professor Kroupa and lead author on the new paper.

The clusters were also shaped by the forming Milky Way and the Bonn scientists calculated exactly how the proto-Galaxy affected its smaller neighbours. Their results show that the gravitational forces exerted on the star clusters by the proto-Milky Way appear to increase with the metal content of their member stars (in astronomy ‘metals’ in stars are elements heavier than helium).

“The amount of e.g. iron in a star is therefore an age indicator. The more recently a star cluster was born, the higher the proportion of heavy elements it contains”, adds Marks. But since the globular clusters are more or less the same age, these age differences can't be large. In order to explain the variation in the forces exerted on different globular clusters, the structure of the Milky Way had to change rapidly within a short time.

The giant gas cloud from which the Milky Way formed had to evolve from an overall smooth structure into a clumpy object in less than a few hundred million years in order to increase the strength of the forces significantly. This timespan corresponds to the astronomically short duration in which the proto-galaxy-sized gas cloud collapsed under its own gravity. In parallel, the globular clusters formed successively within the collapsing cloud. The material from which the somewhat younger globular clusters formed and which according to the results of this investigation felt stronger attractive forces, was previously enriched with heavy elements by fast-evolving stars in the older clusters.

Prof. Kroupa summarises their results. “In this picture we can elegantly combine the observational and theoretical results and understand why later forming, more metal-rich clusters experienced stronger force fields. On the back of this work, for the first time we have a detailed insight into the earliest evolutionary history of our Galaxy”.

(Photo: The Hubble Heritage Team / AURA / STScI / NASA)

Royal Astronomical Society


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A team of scientists from the Instituto Astrofísica de Canarias (IAC) and the University of Texas has succeeded in identifying one of the most complex organic molecules yet found in the material between the stars, the so-called interstellar medium. The discovery of anthracene could help resolve a decades-old astrophysical mystery concerning the production of organic molecules in space. The researchers report their findings in the journal Monthly Notices of the Royal Astronomical Society.

'We have detected the presence of anthracene molecules in a dense cloud in the direction of the star Cernis 52 in Perseus, about 700 light years from the Sun,' explains Susana Iglesias Groth, the IAC researcher heading the study.

In her opinion, the next step is to investigate the presence of amino acids. Molecules like anthracene are prebiotic, so when they are subjected to ultraviolet radiation and combined with water and ammonia, they could produce amino acids and other compounds essential for the development of life

'Two years ago,' says Iglesias, 'we found proof of the existence of another organic molecule, naphthalene, in the same place, so everything indicates that we have discovered a star formation region rich in prebiotic chemistry.' Until now, anthracene had been detected only in meteorites and never in the interstellar medium. Oxidized forms of this molecule are common in living systems and are biochemically active. On our planet, oxidized anthracene is a basic component of aloe and has anti-inflammatory properties.

The new finding suggests that a good part of the key components in terrestrial prebiotic chemistry could be present in interstellar matter.

Since the 1980s, hundreds of bands found in the spectrum of the interstellar medium, known as diffuse spectroscopic bands, have been known to be associated with interstellar matter, but their origin has not been identified until now. This discovery indicates that they could result from molecular forms based on anthracene or naphthalene. Since they are widely distributed in interstellar space, they might have played a key role in the production of many of the organic molecules present at the time of the formation of the Solar System.

The results are based on observations carried out at the William Herschel Telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands and with the Hobby-Eberly Telescope in Texas in the United States.

(Photo: Gaby Perez and Susana Iglesias-Groth)

Royal Astronomical Society




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