Cassini Is On The Trail Of A Runaway Mystery

Source:

http://www.sciencedaily.com/releases/2007/10/071008145004.htm

Science Daily — NASA scientists are on the trail of Iapetus' mysterious dark side, which seems to be home to a bizarre "runaway" process that is transporting vaporized water ice from the dark areas to the white areas of the Saturnian moon.

This "thermal segregation" model may explain many details of the moon's strange and dramatically two-toned appearance, which have been revealed exquisitely in images collected during a recent close flyby of Iapetus by NASA's Cassini spacecraft.
Infrared observations from the flyby confirm that the dark material is warm enough (approximately minus 230 degrees Fahrenheit or 127 Kelvin) for very slow release of water vapor from water ice, and this process is probably a major factor in determining the distinct brightness boundaries.
"The side of Iapetus that faces forward in its orbit around Saturn is being darkened by some mysterious process," said John Spencer, Cassini scientist with the composite infrared spectrometer team from the Southwest Research Institute, Boulder, Colo.
Using multiple instruments on Cassini, scientists are piecing together a complex story to explain the bright and dark faces of Iapetus. But yet to be fully understood is where the dark material is coming from. Is it native or from outside the moon? It has long been hypothesized that this material did not originate from within Iapetus, but instead was derived from other moons orbiting at a much greater distance from Saturn in a direction opposite to Iapetus.
Scientists are now converging on the notion that the darkening process in fact began in this manner, and that thermal effects subsequently enhanced the contrast to what we see today.
"It's interesting to ponder that a more than 30-year-old idea might still help explain the brightness difference on Iapetus," said Tilmann Denk, Cassini imaging scientist at the Free University in Berlin, Germany. "Dusty material spiraling in from outer moons hits Iapetus head-on, and causes the forward-facing side of Iapetus to look different than the rest of the moon."
Once the leading side is even slightly dark, thermal segregation can proceed rapidly. A dark surface will absorb more sunlight and warm up, explains Spencer, so the water ice on the surface evaporates. The water vapor then condenses on the nearest cold spot, which could be Iapetus's poles, and possibly bright, icy areas at lower latitudes on the side of the moon facing in the opposite direction of its orbit. So the dark stuff loses its surface ice and gets darker, and the bright stuff accumulates ice and gets brighter, in a runaway process.
Scientists say the result is that there are virtually no shades of gray on Iapetus. There is only white and very dark.
Ultraviolet data also show a non-ice component in the bright, white regions of Iapetus. Spectroscopic analysis will reveal whether the composition of the material on the dark hemisphere is the same as the dark material that is present within the bright terrain.
"The ultraviolet data tell us a lot about where the water ice is and where the non-water ice stuff is. At first glance, the two populations do not appear to be present in the pattern we expected, which is very interesting," said Amanda Hendrix, Cassini scientist on the ultraviolet imaging spectrograph team at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
Because of the presence of very small craters that excavate the bright ice beneath, scientists also believe that the dark material is thin, a result consistent with previous Cassini radar results. But some local areas may be thicker. The dark material seems to lie on top of the bright region, consistent with the idea that it is a residual left behind by the sublimated water ice.
Some other mysteries are coming together. There are more data on the signature mountain ridge that gives Iapetus its "walnut" appearance. In some places it appears subdued. One big question that remains is why it does not go all the way around.
Was it partially destroyed after it formed, or did it never extend all the way around the moon? Scientists have ruled out that it is a youthful feature because it is pitted with craters, indicating it is old. And the ridge looks too solid and competent to be the result of an equatorial ring around the moon collapsing onto its surface. The ring theory cannot explain features that look like tectonic structures in the new high resolution images.
Over the next few months, scientists hope to learn more about Iapetus' mysteries.
New Iapetus images, temperature maps and other visuals on Iapetus are available at: http://saturn.jpl.nasa.gov/ and http://www.nasa.gov/cassini .
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Science Mission Directorate, Washington, D.C.
Note: This story has been adapted from material provided by NASA/Jet Propulsion Laboratory.

Fausto Intilla

www.oloscience.com

Multiwavelength Images Of Distant Universe Now Available On Google Sky

Source:

http://www.sciencedaily.com/releases/2007/10/071003130840.htm

Science Daily — A massive project to map a distant region of the Universe in multiple wavelengths--from x-rays through ultraviolet, visible, infrared, and radio waves--is currently releasing its data to both fellow scientists and the general public. It is the first data release from the AEGIS survey and the first release of multiwavelength data to take advantage of the capabilities of Google Sky, a new feature of Google Earth.

AEGIS--the All-wavelength Extended Groth Strip International Survey--combines the efforts of nearly 100 researchers from around the world observing the same small region of sky in all available wavelengths of the electromagnetic spectrum. The target area, called the Extended Groth Strip, covers an area the width of four full moons that is a hop, skip and jump from the end of the Big Dipper's handle. The AEGIS region has now been surveyed more intensively and with more telescopes than any other region of the sky.
"We are still sorting through this treasure trove to discover the many gems of information it contains," said Sandra Faber, University Professor and chair of astronomy and astrophysics at the University of California, Santa Cruz. Faber worked with Jeffrey Newman of the University of Pittsburgh, Shui Kwok of the W. M. Keck Observatory in Hawaii, UCSC graduate student Genevieve Graves, and many other members of the AEGIS team to coordinate the data release through Google Sky.
"We are looking back to a time when the universe was more than half its current age and when galaxies were forming most of their stars," says Professor Kirpal Nandra, from the Department of Physics and who is leading the project from Imperial College London. He added: "With the X-ray images we are looking at black holes, which are at the centre of galaxies, to try to work out how the growth of black holes is linked to the growth of the galaxy itself."
"It is clear that serving astronomical data through Google Sky is going to revolutionize the way astronomers communicate, both among themselves and with the public," Faber said. "AEGIS is proud and pleased to be the pathfinder dataset for Google Sky's new multiwavelength capabilities."
Color images from four different satellite telescopes, as well as numerous data catalogs, from x-ray to radio wavelengths, giving brightnesses and distances of tens of thousands of galaxies are now available. Google Earth's new Sky feature provides a fast and powerful access tool for astronomical data similar to what the popular Google Earth software has provided for terrestrial data.
"AEGIS images projected onto the celestial sphere show how it would look with infrared, ultraviolet, or x-ray eyes," Faber said. "Some galaxies look brighter at certain wavelengths than others, which carries important information about their composition and the processes occurring within them."
The rapid browsing abilities of Google Sky provide a new way to compare many views of a single galaxy or a set of galaxies instantly. For researchers, it is a powerful tool for exploring AEGIS's massive data sets. The AEGIS collaboration is also making all of its data available on its website, so that researchers can download it directly.
Of the four color images in the first AEGIS data release, the most detailed is a visible-light image stitched together from 63 separate pointings of the Hubble Space Telescope. This image forms the base map in Google Sky. Stretching twice the width of the full Moon, it is the largest unbroken color mosaic ever made with Hubble and contains images of approximately 50,000 faraway galaxies. Light has traveled for more than 10 billion years from the most distant ones, giving us pictures of them as they looked long ago, more than three-quarters of the way back to the Big Bang. The exquisite detail of the Hubble images shows infant and adolescent galaxies as they began to form.
The second image shows the same galaxies through the ultraviolet eyes of NASA's Galaxy Evolution Explorer (GALEX) satellite. Ultraviolet wavelengths are shorter and bluer than those of visible light. Massive, hot young stars that are just forming produce ultraviolet light in abundance. Brightness in the GALEX image therefore provides a measure of the rate at which each galaxy is forming stars. Galaxies that contain relatively few hot, young stars or that are obscured by either their own dust or diffuse gas along our line of sight will appear redder in the GALEX image.
The third view is a mosaic of images taken with the Infrared Array Camera on NASA's Spitzer Space Telescope, the last mission in NASA's Great Observatory series. Near-infrared brightness is closely related to the total number of stars in a galaxy, while the colors of a galaxy as seen through infrared eyes reveal information on both its contents (stars and dust) and its distance from us.
The fourth image was produced with data from NASA's Chandra X-ray Observatory. In the objects seen by Chandra, highly energetic x-ray radiation has been produced when gas is spiralling into a supermassive black hole, like those believed to lie at the center of almost every galaxy. Many of the x-ray-emitting objects lie buried within otherwise normal-looking galaxies. In the x-ray images, the bluest objects are the ones most obscured by gas within their host galaxies.
In the objects seen by Chandra, X-ray radiation has been produced when gas is spiralling into a super massive black hole, like those believed to lie at the centre of almost every galaxy. Many of the X-ray emitting objects lie buried within otherwise normal-looking galaxies. In these X-ray images, the bluest objects are the ones most obscured by gas within their host galaxies, according to researchers at Imperial College in London.
In combination, these images simultaneously measure the sizes and shapes of galaxies, their current rates of star formation, the total number of stars each galaxy has already formed, and the rate at which a black hole at its center is actively accreting matter. All of this information provides separate clues to help scientists understand the evolution of galaxies over the past 10 billion years.
These images from space-based telescopes are tied together by the spectra of nearly 15,000 AEGIS galaxies taken with the Keck II Telescope in Hawaii as part of the DEEP2 Galaxy Redshift Survey, led by Faber and Marc Davis of UC Berkeley. Among other information, these spectra enable astronomers to determine distances to these objects, which is crucial for distinguishing small galaxies in the foreground from giant galaxies that appear faint because they are so far away. Once they have determined the distance to a galaxy, astronomers know how far back in time light left it. The most distant galaxies in the AEGIS survey are seen as they looked only a few billion years after the Big Bang.
With the Sky feature in Google Earth, users can pan and zoom around all of these pictures of the sky to select individual galaxies for closer inspection. By adjusting the transparency of each image, the user can focus on only one of the AEGIS images at a time, or look at a combination (e.g., the GALEX image superimposed on Hubble). Clicking on galaxies in AEGIS catalogs brings up their distances and intrinsic properties. A further mouse click links the user to the Keck spectrum and additional information being used for AEGIS science studies.
This first data release from AEGIS is only the first step. Later releases will feature images taken at far-infrared and radio wavelengths. A master catalog is being prepared that combines information from all of AEGIS's many views of the sky. As future images are prepared, they and the growing data catalogs will all be linked through Google Sky.
The AEGIS web site gives more information about the survey, science results to date, and links to additional images and data that can be downloaded. The many windows on the universe provided by AEGIS have already produced a variety of new results on the evolution of galaxies, and many more new findings from the AEGIS team will appear soon, according to Newman.
"With this public release of both interactive images and the underlying data catalogs, the full astronomical community will now be able to take advantage of this powerful new dataset," he said.
The AEGIS teams that contributed images and data for this release include the Hubble team led by Marc Davis of UC Berkeley; the Chandra team lead by Kirpal Nandra of Imperial College, London; the Spitzer team led by Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics; and the GALEX team led by Chris Martin of the California Institute of Technology. Funding for the AEGIS collaboration was provided by the National Science Foundation and NASA.
Images are available at: http://earth.google.com/gallery/index.html
Note: This story has been adapted from material provided by University of California, Santa Cruz.

Fausto Intilla

www.oloscience.com

Dark Matter Of The Universe Has A Long Lifetime

Source:

http://www.sciencedaily.com/releases/2007/10/071001112906.htm

Science Daily — New research from the Niels Bohr Institute presents new information that adds another piece of knowledge to the jigsaw puzzle of the dark mystery of the universe -- dark matter.

The universe consists not just of visible celestial bodies, stars, planets and galaxies. It also has a mystical fellow player -- dark matter. The astronomers can measure that the dark matter exists in big quantities but no one knows what it is, nobody has seen it. It does not emit light and it does not reflect light. It is invisible. It is a mystery and the researchers have many theories.
The dark matter has caused the researchers headaches for decades since it was detected in the 1970s, and there is intense research into the phenomena. It is invisible but it has got mass, and thus it has got gravitation that can be measured. By analysing the galaxies it is possible to weigh them, and it turns out that by far the greatest matter of the collective mass of the galaxy is dark matter.
Just like stars get together in galaxies, the galaxies get together in clusters of galaxies of up to several thousand galaxies. The astrophysicist Signe Riemer-Sørensen, PhD student at the Niels Bohr Institute, has analysed two clusters of galaxies that collide.
Colliding clusters of galaxies
When the two clusters of galaxies meet neither the galaxies nor the dark matter collide. However, about 12 per cent of the mass of the cluster of galaxies consists of huge clouds of gas and dust and these clouds collide. The gas clouds are hot and emit x-ray that can be observed, and it is possible to see how the clouds are actually pushed out of the two clusters of galaxies at the collision. When the clouds of gas collide they become even hotter and emit more x-ray so that a whole chock front of warn gas is generated.
Observations indicate that the dark matter can be a new and still undetected type of particle. Among the suggestions for the dark matter, are particles that when they decay they emit x-ray. One is the so called axions that are particles which is explained in theories with extra dimensions. So to be able to look for x-ray from dark matter the researchers are looking in places where there is a big concentration of dark matter, but no gas. Such places are found in the two colliding clusters of galaxies where the gas clouds have been pushed out at the collision.
Signe Riemer-Sørensen has analysed the one of the two clusters of galaxies that are in the process of colliding. The analyses show that it is a very heavy cluster with many galaxies, and measurement of the gravitation show that there is a very big amount of dark matter, up to 85 per cent of the collective mass. However, no x-ray of any consequence was measured.
When the dark matter does not emit significant x-ray it is possible to calculate an upper limit to how quickly the particles decay and thus calculate their lifetime. The result is that if axions are to be the dark matter they must have a life span that is longer that 3.000.000 billion years. In that case there is not very much dark matter that has decayed yet if it was formed 13.7 billion years ago. The conclusion is that dark matter has a very, very long lifetime.
The research has just been published in the scientific journal Physical Review Letters.
Note: This story has been adapted from material provided by University of Copenhagen.

Fausto Intilla

www.oloscience.com

Earth-like Planet Forming In Nearby Star System, Astronomers Believe

Source:

http://www.sciencedaily.com/releases/2007/10/071003130744.htm

Science Daily — An Earth-like planet is likely forming 424 light-years away in a star system called HD 113766, say astronomers using NASA's Spitzer Space Telescope.

Scientists have discovered a huge belt of warm dust – enough to build a Mars-size planet or larger – swirling around a distant star that is just slightly more massive than our sun.
The dust belt, which they suspect is clumping together into planets, is located in the middle of the system's terrestrial habitable zone. This is the region around a star where liquid water could exist on any rocky planets that might form. Earth is located in the middle of our sun's terrestrial habitable zone.
At approximately 10 million years old, the star is also at just the right age for forming rocky planets.
"The timing for this system to be building an Earth is very good," says Dr. Carey Lisse, of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. "If the system was too young, its planet-forming disk would be full of gas, and it would be making gas-giant planets like Jupiter instead. If the system was too old, then dust aggregation or clumping would have already occurred and all the system's rocky planets would have already formed."
According to Lisse, the conditions for forming an Earth-like planet are more than just being in the right place at the right time and around the right star – it's also about the right mix of dusty materials.
Using Spitzer's infrared spectrometer instrument, he determined that the material in HD 113766 is more processed than the snowball-like stuff that makes up infant solar systems and comets, which are considered cosmic "refrigerators" because they contain pristine ingredients from the early solar system. However, it is also not as processed as the stuff found in mature planets and the largest asteroids. This means the dust belt must be in a transitional phase, when rocky planets are just beginning to form.
How do scientists know the material is more processed than that of comets? From missions like NASA's Deep Impact – in which an 820-pound impactor spacecraft collided with comet Tempel 1 – scientists know that early star systems contain a lot of fragile organic material. That material includes polycyclic aromatic hydrocarbons (carbon-based molecules found on charred barbeque grills and automobile exhaust on Earth), water ice, and carbonates (chalk). Lisse says that HD 113766 does not contain any water ice, carbonates or fragile organic materials.
From meteorite studies on Earth, scientists also have a good idea of what makes up asteroids – the more processed rocky leftovers of planet formation. These studies tell us that metals began separating from rocks in Earth's early days, when the planet's body was completely molten. During this time, almost all the heavy metals fell to Earth's center in a process called "differentiation." Lisse says that, unlike planets and asteroids, the metals in HD 113766 have not totally separated from the rocky material, suggesting that rocky planets have not yet formed.
"The material mix in this belt is most reminiscent of the stuff found in lava flows on Earth. I thought of Mauna Kea material when I first saw the dust composition in this system – it contains raw rock and is abundant in iron sulfides, which are similar to fool's gold," says Lisse, referring to a well-known Hawaiian volcano.
"It is fantastic to think we are able to detect the process of terrestrial planet formation. Stay tuned — I expect lots more fireworks as the planet in HD113766 grows," he adds.
Lisse's article, Circumstellar Dust Created by Terrestrial Planet Formation in HD 113766, will be published in an upcoming issue of Astrophysical Journal. He will also present his findings at the upcoming meeting of the American Astronomical Society Division for Planetary Sciences in Orlando, Fla. Lisse's research was funded through a Johns Hopkins Applied Physics Laboratory Stuart S. Janney Fellowship and a Spitzer Space Telescope guest observer grant.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.
The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL.
Note: This story has been adapted from material provided by Johns Hopkins University.

Fausto Intilla

www.oloscience.com

Disc Of Silicates Found In Heart Of Magnificent Ant Nebula

Source:

http://www.sciencedaily.com/releases/2007/09/070927113205.htm

Science Daily — Using ESO's Very Large Telescope Interferometer and its unique ability to see small details, astronomers have uncovered a flat, nearly edge-on disc of silicates in the heart of the magnificent Ant Nebula. The disc seems, however, too 'skinny' to explain how the nebula got its intriguing ant-like shape.
The Ant Nebula is one of the most striking planetary nebulae known. Planetary nebulae - whose name arises because most are spherical and looked like planets when they were first discovered through older, less powerful telescopes - are glowing structures of gas cast off by solar-like stars at the ends of their lives. The morphology of the Ant Nebula - a bright core, three nested pairs of bipolar lobes and a ring-like outflow - is so unique that it was nicknamed the 'Chamber of Horrors' of planetary nebulae in the late 1950s.
But how can a spherical star produce such complex structures? The answer, many astronomers think, requires understanding of the discs surrounding the central star. By their nature, these discs bear witness to the phenomena that lead to the asymmetrical structures of planetary nebulae.
"The challenge is to actually detect these discs," explains team leader Olivier Chesneau, from the Observatoire de la Côte d'Azur, France. "Most astronomical instruments do not have a sharp enough view to find, let alone study them. The Very Large Telescope Interferometer however, with its exceptionally high spatial resolution, is a powerful disc-hunter."
The disc of the Ant Nebula, which cannot be detected with a single 8.2-m VLT Unit Telescope, was uncovered in the interferometric mode where two 8.2-m Unit Telescopes were used to combine light, through the MID-infrared Interferometric instrument (MIDI). The observations reveal a flat, nearly edge-on disc whose major axis is perpendicular to the axis of the bipolar lobes.
The disc extends from about 9 times the mean distance between the Earth and the Sun (9 Astronomical Units or 9 AU) to more than 500 AU. At the distance of the Ant Nebula, this corresponds to having detected structures that subtend an angle of only 6 milli-arcseconds. This is similar to distinguishing a two-storey building on the Moon.
The dust mass stored in the disc appears to be only one hundred thousandth the mass of the Sun and is a hundred times smaller than the mass found in the bipolar lobes.
"We must therefore conclude that the disc is too light to have a significant impact on the outflowing material and cannot explain the shape of the Ant Nebula", says Chesneau. "Instead, it looks more like this disc is some remnant of the material expelled by the star."
The observations also provide unquestionable evidence that the disc is primarily composed of amorphous silicate. "This," says Chesneau, "most likely indicates that the disc is young, perhaps as young as the planetary nebula itself."
The astronomers favour the possibility that the large quantity of material in the lobes was propelled by several large-scale events, triggered with the help of a cool stellar companion. The solution of the mystery thus resides in the core of the system, and requires better characterisation of the hot central star and its putative companion, currently hidden from our view by the dusty disc.
The results are presented in a Letter to the Editor published by the research journal Astronomy and Astrophysics ("A silicate disk in the heart of the Ant" by O. Chesneau et al.).
The team is composed of O. Chesneau and A. Spang (Observatoire de la Côte d'Azur, France), F. Lykou, E. Lagadec, and A.A. Zijlstra (University of Manchester, UK), B. Balick (University of Washington, Seattle, USA), M. Matsuura (NAOJ, Tokyo, Japan), N. Smith (University of California, USA), and S. Wolf (Max-Planck-Institute for Astronomy, Heidelberg, Germany).
Note: This story has been adapted from material provided by ESO.

Fausto Intilla
www.oloscience.com

Into The Chrysalis: VLT Interferometer Detects Disc Around Aged Star

Source:

http://www.sciencedaily.com/releases/2007/09/070927113202.htm

Science Daily — A team of European astronomers has used ESO's Very Large Telescope Interferometer and its razor-sharp eyes to discover a reservoir of dust trapped in a disc that surrounds an elderly star. The discovery provides additional clues about the shaping of planetary nebulae.

In the last phases of their life, stars such as our Sun evolve from a red giant which would engulf the orbit of Mars to a white dwarf, an object that is barely larger than the Earth. The transition is accomplished by the shedding of a huge envelope of gas and dust that sparkles in many colours, producing a most spectacular object: a planetary nebula. The celestial chrysalis becomes a cosmic butterfly.
This metamorphosis, rapid in terms of the star's lifetime, is rather complex and poorly understood. In particular, astronomers want to understand how a spherical star can produce a great variety of planetary nebulae, some with very asymmetrical shapes.
A team of scientists therefore embarked upon the study of a star which is presently on its way to becoming a cosmic butterfly. The star, V390 Velorum, is 5000 times as bright as our Sun and is located 2,600 light-years away. It is also known to have a companion that accomplishes its ballet in 500 days.
Astronomers postulate that elderly stars with companions possess a reservoir of dust that is thought to play a lead role in the final chapters of their lives. The shape and structure of these reservoirs remain, however, largely unknown.
To scrutinize the object with great precision, the astronomers linked observations taken with ESO's powerful interferometric instruments, AMBER and MIDI, at the Very Large Telescope Interferometer. In particular, they combined, using AMBER, the near-infrared light of three of VLT's 8.2-m Unit Telescopes. "Only this triple combination of powerful telescopes allows us to pinpoint the position and the shape of the dusty reservoir on a milli-arcsecond scale," explains Pieter Deroo, lead-author of the paper that presents these results in the research journal Astronomy and Astrophysics.
These observations clearly demonstrate that the dust present around the star cannot be distributed in a spherical shell. "This shows that whatever mechanism is shaping asymmetric planetary nebulae is already present prior to the metamorphosis taking place," says Hans Van Winckel, member of the team.
The astronomers found indeed evidence for a disc extending from 9 Astronomical Units* to several hundreds of AU. "This disc is found around a star that is in a very brief phase of its life - just a blink of an eye over the star's lifespan of billions of years - but this phase is very important," says Deroo. "It is in this period that a huge morphological change occurs, leading to the creation of a planetary nebula," he adds.
The very high spatial resolution measurements allowed the astronomers to decouple the unresolved contribution of the central star from the resolved disc emission. Even the very inner structure of the disc as well as its orientation and inclination could be determined. The observations probe the physical nature of the disc and reveal that the dust in the inner rim is extremely hot and puffed up. The disc is circumbinary as it surrounds both stars.
Dust processing (coagulation, crystallisation) is found to be very efficient in this circumbinary disc, despite the rather short evolutionary timescales involved. The disc around this evolved object is very similar to those around young stellar objects, in which planets are formed.
"The combination of MIDI and AMBER on ESO's VLTI is an extremely powerful and perhaps unique tool to study the geometry of the material around stars," concludes Van Winckel.
It looks like it is the season for disc 'hunting': the detection of a dusty disc in the notable Ant Nebula was also just announced (see ESO 42/07).
The results presented here are reported in a Letter to the Editor to appear in the research journal Astronomy and Astrophysics ("AMBER and MIDI interferometric observations of the post-AGB binary IRAS 08544-4431: the circumbinary disc resolved", by P. Deroo et al.).
The team includes Pieter Deroo, Bram Acke, Tijl Verhoelst, and Hans Van Winckel (K. U. Leuven, Belgium), Carsten Dominik (University of Amsterdam, the Netherlands), and Eric Tatulli (INAF-Observatorio di Arcetri, Firenze, Italy).
*One Astronomical Unit (AU) is the mean distance between the Earth and the Sun. It corresponds to 149.6 million kilometres. For comparison, Saturn is 10 AU away from the Sun.
Note: This story has been adapted from material provided by European Organisation For Astronomical Research In The Southern Hemisphere.

Fausto Intilla

www.oloscience.com

Dilaton Could Affect Abundance Of Dark Matter Particles

Source:

http://www.sciencedaily.com/releases/2007/10/071002084628.htm

Science Daily — The amount of dark matter left over from the early universe may be less than previously believed. New research shows that the "relic abundance" of stable dark matter particles such as the neutralino may be reduced as compared to standard cosmology theories due to the effects of the "dilaton", a particle with zero spin in the gravitational sector of strings.
Nikolaos Mavromatos of King's College London and colleagues in Athens and Texas obtained their result by studying a special "off-shell" time-dependent term (due to the dilaton) in the Boltzmann equation that describes the evolution of hot matter density as the Universe cooled down. "The formalism that this work used was developed in partial collaboration with John Ellis of CERN and Vasiliki Mitsou of IFIC, Valencia, and is a version of 'non-critical string theory'", said Mavromatos.
Dark matter is fundamentally different from normal, luminous matter and is invisible to modern telescopes, giving off no light or heat. It appears to interact with normal matter only through gravity. Most cosmologists believe dark matter, currently thought to make up 95% of all matter in the universe, plays a crucial role in how large structures such as galaxies emerged after the Big Bang.
All the matter and radiation in the universe is thought to have been created by the Big Bang. The radiation stopped interacting with the matter some 400,000 years later -- when the universe had cooled down enough for electrons and protons to form hydrogen atoms. The density of dark matter particles such as the neutralino (a dark matter candidate favoured by many of the current "supersymmetric" approaches to particle physics) was therefore "frozen" at this time -- the so-called relic abundance.
The researchers say that the neutralino relic abundance is reduced by as much as a factor of ten in their models due to dilaton effects, as compared to standard cosmology theories. In contrast, the relic abundance of "ordinary" matter, which makes up stars, planets and humans, is only slightly diluted. The new model also agrees with the established model of nucleosynthesis (the way in which light elements were created during the first few minutes of the universe).
The new result is important for both cosmology and particle physics, says Mavromatos. Indeed, such non-equilibrium string cosmology models are on an equal footing with the standard cosmological cold dark matter model (called Lambda-CDM). For particle physics, the findings are relevant for future supersymmetric searches in colliders such as the Large Hadron Collider, due to come on-line at CERN early next year. The supersymmetric theory, one of the facets of string theory, postulates that every particle has a massive "shadow" particle partner.
Article: Dilaton and off-shell (non-critical string) effects in Boltzmann equation for species abundances, A.B. Lahanas et al., PMC Physics A (in press)
Note: This story has been adapted from material provided by BioMed Central.

Fausto Intilla
www.oloscience.com