Dark Matter Could Transfer Energy in the Sun

Dark Matter Could Transfer Energy in the Sun

  10:05:00 AM    Science Lover

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Researchers from the Institute for Corpuscular Physics (IFIC) and other European groups have studied the effects of the presence of dark matter in the Sun. According to their calculations, low mass dark matter particles could be transferring energy from the core to the external parts of the Sun, which would affect the quantity of neutrinos that reach Earth.

Scientists believe that the majority of the dark matter 
particles gather together in the centre of the Sun, 
but in their elliptic orbits they also travel to the outer
part, interacting and exchanging with the solar atoms. 
In this way, the WIMPs transport the energy from the 
burning central core to the cooler peripheral
parts. (Credit: Hinode JAXA/NASA/PPARC)

"We assume that the dark matter particles interact weakly with the Sun's atoms, and what we have done is calculate at what level these interactions can occur, in order to better describe the structure and evolution of the Sun," Marco Taoso, researcher at the IFIC, a combined centre of the Spanish National Research Council and the University of Valencia, explains.

The astrophysical observations suggest that our galaxy is situated in a halo of dark matter particles. According to the models, some of these particles, the WIMPs (Weakly Interacting Massive Particles) interact weakly with other normal ones, such as atoms, and could be building up on the inside of stars. The study, recently published in the journal Physical Review D, carries out an in-depth study of the case of the Sun in particular.

"When the WIMPs pass through the Sun they can break up the atoms of our star and lose energy. This prevents them from escaping the gravitational force of the Sun which captures them, and they become trapped, orbiting inside it, with no way of escaping," the researcher points out.

The dark matter cools down the Sun's core

Scientists believe that the majority of the dark matter particles gather together in the centre of the Sun, but in their elliptic orbits they also travel to the outer part, interacting and exchanging with the solar atoms. In this way, the WIMPs transport the energy from the burning central core to the cooler peripheral parts.

"This effect produces a cooling down of the core, the region from where the neutrinos originate due to the nuclear reactions of the Sun," Taoso points out. "And this corresponds to a reduction in the flux of solar neutrinos, since these depend greatly on the temperature of the core."

The neutrinos that reach Earth can be measured by means of different techniques. These data can be used to detect the modifications of the solar temperature caused by the WIMPs. The transport of energy by these particles depends on the likelihood of them interacting with the atoms, and the "size" of these interactions is related to the reduction in the neutrino flux.

"As a result, current data about solar neutrinos can be used to put limits on the extent of the interactions between dark matter and atoms, and using numerical codes we have proved that certain values correspond to a reduction in the flux of solar neutrinos and clash with the measurements," the scientist reveals.

The team has applied their calculations to better understand the effects of low mass dark matter particles (between 4 and 10 gigaelectronvolts). At this level we find models that attempt to explain the results of experiments such as DAMA (beneath an Italian mountain) or CoGent (in a mine in the USA), which look for dark material using "scintillators" or WIMP detectors.

Debate about WIMP and solar composition

This year another study by scientists from Oxford University (United Kingdom) also appeared. It states that WIMPs not only reduce the fluxes of solar neutrinos, but also, furthermore, modify the structure of the Sun and can explain its composition.

"Our calculations, however, show that the modifications of the star's structure are too small to support this claim and that the WIMPs cannot explain the problem of the composition of the sun," Taoso concludes.

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Galactic Magnifying Lens to Probe Elusive Dark Energy

Galactic Magnifying Lens to Probe Elusive Dark Energy

  10:26:00 AM    Science Lover

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An international team of astronomers using gravitational lensing observations from the NASA/ESA Hubble Space Telescope has taken an important step forward in the quest to solve the riddle of dark energy, a phenomenon which mysteriously appears to power the Universe's accelerating expansion.

This image shows the galaxy cluster Abell 1689, with the 
mass distribution of the gravitational lens overlaid 
(in purple). The mass in this lens is made up partly of normal 
(baryonic) matter and partly of dark matter. Distorted 
galaxies are clearly visible around the edges of the 
gravitational lens. The appearance of these distorted galaxies 
depends on the distribution of matter in the lens and on the 
relative geometry of the lens and the distant galaxies, as well
as on the effect of dark energy on the geometry of the universe. 
(Credit: NASA, ESA, E. Jullo (JPL/LAM), P. 
Natarajan (Yale) and J-P. Kneib (LAM).)

Their results appear in the 20 August 2010 issue of the journal Science.

Normal matter like that found in stars, planets and dust clouds only makes up a tiny fraction of the mass-energy content of the Universe. It is dwarfed by the amount of dark matter -- which is invisible, but can be detected by its gravitational pull. In turn, the amount of dark matter in the Universe is itself overwhelmed by the diffuse dark energy that permeates the entire Universe. Scientists believe that the pressure exerted by this dark energy is what pushes the Universe to expand at an ever-increasing rate.

Probing the nature of dark energy is, therefore, one of the key challenges in modern cosmology. Since its discovery in 1998, the quest has been to characterise and understand it better. This work presents an entirely new way to do so.

Eric Jullo, lead author of a new paper in the journal Science explains: "Dark energy is characterised by the relationship between its pressure and its density: this is known as its equation of state. Our goal was to try to quantify this relationship. It teaches us about the properties of dark energy and how it has affected the development of the Universe."

The team measured the properties of the gravitational lensing in the galaxy cluster Abell 1689. Gravitational lensing is a phenomenon predicted by Einstein's theory of general relativity, and was here used by the team to probe how the cosmological distances (and thus the shape of space-time) are modified by dark energy. At cosmic distances, a huge cluster of galaxies in the foreground has so much mass that its gravitational pull bends beams of light from very distant galaxies, producing distorted images of the faraway objects. The distortion induced by the lens depends in part on the distances to the objects, which have been precisely measured with large ground-based telescopes such as ESO's Very Large Telescope and the Keck Telescopes.

"The precise effects of lensing depend on the mass of the lens, the structure of space-time, and the relative distance between us, the lens and the distant object behind it," explains Priyamvada Natarajan, a co-author of the paper. "It's like a magnifying glass, where the image you get depends on the shape of the lens and how far you hold it from the object you're looking at. If you know the shape of the lens and the image you get, you can work out the path that light followed between the object and your eye."

Looking at the distorted images allows astronomers to reconstruct the path that light from distant galaxies takes to make its long journey to Earth. It also lets them study the effect of dark energy on the geometry of space in the light path from the distant objects to the lensing cluster and then from the cluster to us. As dark energy pushes the Universe to expand ever faster, the precise path that the light beams follow as they travel through space and are bent by the lens is subtly altered. This means that the distorted images from the lens encapsulate information about the underlying cosmology, as well as about the lens itself.

So why is the geometry of the Universe such a big issue?

"The geometry, the content and the fate of the Universe are all intricately linked," says Natarajan. "If you know two, you can deduce the third. We already have a pretty good knowledge of the Universe's mass-energy content, so if we can get a handle on its geometry then we will be able to work out exactly what the fate of the Universe will be."

The real strength of this new result is that it devises a totally new way to extract information about the elusive dark energy. It is a unique and powerful one, and offers great promise for future applications.

According to the scientists, their method required multiple, meticulous steps to develop. They spent several years developing specialised mathematical models and precise maps of the matter -- both dark and "normal" -- that together constitute the Abell 1689 cluster.

Co-author Jean-Paul Kneib explains: "Using our unique method in conjunction with others, we were able to come up with results that were far more precise than any achieved before."

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The international team of astronomers in this study consists of Eric Jullo (Jet Propulsion Laboratory/ Cal Tech, USA and Laboratoire d'Astrophysique de Marseille, France), Priyamvada Natarajan (Yale University, USA), Jean-Paul Kneib (Laboratoire d'Astrophysique de Marseille, France), Anson D'Aloisio (Yale University, USA), Marceau Limousin (Laboratoire d'Astrophysique de Marseille, France and University of Copenhagen, Denmark), Johan Richard (Durham University, UK) and Carlo Schimd (Laboratoire d'Astrophysique de Marseille, France)

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Dark-Matter Search Plunges Physicists to New Depths

Dark-Matter Search Plunges Physicists to New Depths

  2:06:00 AM    Science Lover

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This month physicist Juan Collar and his associates are taking their attempt to unmask the secret identity of dark matter into a Canadian mine more than a mile underground.

Pictured here is the 1-liter bubble chamber during 
testing at MINOS Hall, 350 feet underneath Fermi 
National Accelerator Laboratory. Physicists installed 
a similar but larger bubble chamber for detecting 
dark matter this summer in a laboratory more than 
a mile underground in Sudbury, Canada. 
(Credit: Reidar Hahn/Fermilab)

The team is deploying a 4-kilogram bubble chamber at SNOLab, which is part of the Sudbury Neutrino Observatory in Ontario, Canada. A second 60-kilogram chamber will follow later this year. Scientists anticipate that dark matter particles will leave bubbles in their tracks when passing through the liquid in one of these chambers.

Dark matter accounts for nearly 90 percent of all matter in the universe. Although invisible to telescopes, scientists can observe the gravitational influence that dark matter exerts over galaxies. "There is a lot more mass than literally meets the eye," said Collar, Associate Professor in Physics at the University of Chicago. "When you look at the matter budget of the universe, we have a big void there that we can't explain."

Likely suspects for what constitutes dark matter include Weakly Interacting Massive Particles (WIMPS) and axions. Theorists originally proposed the existence of both these groups of subatomic particles to address issues unrelated to dark matter. "These seem to be perfect to explain all of these observations that give us this evidence for dark matter, and that makes them very appealing," Collar said.

SNOLab will be the most ambitious in a series of underground locations where Collar and his colleagues have searched for dark matter. In 2004, they established the Chicagoland Observatory for Underground Particle Physics (COUPP) at Fermi National Accelerator Laboratory.

"We started with a detector the size of a test tube and now have increased the mass by a factor of more than a thousand," said Fermilab physicist Andrew Sonnenschein. "It's exciting to see the first bubble chamber being sent off to SNOLab, because the low level of interference we can expect from the cosmic rays there will make our search for dark matter enormously more sensitive."

The COUPP collaboration consists of scientists from UChicago, Fermilab and Indiana University at South Bend. In 2008 the collaboration released its first results that established an old technology of particle physics -- the bubble chamber -- as a potential dark-matter detector.

COUPP extends to the city of Chicago's flood-control infrastructure, called the Tunnel and Reservoir Project. The city has granted COUPP scientists access to the tunnels, 330 feet underground, to test prototypes of their instruments. The collaboration also tested instruments in a chamber 350 feet below Fermilab, and in a sub-basement of the Laboratory for Astrophysics and Space Research on the UChicago campus.

Collar continually seeks underground venues for his research in order to screen out false signals from various natural radiation sources, including cosmic rays from deep space. "It's an interesting lifestyle," Collar said.

The troublesome underground radiation sources consist of charged particles that lose energy as they traverse through a mile or more of rock. But rock has no impact on particles that interact weakly with matter, such as WIMPS, thus the move to Sudbury.

"SNOLab is a very special, spectacular place, because the infrastructure that the Canadians have developed down there is nothing short of amazing," Collar said. Even though SNOLab sits atop a working nickel mine, conditions there are pristinely antiseptic.

"As you walk in, you have to shower to remove any trace of dust," he said. "It's a clean-room atmosphere, meaning that there's essentially no specks of dust anywhere. We have to worry about such things, sources of radiation associated with dust."

Collar also is a member of the Coherent Germanium Neutrino Technology (CoGeNT) collaboration, which operates a detector that sits nearly half a mile deep at the Soudan Underground Mine State Park in northern Minnesota. The 60-kilogram detector that Collar and colleagues will install at SNOLab later this year, meanwhile, undergoes testing in a tunnel 350 feet beneath Fermilab.

Linking the two sites is an invisible beam of neutrinos that stretches 450 miles from Fermi to Soudan. The beam is part of the Main Injector Neutrino Oscillation Search (MINOS), a particle-physics experiment that is unrelated to the search for dark matter.

The two detectors rely on entirely different techniques. CoGeNT uses a new type of germanium detector that targets the detection of light WIMPS.

"Most of us have been concentrating on intermediate-mass WIMPS for decades," Collar said. "In the last few years the theoreticians have been telling us more and more, look, under these other sets of assumptions, it could be a lighter WIMP. This device is actually the first of its kind in the sense that it's targeted specifically for light WIMPS. We're seeing interesting things with it that we don't fully understand yet."

Collar estimates that it'll take a decade or more for physicists to become completely convinced that they've seen dark-matter particles.

"It's going to take a lot of information from very many different points of view and entirely independent techniques," he said. "One day we'll figure it out."

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Dark Matter May Be Lurking at Heart of the Sun

Dark Matter May Be Lurking at Heart of the Sun

  4:06:00 PM    Science Lover

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A scientist at Royal Holloway, University of London believes dark matter is lurking at the centre of the sun and cooling down its core temperature.

A full-disk multiwavelength extreme ultraviolet 
image of the sun taken by SDO on March 30, 2010. 
False colors trace different gas temperatures. Reds 
are relatively cool (about 60,000 Kelvin, or 107,
540 F); blues and greens are hotter (greater than 
1 million Kelvin, or 1,799,540 F). (Credit: NASA/
Goddard/SDO AIA Team)

The latest study, led by Dr Stephen West from the Department of Physics at Royal Holloway, looks at the possible effects of dark matter on the properties of the sun, if these elusive particles become trapped at its centre.

"Dark matter makes up more than 80 per cent of the total mass of the universe. We know that dark matter exists but to date it has never been produced in a laboratory or directly observed in any experiment, as a result we have very little information about what it actually is. It is important that we examine all possible ways of probing the nature of dark matter and the sun could provide us with an unexpected laboratory in which to do this," says Dr West.

Dark matter is expected to form a halo around our galaxy and since the sun is in motion around the galaxy it experiences a dark matter "wind" as it moves through this halo. Some of the dark matter particles may collide with the elements in the sun and become gravitationally captured by the sun. This could lead to a build up of dark matter particles at the centre of the sun.

The research team's simulations show that the effect of this build up is to reduce the temperature of the solar core. The dark matter particles can absorb heat at the core and transfer it out towards the surface, decreasing the temperature of the core. This change in temperature affects the number of neutrinos produced as by-products in nuclear reactions within the Sun and it is hoped that by examining these neutrinos we can gain information about the Sun's core temperature and whether dark matter plays an important role in solar physics. This in turn could provide information about the mass of individual dark matter particles and how they interact with the elements in the sun.

Dr West adds, "The next step in the work is to look more closely at the change in the predicted number of neutrinos produced in the sun as a result of dark matter collecting at the core and to examine the sensitivity of existing neutrino experiments to this change. In addition, an investigation of the possibility of probing this type of dark matter at the Large Hadron Collider is planned. The LHC could provide complimentary information about the properties of dark matter which along with the information from the sun may lead to a clearer picture of one of the more puzzling issues in physics."

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Astronomers Confirm Einstein's Theory of Relativity

Astronomers Confirm Einstein's Theory of Relativity

  12:08:00 AM    Science Lover

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A group of astronomers [1], led by Tim Schrabback of the Leiden Observatory, conducted an intensive study of over 446 000 galaxies within the COSMOS field, the result of the largest survey ever conducted with Hubble. In making the COSMOS survey, Hubble photographed 575 slightly overlapping views of the same part of the Universe using the Advanced Camera for Surveys (ACS) onboard Hubble. It took nearly 1000 hours of observations.

This image shows a smoothed reconstruction of the total (mostly dark) matter distribution in the COSMOS field, created from data taken by the NASA/ESA Hubble Space Telescope and ground-based telescopes. It was inferred from the weak gravitational lensing distortions that are imprinted onto the shapes of background galaxies. The color coding indicates the distance of the foreground mass concentrations as gathered from the weak lensing effect. Structures shown in white, cyan and green are typically closer to us than those indicated in orange and red. To improve the resolution of the map, data from galaxies both with and without redshift information were used. The new study presents the most comprehensive analysis of data from the COSMOS survey. The researchers have, for the first time ever, used Hubble and the natural "weak lenses" in space to characterise the accelerated expansion of the universe. (Credit: NASA, ESA, P. Simon (University of Bonn) and T. Schrabback (Leiden Observatory))

In addition to the Hubble data, researchers used redshift [2] data from ground-based telescopes to assign distances to 194 000 of the galaxies surveyed (out to a redshift of 5). "The sheer number of galaxies included in this type of analysis is unprecedented, but more important is the wealth of information we could obtain about the invisible structures in the Universe from this exceptional dataset," says co-author Patrick Simon from Edinburgh University.

In particular, the astronomers could "weigh" the large-scale matter distribution in space over large distances. To do this, they made use of the fact that this information is encoded in the distorted shapes of distant galaxies, a phenomenon referred to as weak gravitational lensing [3]. Using complex algorithms, the team led by Schrabback has improved the standard method and obtained galaxy shape measurements to an unprecedented precision. The results of the study will be published in an upcoming issue of Astronomy and Astrophysics.

The meticulousness and scale of this study enables an independent confirmation that the expansion of the Universe is accelerated by an additional, mysterious component named dark energy. A handful of other such independent confirmations exist. Scientists need to know how the formation of clumps of matter evolved in the history of the Universe to determine how the gravitational force, which holds matter together, and dark energy, which pulls it apart by accelerating the expansion of the Universe, have affected them. "Dark energy affects our measurements for two reasons. First, when it is present, galaxy clusters grow more slowly, and secondly, it changes the way the Universe expands, leading to more distant -- and more efficiently lensed -- galaxies. Our analysis is sensitive to both effects," says co-author Benjamin Joachimi from the University of Bonn. "Our study also provides an additional confirmation for Einstein's theory of general relativity, which predicts how the lensing signal depends on redshift," adds co-investigator Martin Kilbinger from the Institut d'Astrophysique de Paris and the Excellence Cluster Universe.

The large number of galaxies included in this study, along with information on their redshifts is leading to a clearer map of how, exactly, part of the Universe is laid out; it helps us see its galactic inhabitants and how they are distributed. "With more accurate information about the distances to the galaxies, we can measure the distribution of the matter between them and us more accurately," notes co-investigator Jan Hartlap from the University of Bonn. "Before, most of the studies were done in 2D, like taking a chest X-ray. Our study is more like a 3D reconstruction of the skeleton from a CT scan. On top of that, we are able to watch the skeleton of dark matter mature from the Universe's youth to the present," comments William High from Harvard University, another co-author.

The astronomers specifically chose the COSMOS survey because it is thought to be a representative sample of the Universe. With thorough studies such as the one led by Schrabback, astronomers will one day be able to apply their technique to wider areas of the sky, forming a clearer picture of what is truly out there.

Notes:

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

[1] The international team of astronomers in this study was led by Tim Schrabback of the Leiden University. Other collaborators included: J. Hartlap (University of Bonn), B. Joachimi (University of Bonn), M. Kilbinger (IAP), P. Simon (University of Edinburgh), K. Benabed (IAP), M. Bradac (UCDavis), T. Eifler (University of Bonn), T. Erben (University of Bonn), C. Fassnacht (University of California, Davis), F. W. High(Harvard), S. Hilbert (MPA), H. Hildebrandt (Leiden Observatory), H. Hoekstra (Leiden Observatory), K. Kuijken (Leiden Observatory), P. Marshall (KIPAC), Y. Mellier (IAP), E. Morganson (KIPAC), P. Schneider (University of Bonn), E. Semboloni (University of Bonn), L. Van Waerbeke (UBC) and M. Velander (Leiden Observatory).

[2] In astronomy, the redshift denotes the fraction by which the lines in the spectrum of an object are shifted towards longer wavelengths due to the expansion of the Universe. The observed redshift of a remote galaxy provides an estimate of its distance. In this study the researchers used redshift information computed by the COSMOS team (http://ukads.nottingham.ac.uk/abs/2009ApJ...690.1236I) using data from the SUBARU, CFHT, UKIRT, Spitzer, GALEX, NOAO, VLT, and Keck telescopes.

[3] Weak gravitational lensing: The phenomenon of gravitational lensing is the warping of spacetime by the gravitational field of a concentration of matter, such as a galaxy cluster. When light rays from distant background galaxies pass this matter concentration, their path is bent and the galaxy images are distorted. In the case of weak lensing, these distortions are small, and must be measured statistically. This analysis provides a direct estimate for the strength of the gravitational field, and therefore the mass of the matter concentration. When determining precise shapes of galaxies, astronomers have to deal with three main factors: the intrinsic shape of the galaxy (which is unknown), the gravitational lensing effect they want to measure, and systematic effects caused by the telescope and camera, as well as the atmosphere, in case of ground-based observations.

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