Friday 11 October 2013

TIME 05:54

Pulverized Asteroid around Distant Star Was Full of Water

Pulverized Asteroid around Distant Star Was Full of Water

The first discovery of a rocky, watery object beyond our solar system shows how planets might get their oceans

OCEAN BEARER: The oceans on Earth and other rocky planets likely arrived via impacting asteroids and comets. Now, astronomers have spotted the remains of a watery asteroid around a distant star that could represent just such an ocean bearer.Image: Mark A. Garlick, space-art.co.uk, University of Warwick and University of Cambridge

A decimated planetary system around a distant star holds the relics of a giant asteroid that may have once been flooded with water. The finding offers intriguing clues as to how planets become habitable, and may also provide an unsettling peek at what our own solar system might be in for.

This system lies 170 light-years away and is centered on a star, GD 61, that is nearing the end of its life. It is a white dwarf—the dense hulk left over after a star has used up its fuel for nuclear fusion and cast off its outer gaseous layers into space. These stars start out roughly the size of the sun, and end up condensed into a sphere about the size of Earth.

Astronomers did a bit of planetary forensics on GD 61, which is surrounded by rubble—the remains of a large asteroid orbiting the star that seems to have been kicked into a close orbit, where the white dwarf’s strong gravity ripped it to shreds. Some of the asteroid’s remains are now scattered over the surface of the star, where they show up as chemical signatures in the light of thewhite dwarf.

The researchers used the Hubble Space Telescope’s Cosmic Origins Spectrograph to observe GD 61 and split its light into constituent colors, revealing the chemicals it contains. They found magnesium, iron, silicon and other heavy elements, which wouldn’t exist naturally on the surface of a white dwarf, suggesting that they fell onto the star from an orbiting object. The researchers also found a huge excess of oxygen—an amount, they say, that indicates the asteroid polluting the star’s surface was originally composed of 26 percent water. That’s pretty wet—Earth, by contrast, is only 0.02 percent water. “This work marks the first detection of water-rich rocks in exoasteroids, and is an important step in developing a comprehensive picture of exoplanetary systems,” says Kevin France of the University of Colorado at Boulder, who wasn’t involved in the research.

The find could be significant, because theorists think Earth, having formed too close to the sun for water to survive, got its oceans from just such large, wet asteroids that impacted it long ago. “We’ve got the same kind of object which probably delivered Earth’s oceans, and we found this around another star,” says research leader Jay Farihi at the University of Cambridge in England. The discovery, he says, is a step in the quest to find habitable worlds, and maybe even life, beyond Earth. “This goes beyond planets in the habitable zone. We have some actual chemistry that tells you the ingredients for habitable planets were there.”

Some experts aren’t convinced that the oxygen found on the surface of the white dwarf is a clear sign that water existed on an orbiting asteroid, however. “The link of the pollution of a white dwarf to the inventory of water in an earlier planetary system is a very interesting scientific question still under investigation,” says exoplanet researcher Lisa Kaltenegger of Harvard University and the Max Planck Institute for Astronomy in Germany, who was not involved in the research. Claire Moutou, another exoplanet specialist at the Laboratory of Astrophysicsof Marseille in France, agreed. “I find the analysis/conclusions of the paper reasonable, as far as the amount of oxygen available to lie in H2O molecules is concerned. The interpretation of the origin of this water content is more speculative.”

The scientists behind the project, which is detailed in the October 11 issue of Science, say they took pains to verify that the chemicals they see really do prove the destroyed asteroid had water. They observed the star GD 61 in many wavelengths through many telescopes, including NASA’s Spitzer Space Telescope and two instruments on the W. M. Keck Observatory in Hawaii, along with Hubble. “The authors seem to have done a careful job of cataloguing the elements and searching for reasons to explain away the oxygen excess,” says debris disk expert John Debes of the Space Telescope Science Institute in Baltimore. “The detection of hydrogen in addition to the oxygen is a really convincing signature of water.” The finding sheds light on how planets form and evolve, adds Brice-Olivier Demory, an exoplanet researcher at the Massachusetts Institute of Technology who also was not involved in the research. “This is a startling result strengthening the fact that water can be found in a very diverse range of environments.”

And water is just one of the mysteries about this system. Scientists don’t know for sure if GD 61 had, or has, planets, but they say a giant planet most likely pushed the asteroid in toward its doom near the white dwarf. And they can’t tell how big the asteroid was that deposited this detritus on the star—based on the amount of pollution in the white dwarf’s atmosphere, the researchers estimate the asteroid was at least 90 kilometers wide, but could have been much larger. That would put it in a class of objects known as minor planets, similar to Ceres and Vesta in our own solar system, which are also thought to contain large amounts of water stored under their rocky crusts in the form of buried ice.

The planetary graveyard around GD 61 may be a vision of what’s to come for the sun and its planets in the far future. The sun, like 98 percent of the stars in the galaxy, will also become a white dwarf eventually, and its ferocious gravity will probably strip Earth and other inner planets of their heavy elements. It’s not a pretty picture, but, as Farihi says, “we have five billion years to work on that.”

Friday 4 October 2013

TIME 01:51

New Science Cover Photos for Fb

Friday 27 September 2013

TIME 07:44

Wednesday 11 September 2013

TIME 06:59

How to Make an Object Invisible

A new theoretical design using nanowires provides a way to hide devices from visible light.

A hairbrush-shaped device has been theoretically designed that would use bristles made out of nanowires to bend light around it, rendering the object invisible. The researchers who came up with the design say that it’s the first practical design for an “optical cloak” to work in the visible spectrum. They are now working on building an actual device based on their calculations.

Although still only a theoretical design, it is the first to show how a recently discovered cloaking effect could be made to work for all wavelengths of visible light, says Vladimir Shalaev, a professor of electrical and computer engineering at Purdue University, in West Lafayette, IN, who led the research effort.

“It sets out a road map for building these sorts of structures,” says John Pendry, a professor of theoretical physics at Imperial College London, U.K. Besides making it possible to turn things invisible, the work could lead to ways to create heat shields by bending infrared light around objects, he says. Pendry’s initial research led to last year’s creation of the first working cloaking device, which operated in the microwave range. (See “Cloaking Breakthrough.”) This latest work now shows a way to extend this into the visible-light range, says Pendry.

To become invisible, an object must do two things: it has to be able to bend light around itself, so that it casts no shadow, and it must produce no reflection. While naturally occurring materials are unable to do this, a new class of materials called metamaterials is now making it possible. (See “TR10: Invisible Revolution.”)

Bending light around an object requires a material to have a negative refractive index. The refractive index is a property that dictates how light passes through a medium; it’s the reason a stick will look bent when placed in water. If water had a negative refractive index, it would make the stick look as though it were bending back on itself.

Last year, Pendry demonstrated that it is theoretically possible to design structures of very thin conducting wires that could have an effect on the electric and magnetic fields of microwaves, causing them to bend in unnatural ways such as this. This theory was later backed up by experiments carried out by David Smith and David Schurig at Duke University, in Durham, NC.

But repeating the success for visual light seemed to present problems. For one thing, making the design used by Smith and Schurig work for visible light would require components just 40 nanometers in size.

The solution was to design a device with tightly spaced needles of nanowires, 10 nanometers in diameter and 60 nanometers long, emanating from a cylindrical central spoke. In the current issue of the journal Nature Photonics, the researchers show how–in theory at least–this would cloak the object from red light of wavelength 632.8 nanometers long.

There are limitations to this approach, however. A very small percentage of light would still be reflected, so the object would not be entirely invisible. Also, while the design can be adapted to work for other frequencies in the visible range, the design will still only work for a very narrow band of light.

“This is a real problem,” says Ulf Leonhardt, a professor of theoretical physics at St. Andrews University, in Scotland, and an expert in this field. “It would look completely odd, and you would definitely see something.” But he says that this is not an indictment of the Purdue research; rather, it’s a general problem with research into cloaking so far.

“It’s still an important step to go into the visible range,” says Leonhardt. “And it’s a definite step forwards.” But to make things truly disappear before our eyes, a way will need to be found to make devices work across a broad range of frequencies, he says.

Even so, using nanowires is a very practical way forward, says Pendry. “It’s very useful because what we really want now is to see how well people can build them,” he says. Indeed, this is what the group is working on now. “The next step is to fabricate and test an actual sample,” says Alexander Kildishev, a research scientist at Purdue. This work will be carried out in collaboration with Purdue’s Birck Nanotechnology Center.

Friday 6 September 2013

TIME 09:21

Gravitation

Gravitation, or gravity, is a natural phenomenon by which all physical bodies attract each other. It is most commonly experienced as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped.

Gravitation is one of the four fundamental interactions of nature, along with electromagnetism, and the nuclear strong force and weak force. In modernphysics, the phenomenon of gravitation is most accurately described by the general theory of relativity by Einstein, in which the phenomenon itself is a consequence of the curvature of spacetime governing the motion of inertial objects. The simpler Newton's law of universal gravitation postulates the gravity force proportional to masses of interacting bodies and inversely proportional to the square of the distance between them. It provides an accurate approximation for most physical situations including calculations as critical as spacecraft trajectory.

From a cosmological perspective, gravitation causes dispersed matter to coalesce, and coalesced matter to remain intact, thus accounting for the existence of planets, stars, galaxies and most of the macroscopic objects in the universe. It is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth; for the formation of tides; for natural convection, by which fluid flow occurs under the influence of a density gradient and gravity; for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena observed on Earth and throughout the universe.

Scientific revolution

Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and early 17th centuries. In his famous (though possiblyapocryphal experiment dropping balls from the Tower of Pisa, and later with careful measurements of balls rolling down inclines, Galileo showed that gravitation accelerates all objects at the same rate. This was a major departure from Aristotle's belief that heavier objects accelerate faster. Galileo postulated air resistance as the reason that lighter objects may fall slower in an atmosphere. Galileo's work set the stage for the formulation of Newton's theory of gravity.

Newton's theory of gravitation

Sir Issac Newton :-

In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. In his own words, “I deduced that the forces which keep the planets in their orbs must [be] reciprocally as the squares of their distances from the centers about which they revolve: and thereby compared the force requisite to keep the Moon in her Orb with the force of gravity at the surface of the Earth; and found them answer pretty nearly.”

Newton's theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the general position of the planet, and Le Verrier's calculations are what led Johann Gottfried Galle to the discovery of Neptune.

A discrepancy in Mercury's orbit pointed out flaws in Newton's theory. By the end of the 19th century, it was known that its orbit showed slight perturbations that could not be accounted for entirely under Newton's theory, but all searches for another perturbing body (such as a planet orbiting the Sun even closer than Mercury) had been fruitless. The issue was resolved in 1915 by Albert Einstein's new theory of general relativity, which accounted for the small discrepancy in Mercury's orbit.

Although Newton's theory has been superseded, most modern non-relativistic gravitational calculations are still made using Newton's theory because it is a much simpler theory to work with than general relativity, and gives sufficiently accurate results for most applications involving sufficiently small masses, speeds and energies.

TIME 09:13

Gravity!

We've all heard the story. A young Isaac Newton is sitting beneath an apple tree contemplating the mysterious universe. Suddenly - boink! -an apple hits him on the head. "Aha!" he shouts, or perhaps, "Eureka!" In a flash he understands that the very same force that brought the apple crashing toward the ground also keeps the moon falling toward the Earth and the Earth falling toward the sun: gravity.

Or something like that. The apocryphal story is one of the most famous in the history of science and now you can see for yourself what Newton actually said. Squirreled away in the archives of London's Royal Society was a manuscript containing the truth about the apple.

It is the manuscript for what would become a biography of Newton entitled Memoirs of Sir Isaac Newton's Life written by William Stukeley, an archaeologist and one of Newton's first biographers, and published in 1752. Newton told the apple story to Stukeley, who relayed it as such:

"After dinner, the weather being warm, we went into the garden and drank thea, under the shade of some apple trees...he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind. It was occasion'd by the fall of an apple, as he sat in contemplative mood. Why should that apple always descend perpendicularly to the ground, thought he to himself..."

So it turns out the apple story is true - for the most part. The apple may not have hit Newton in the head, but I'll still picture it that way. Meanwhile, three and a half centuries and an Albert Einstein later, physicists still don't really understand gravity. We're gonna need a bigger apple.

Thursday 5 September 2013

TIME 08:40

Quarks

Quarks have various intrinsic properties, including electric charge, color charge, mass, and spin. Quarks are the only elementary particles in theStandard Model of particle physics to experience all four fundamental interactions, also known as fundamental forces (electromagnetism, gravitation,strong interaction, and weak interaction), as well as the only known particles whose electric charges are not integer multiples of the elementary charge. For every quark flavor there is a corresponding type of antiparticle, known as an antiquark, that differs from the quark only in that some of its properties have equal magnitude but opposite sign.

A quark (/ˈkwɔrk/ or /ˈkwɑrk/) is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles calledhadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly observed or found in isolation; they can be found only within hadrons, such as baryons (of which protons and neutrons are examples), and mesons. For this reason, much of what is known about quarks has been drawn from observations of the hadrons themselves.

There are six types of quarks, known as flavors: up, down, strange, charm, bottom, and top. Up and down quarks have the lowest masses of all quarks. The heavier quarks rapidly change into up and down quarks through a process of particle decay: the transformation from a higher mass state to a lower mass state. Because of this, up and down quarks are generally stable and the most common in the universe, whereas strange, charm, top, and bottom quarks can only be produced in high energy collisions (such as those involving cosmic rays and in particle accelerators).

The quark model was independently proposed by physicists Murray Gell-Mann and George Zweig in 1964. Quarks were introduced as parts of an ordering scheme for hadrons, and there was little evidence for their physical existence until deep inelastic scattering experiments at the Stanford Linear Accelerator Center in 1968. All six flavors of quark have since been observed in accelerator experiments; the top quark, first observed atFermilab in 1995, was the last to be discovered.

The Standard Model is the theoretical framework describing all the currently known elementary particles, as well as the Higgs boson.^[8]This model contains six flavors of quarks (q), named up (u), down (d), strange (s), charm (c), bottom (b), and top (t). Antiparticles of quarks are called antiquarks, and are denoted by a bar over the symbol for the corresponding quark, such as u for an up antiquark. As with antimatter in general, antiquarks have the same mass, mean lifetime, and spin as their respective quarks, but the electric charge and other charges have the opposite sign.

Quarks are spin-¹⁄₂ particles, implying that they are fermions according to the spin-statistics theorem. They are subject to the Pauli exclusion principle, which states that no two identical fermions can simultaneously occupy the same quantum state. This is in contrast tobosons (particles with integer spin), any number of which can be in the same state.^[10] Unlike leptons, quarks possess color charge, which causes them to engage in the strong interaction. The resulting attraction between different quarks causes the formation of composite particles known as hadrons (see "Strong interaction and color charge" below).

The quarks which determine the quantum numbers of hadrons are called valence quarks; apart from these, any hadron may contain an indefinite number of virtual (or sea) quarks, antiquarks, and gluons which do not influence its quantum numbers. There are two families of hadrons: baryons, with three valence quarks, and mesons, with a valence quark and an antiquark. The most common baryons are the proton and the neutron, the building blocks of the atomic nucleus. A great number of hadrons are known (see list of baryons andlist of mesons), most of them differentiated by their quark content and the properties these constituent quarks confer. The existence of"exotic" hadrons with more valence quarks, such as tetraquarks (qqqq) and pentaquarks (qqqqq), has been conjectured but not proven.^{[nb 1]}

Elementary fermions are grouped into three generations, each comprising two leptons and two quarks. The first generation includes up and down quarks, the second strange and charm quarks, and the third bottom and top quarks. All searches for a fourth generation of quarks and other elementary fermions have failed, and there is strong indirect evidence that no more than three generations exist.^{[nb 2]}Particles in higher generations generally have greater mass and less stability, causing them to decay into lower-generation particles by means of weak interactions. Only first-generation (up and down) quarks occur commonly in nature. Heavier quarks can only be created in high-energy collisions (such as in those involving cosmic rays), and decay quickly; however, they are thought to have been present during the first fractions of a second after the Big Bang, when the universe was in an extremely hot and dense phase (the quark epoch). Studies of heavier quarks are conducted in artificially created conditions, such as in particle accelerators.

Having electric charge, mass, color charge, and flavor, quarks are the only known elementary particles that engage in all four fundamental interactions of contemporary physics: electromagnetism, gravitation, strong interaction, and weak interaction. Gravitation is too weak to be relevant to individual particle interactions except at extremes of energy (Planck energy) and distance scales (Planck distance). However, since no successful quantum theory of gravity exists, gravitation is not described by the Standard Model.

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