Scientists find answer to supernova riddle

The discovery of a supernova only hours after its explosion has probably solved a long-standing mystery on the origin of the brightest known phenomena in the Universe, scientists reported Wednesday.
On August 24, scientists witnessed the spectacular eruption of light and energy thrown off by the birth of SN 2011fe, the brightest and -- at a mere 20.9 million light years away -- closest-to-Earth supernova in over 25 years.
One light year is the distance that light travels in 365 Earth days, about 9.46 trillion kilometres or 5.87 trillion miles.
"We caught the supernova just 11 hours after it exploded, so soon that we were later able to calculate the actual moment of the explosion within 20 minutes," said Peter Nugent of the US Lawrence Berkeley National Laboratory and lead author of one of two studies, both published in Nature.
"With this close-up look, we found things nobody had dreamed of," he said in a statement.
Brightness thrown off by the violent stellar blast of type 1a supernovas is the yardstick for measuring distances across space.
This was crucial in this year's Nobel Prize winning discovery that the expansion of the Universe is accelerating and not slowing down, as once thought.
Up to now, astronomers had advanced three competing scenarios to explain the origin of 1a supernovas, rare events that only happen once every couple of hundred years in a galaxy such as our own.
In all three, a so-called white dwarf -- an ageing star in decline -- steals matter, and energy, from a companion star until the white dwarf explodes in a flash a billion times brighter than our Sun.
A supernova is so powerful it can outshine an entire galaxy such as the Milky Way, which contains some 200 billion stars, for several weeks.
White dwarfs are essentially Earth-sized diamonds. A single tablespoon weighs about ten tonnes.
Most white dwarfs die not with a bang but a whimper, gradually leaking away heat over billions of years.
But a few interact with other stars to create supernova detonations that are, in essence, colossal thermonuclear explosions.
The question was this: what species are these progenitor companion stars that feed white dwarfs until they burst?
Candidates included a red giant, a second white dwarf, and a so-called subgiant star, of which our Sun is a specimen.
By looking at pre-blast images captured by the Hubble Space Telescope, one team of scientists led by Li Weidong was able to exclude the red giants, which are 10,000 times more luminous that the Sun.
They were not, however, able to narrow things down more.
Nugent's team, which observed SN 2011fe exploding in the Pinwheel Galaxy from the California's Palomar Observatory, took the analysis a step further.
Sifting through the spectrum of the supernova as it expanded, they determined that the companion start was most likely a subgiant, also known as a main-sequence star.
"If there was a giant companion star orbiting nearby, we should have seen some fireworks when the debris from the supernova crashed into it," said co-author Daniel Kasen, a professor at the University of California at Berkeley.
"Because we didn't observe any bright flashes like that, we determined that the companion star could not have been much bigger than our Sun."
"Although the studies do not yet provide a definitive answer to this question, they are a reassuring step forward," said Mario Hamuy, in a commentary, also published in Nature.
But scientists may have to wait another 30 years before another supernova explodes in our neighbourhood or, if we are lucky, in our very own Milky Way, he said.

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Why has Britain done a U-turn on plutonium?

Why does the UK government want to convert its 112 tonnes of plutonium — the largest civilian stockpile in the world — into mixed-oxide fuel (MOX), when just a few months ago it announced the closure of the only MOX production facility in the country because of a lack of demand? Energy minister Charles Hendry announced last week that converting the plutonium to MOX was still the plan, but a new £3-billion (US$4.7-billion) plant would only be built if it could be shown that it was both affordable and offered value for money.

Although at first glance this may seem fiscally prudent, when taken with other recent events it starts to look nonsensical. Just a few weeks ago, the Nuclear Decommissioning Authority (NDA), responding to the government’s own request to consider how to deal with the stockpile, advised that the cost of making MOX is greater than its value as a fuel. And therefore, the most cost-effective plan would be to continue storing the plutonium until a geological disposal facility becomes available for it to be buried underground. So what’s going on? To make sense of it all, Nature peers through the looking glass of the British nuclear industry.

Why would the UK government want to reprocess plutonium into fuel?

Partly, because the plutonium is a huge embarrassment. To continue storing it is not only a constant reminder of how ill-thought-out British nuclear policy has been over the past decades, but it also poses a risk to non-proliferation. So converting it into MOX would transform a huge pile of waste — which the NDA euphemistically calls a “zero value asset” — into something potentially useful, while making the plutonium far harder to weaponize were it to fall into the wrong hands.

So why is it closing the only plant that can do that?Ostensibly, because, in the wake of the Fukushima nuclear disaster, the Sellafield MOX Plant no longer has any customers. But in truth it never really worked. It was built to convert the UK plutonium stockpile into MOX, but, having been plagued by technical failures and delays, it has managed to produce only around 2.5% of its intended quota since it started operating ten years ago. With such a low throughput, it would have been unable to convert the UK stockpile fast enough to provide MOX for new reactors. And so in 2010 the NDA did a deal with ten Japanese utility companies to process their smaller amounts of plutonium and supply them with MOX, a deal that ultimately sank beneath a tsunami.

Why build a new one?

Because the problem hasn’t gone away. Britain still needs to get rid of the plutonium and, despite the failings of the Sellafield plant, MOX production is a proven technology. The one other plant in the world, the Melox plant in Gard, France, has produced around 1,700 tonnes of MOX since it was built in 1995. So, currently, the only other options are to do nothing — keeping the plutonium in storage until geological disposal becomes possible sometime after 2075 — or to process it so that it can supply a fast reactor, such as the kind that, with almost comic timing, GE Hitachi offered to build at Sellafield last week. The problem with this is that, despite 30 years in development, these reactors are still an unproven technology.

Is it worth it?

According to the NDA, not if you care about making a profit. With the low cost of uranium and the high cost of producing MOX, the reprocessed fuel would probably have to be given away. But profit isn’t everything. Indeed, as long-term plutonium managing solutions go, MOX production gets the NDA’s backing. And that is the message Hendry is putting out, that although the government is not quite ready to do anything with the plutonium yet, when it is ready it will be taking the MOX route. And if that means not making a profit, that’s a small price to pay for getting rid of such an albatross. It’s a brave decision, and one that gets the backing of both the Royal Society and the government’s former chief scientific adviser David King at the University of Oxford’s Smith School of Enterprise and the Environment. 

Will it ever actually happen?

Despite all the caveats, we could see a MOX plant approved sooner rather than later. Tied into the decision is a proposal for Britain’s next-generation reactors, which would use MOX as fuel, thereby requiring a MOX plant to be in production before they come online. What remains to be seen, however, is whether a new MOX plant will be able to show that the UK nuclear industry has learnt from the mistakes and failures of the Sellafield plant and to get rid of the plutonium once and for all.

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Walk-Through-Wall Effect Might Be Possible With Humanmade Object, Physicists Predict

Tunnel vision. A superthin sheet of carbon atoms suspended could quantum tunnel between two positions, one slightly bowed and one so bent it contacts the metal plate. An atomic force microscopy image of a graphene membrane (inset) 

If you've ever tried the experiment, you know you can't walk through a wall. But subatomic particles can pull off similar feats through a weird process called quantum tunneling. Now, a team of physicists says that it might just be possible to observe such tunneling with a larger, humanmade object, though others say the proposal faces major challenges.

If successful, the experiment would be a striking advance toward fashioning mechanical systems that behave quantum mechanically. In 2010, physicists took a key first step in that direction by coaxing a tiny object into states of motion that can be described only by quantum mechanics. Tunneling would be an even bigger achievement.

So how does quantum tunneling work? Imagine that an electron, for example, is a marble sitting in one of two depressions separated by a small hill, which represent the effects of a sculpted electric field. To cross the hill from one depression to the other, the marble needs to roll with enough energy. If it has too little energy, then classical physics predicts it can never reach the top of the hill and cross over it.

Tiny particles such as electrons, however, can still make it across even if they don't have enough energy to climb the hill. Quantum physics describes such particles as extended waves of probability—and it turns out that there is a probability that one of them will "tunnel" through the hill and suddenly materialize in the other depression, even though the electron can't occupy the high ground between the two low spots.

It sounds unlikely, but scientists and engineers have amply demonstrated quantum tunneling in semiconductors in which electrons tunnel through nonconducting layers of material. (In fact, some types of magnetic hard drives rely on tunneling for reading out data.) And the Nobel Prize-winning scanning tunneling microscope relies on electrons tunneling through a forbidden no man's land between a tiny fingerlike probe and a conducting surface. Still, no one has ever seen a macroscopic object tunnel through an obstacle.

But Mika Sillanpää and colleagues at Aalto University in Finland say it might be possible to do just that using a tiny widget that resembles a trampoline as they reported 8 November in Physical Review B. Researchers would fashion the micrometer-wide trampoline out of graphene, a superstrong, superflexible sheet of carbon only one atom thick. They would suspend the membrane—small but much larger than the atoms and molecules that are the usual domain of quantum physics—over a metal plate. When experimenters applied an electrical voltage, the membrane would have two stable positions: one in which it bows slightly in the middle and one in which it bends enough to contact the plate below. In the Finnish team's design, the electrical and mechanical forces on the membrane create an energy barrier between these two positions. If researchers could lower the membrane's energy by cooling it to a temperature of less than a thousandth of a degree above absolute zero, then the only way it could get between the two positions is quantum tunneling. The experimenters could then observe the membrane's change of configuration by looking for a change in the system's capacitance, a measure of how well it can store electrical charge. Sillanpää says achieving the low temperatures required may take several years, but the team is moving forward with an experiment.

Quantum tunneling in a mechanical system is "the kind of holy grail that people are looking for now," says physicist Walter Lawrence of Dartmouth College, but the experiment is likely to be difficult. Gil-Ho Lee, a physicist at Pohang University of Science and Technology in South Korea, says the proposed experiment would be an important first step toward demonstrating quantum tunneling. But he cautions that it might not be conclusive because the membrane might perform similar flip-flops when it absorbs a little extra energy in the form of heat. "A more sophisticated test must be done," Lee says. He says that searches for quantum tunneling in electrical systems known as Josephson junctions faced similar issues in the 1980s before experiments eventually confirmed tunneling.

So why can't you use quantum tunneling to walk through a wall? Quantum mechanical calculations show that for something as big as a person, the probability is so small that you could wait until the end of the universe and most likely still not find yourself on the other side.

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The Physics of Wine Swirling

Meet the new flavor of wine: fruity with a hint of fluid dynamics. Oenophiles have long gotten the best out of their reds by giving their glasses a swirl before sipping. A new study has revealed the physics behind that sloshing, showing that three factors may determine whether your merlot arcs smoothly or starts to splash.

Twirling a wineglass gently creates smooth arcs in the liquid that then circle, coating the sides of the glass. The gesture isn't just for appearances, says study co-author Martino Reclari, who studies fluid dynamics at the École Polytechnique Fédérale de Lausanne in Switzerland. Scientists and enthusiasts alike have long known that the swirling motion mixes oxygen into a red, enhancing its flavor.

One evening over their own bottle of wine, Reclari and colleagues decided to tackle the physics of this oenological routine. The team filled up small cylinders in a range of sizes with different volumes of a cheap merlot, then set them spinning. To keep things uniform, the researchers employed gyrating machines, commonly used to mix liquids precisely in biology or chemistry labs. This week, at the annual meeting of the American Physical Society's Division of Fluid Dynamics in Baltimore, Maryland, the group reported a mathematical formula explaining how wine sloshes.

Unlike the flavor of a perfectly aged pinot, Reclari says, the factors at play aren't overly complicated. Three factors seemed to determine whether the team spotted one big wave in the wine or several smaller ripples: the ratio of the level of wine poured in to the diameter of the glass; the ratio of the diameter of the glass to the width of the circular shaking; and the ratio of the forces acting on the wine. Those forces affecting the wine were the centrifugal force pushing the liquid to the outside of the glass and the gravitational force shoving the liquid back down.


By tweaking these factors a notch—for instance, by pouring a bit more wine into a glass or shaking that glass in tighter circles—Reclari and colleagues mastered the art of unusual wine waves. Their creations in the video above included the wine lover's standard, a single, smooth crest, all the way to four miniwaves that built in quick succession. Curiously, however, if the researchers kept all three ratios identical, they began to spot the same waves forming again and again, even in cylinders of very different sizes. "If you have a very small glass or a very big glass and you put in the same parameters, you will have exactly the same shape of the wave," Reclari says.

He and colleagues also landed on another important discovery: how overly enthusiastic wine swirlers manage to splash their drinks, possibly staining their sweaters. Just like an ocean crest, wine waves begin to break, turning frothy, if they're moving too quickly, he says. The breaking acceleration for a merlot is about 40% of the force of gravity, the team concluded, or nearly 4 meters per second. That acceleration, in turn, is dependent on the volume of wine in the glass, the force of shaking, and other factors.

The team's formula is useful for more than just helping a wine taster "impress his friends," Reclari says. When growing bacterial cultures, biologists often mix cells in with nutrients in one big jar, then swirl, much like an aficionado over the latest vintage. That rotation distributes the bacterial food throughout the slurry and also removes excess carbon dioxide. Knowing just how liquids slosh in such jars may help lab technicians optimize their growing methods, he adds.

The team's analysis is "simple" but does "make sense," says Vladimir Ajaev, an applied mathematician at Southern Methodist University in Dallas, Texas. And the study illustrates well how seemingly everyday physics, such as the swirling of a glass of wine, might help scientists and engineers develop better lab tools: "At first it might seem like a matter of curiosity," he says. "But then it turns out there are some specific applications."

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Scientists Narrow Down Dark Matter's Mass

Physicists have set the most precise limit yet on the mass of dark matter, the mysterious and elusive stuff that is thought to make up 98 percent of all matter in the universe and nearly a quarter of its total mass.

The researchers used data from NASA's Fermi Gamma-ray Space Telescope to set parameters on the mass of dark matter particles by calculating the rate at which they appear to collide with their antimatter partners and annihilate each other in galaxies that orbit our own Milky Way.

Savvas Koushiappas, an assistant professor in the department of physics at Brown University, and graduate student Alex Geringer-Sameth found that dark matter particles must have a mass greater than 40 giga-electron volts (GeV) — approximately 42 times the mass of a proton.

"What we find is if a particle's mass is less than 40 GeV, then it cannot be the dark matter particle," Koushiappas said in a statement.

The details of the study will be published in the Dec. 1 issue of the journal Physical Review Letters.

Casting doubt on previous findings

The results throw into question recent findings from underground experiments that reported thepotential detection of dark matter, the researchers said.

These experiments claimed to have found dark matter particles with masses ranging from 7 to 12 GeV, which is significantly less than the limit determined by the new study. [Twisted Physics: 7 Mind-Blowing Findings]

Dark matter is invisible, and scientists have long tried in vain to directly detect the mysterious particles. But since dark matter has mass, its presence is inferred based on the gravitational pull it exerts on regular matter.

But it's more complicated than that. In the 1920s, astronomer Edwin Hubble discovered that the universe is not static, but is expanding. More than 70 years later, observations from the Hubble Space Telescope, which was named for the astronomer, found that the universe was expanding at a much more rapid pace than it was earlier.

Cosmologists think a mysterious force called dark energy is behind this puzzling acceleration. Dark energy, like dark matter, has not been directly detected, but it is thought to be the force pulling the cosmos apart at ever-increasing speeds.

"If, for the sake of argument, a dark matter particle's mass is less than 40 GeV, it means the amount of dark matter in the universe today would be so much that the universe would not be expanding at the accelerated rate we observe," Koushiappas said.

Our complicated universe

Dark energy is thought to make up 73 percent of the total mass and energy in the universe. Dark matter accounts for 23 percent, which leaves only 4 percent of the universe composed of the regular matter that can be seen, such as stars, planets, galaxies and people.

But because neither dark matter nor dark energy has been directly detected, they remain unproven concepts.

In at least one respect, dark matter is thought to behave like normal matter: When a dark matter particle meets its matching antimatter partner, they should destroy each other. Antimatter is a sibling to normal matter; an antimatter partner particle is thought to exist for each matter particle, with the same mass but opposite charge.

Scientists suspect that dark matter is made of particles called WIMPs ("weakly interacting massive particles"). When a WIMP and its anti-particle collide, they should annihilate one another.

To examine the mass of dark matter, Koushiappas and Geringer-Sameth essentially reversed the process of annihilation. The researchers observed seven dwarf galaxies that are thought to be full of dark matter because the motion of the stars within them cannot be fully explained by their mass alone.

Since these dwarf galaxies also contain much less hydrogen gas and other regular matter, they help paint a clearer picture of dark matter and its effects, Koushiappas said.

The physicists worked backward using data from the last three years that was collected by the Fermi telescope, which observes the universe in high-energy gamma-ray light. By measuring the number of light particles, called photons, in the galaxies, the scientists calculated backward to deduce how often particles called quarks are produced, which are products of the WIMP-anti-WIMP annihilation reaction.

This enabled the physicists to establish limits on the mass of dark matter particles and the rate at which they annihilate.

"This is a very exciting time in the dark matter search, because many experimental tools are finally catching up to long-standing theories about what dark matter actually is," Geringer-Sameth said in a statement. "We are starting to really put these theories to the test."

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Is Phobos-Grunt Dead? Troubled Russian Probe Still Unresponsive

The European Space Agency announced today (Dec. 2) that it will stop trying to contact the beleaguered Russian Phobos-Grunt spacecraft, which has been stuck in the wrong orbit for almost a month now.
Russia's Phobos-Grunt probe launched Nov. 8 on a mission to collect and return samples from Mars' moon Phobos. But the spacecraft's thrusters malfunctioned shortly after launch, leaving it stuck in a low orbit around Earth rather than on a course for the Red Planet.
A signal from Phobos-Grunt was picked up last week by a European tracking station located in Australia, and since then, the European Space Agency (ESA) has been helping Russia's Federal Space Agency with efforts to rescue the troubled probe.
However, all subsequent attempts to call Phobos-Grunt have failed to make contact, and ESA announced today that it will cease trying.
"In consultation and agreement with Phobos-Grunt mission managers, ESA engineers will end tracking support today," agency officials said in a statement. "Efforts in the past week to send commands to and receive data from the Russian Mars mission via ESA ground stations have not succeeded; no response has been seen from the satellite." [Photos: Russia's Mars Moon Mission]
The agency had attempted to send instructions to the spacecraft to boost its orbit, but officials reported that these commands went unanswered.
Russian officials were unable to decipher the information that was received from ESA's Australian ground station from the probe. While some data received by a Russian station in Baikonour, Kazakhstan reportedly indicated the spacecraft's radio equipment was operational, efforts to regain contact with Phobos-Grunt have failed.
Ultimately, ESA engineers say they have not completely given up hope for Phobos-Grunt. While the chances to save the marooned spacecraft appear to be dwindling, agency officials maintained their willingness to help if needed.
"ESA teams remain available to assist the Phobos-Grunt mission if indicated by any change in situation," officials said in an update posted on ESA's website.
Yet, time is quickly running out to save the $165 million mission, and Russian officials remain tight-lipped about the status of their rescue efforts. The window of opportunity for the probe to reach the Martian moon has closed already, since the journey requires Earth and Mars to be properly aligned.
If control cannot be regained of the spacecraft, scientists have predicted that Phobos-Grunt could fall back to Earth as a piece of space debris sometime in mid-January.
The ambitious Russian mission was designed to study Phobos and return rocks from the Martian moon to Earth in 2014. Phobos-Grunt is the 19th spacecraft Russia has launched toward Mars since 1960. To date, none has achieved full mission success.

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Two Elements Named: Livermorium and Flerovium

Chemistry's periodic table can now welcome livermorium and flerovium, two newly named elements, which were announced Thursday (Dec. 1) by the International Union of Pure and Applied Chemistry. The new names will undergo a five-month public comment period before the official paperwork gets processed and they show up on the table.
Three other new elements just recently finished this process, filling in the 110, 111 and 112 spots.
All five of these elements are so large and unstable they can be made only in the lab, and they fall apart into other elements very quickly. Not much is known about these elements, since they aren't stable enough to do experiments on and are not found in nature. They are called "super heavy," or Transuranium, elements.
The newly named elements fit in the 114 and 116 spots, down in the lower-right corner of the periodic table, and were officially accepted to the periodic table back in June. They originally were synthesized more than 10 years ago, after which repeat experiments led to their confirmation.
Elements 113, 115, 117 and 118 have also been synthesized at Russia's Joint Institute for Nuclear Research, located in Dubna, Russia (about two hours drive from Moscow), but their creation hasn't been confirmed by the International Union yet. Once they have been confirmed, they will also have to go through the naming and public-commenting periods.
Both livermorium and flerovium were also synthesized at the same Russian lab, where Russian researchers were working with American researchers from the Lawrence Livermore National Laboratory in California.
Element 114, previously known as ununquadium, has been named flerovium (Fl), after the Russian institute's Flerov Laboratory of Nuclear Reactions founder, which similarly is named in honor of Georgiy Flerov (1913-1990), a Russian physicist. Flerov's work and his writings to Joseph Stalin led to the development of the USSR's atomic bomb project.
The researchers got their first glimpse at flerovium after firing calcium ions at a plutonium target.
Element 116, which was temporarily named ununhexium, almost ended up with the name moscovium in honor of the region (called an oblast, similar to a province or state) of Moscow, where the research labs are located. In the end, it seems the American researchers won out and the team settled on the name livermorium (Lv), after the national labs and the city of Livermore in which they are located. Livermorium was first observed in 2000, when the scientists created it by mashing together calcium and curium.
"Proposing these names for the elements honors not only the individual contributions of scientists from these laboratories to the fields of nuclear science, heavy-element research, and super-heavy-element research, but also the phenomenal cooperation and collaboration that has occurred between scientists at these two locations," Bill Goldstein, associate director of Lawrence Livermore National Labs' Physical and Life Sciences Directorate, said in a statement.
The names for the next batch of super-heavy atoms is still up for grabs, perhaps moscovium will make a comeback.

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