Today on New Scientist: 11 January 2013

Largest structure challenges Einstein's smooth cosmos

One-twentieth the diameter of the observable universe, a group of galaxies dents the cherished idea that the cosmos is uniform at large scales

Straitjacket drug halts herpes virus's escape stunt

Herpes infections recur as the virus is adept at evading our defences, but a new drug that suppresses enzymes exploited by the virus seems effective

Zoologger: Mouse eats scorpions and howls at the moon

Super-aggressive grasshopper mice are not put off by the deadly venom of the scorpions they feast on - in fact, nothing much seems to scare them

Sand tsunami pictured striking Australian coast

The spectacular wall of sand and dust appears to block out the sun like a giant wave

Astrophile: Zombie stars feed on Earth-like exoplanets

We can now learn what planets around other stars are made of - by looking at the atmospheres of white dwarfs that have swallowed up their worlds

Life will find a way, even in the midst of a hurricane

Not for the faint-hearted: to sample the microbiome of a hurricane, fly a jetliner through it

Physics not biology may be key to beating cancer

Billions of dollars spent on cancer research have yielded no great breakthrough yet. There are other ways to attack the problem, says physicist Paul Davies

Feedback: Return of nominative determinism

The last nominative determinism stories, salads of gizzards and his chestnuts, Australian graduates in outer space, and more

A comeback for virtual reality? Inside the Oculus Rift

The Oculus Rift promises an immersive gaming experience like no other. Niall Firth gets his head in the game and gives it a try

Is the US facing Flu-maggedon?

The US flu season has come early this winter, leaving many hospitals overwhelmed. But is the situation really any worse than usual?

Your body's insights into life and cosmos

The Universe Within by Neil Shubin tells stories from your body about our species, planet and universe. PLUS: a cautionary tale of inspirational scientists

Hands on with Leap Motion's gestural interface

The makers of the ultra-precise gestural interface talk big about killing off the mouse. But it looks like more than just bluster

Personal assistant for your emails streamlines your life

GmailValet aims to use crowdsourcing to give everyone a personal assistant to help deal with their emails - it could cost as little as $2 a day

DNA 'identichip' gives a detailed picture of a suspect

A new microchip-based DNA tester can identify multiple traits of an individual at a time, even where their DNA is scarce

Most fundamental clock ever could redefine kilogram

Physicists have created the first clock with a tick that depends on the hyper-regular frequency of matter itself

Nanomachine mimics nature's protein factory

An artificial ribosome that assembles proteins and peptides could make it much easier to manufacture antibiotics and exotic new materials

Muscle mimic pulls electricity from wet surface

A plastic film that repeatedly curls up and flips over when wet could power devices in remote areas or sensors embedded in sweaty clothing

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Czechs elect president in break with eurosceptic past

PRAGUE: Czechs head to the ballot box for a second day of voting Saturday, with a field of Europe-friendly candidates including an artist tattooed head-to-toe, vying to take over after a decade under eurosceptic Vaclav Klaus.

While former prime ministers Milos Zeman and Jan Fischer, both ex-communists, are tipped as favourites, media pundits said Foreign Minister Karel Schwarzenberg might capitalise on a last-minute charm offensive.

First-round voting in the Czech Republic's first-ever direct presidential election continues on Saturday until 1300 GMT.

None of the nine contenders is likely to clinch a first-round victory, so a runoff between the two top finishers is expected on January 25-26.

With the powers of the Czech president being relatively limited, issues related to the republic's role within the European Union and corruption woes are key in the election.

Both the straight-talking veteran left-winger Zeman and the mild-mannered centre-right statistician Fischer have a far more friendly approach towards the 27-nation bloc than Klaus. Their line echoes the attitude of Klaus's predecessor, the late Velvet Revolution icon Vaclav Havel.

"The Czech Republic should take steps towards more solid EU structures including a single European economic policy," Zeman said in a recent interview, endorsing what Klaus has long described as a nightmare.

As prime minister in 1998-2002, Zeman was responsible for negotiating the 2004 EU entry of his 10.5 million-strong ex-communist country.

Despite Zeman's leftist and pro-European stance, right-winger Klaus -- who wastes no opportunity to slam the EU -- has nevertheless suggested he would vote for him.

"My point is to have a president who has done something for this country and whose experience we can all see," Klaus said after casting his ballot in Prague on Friday. His second and final five-year term ends on March 7.

The centre-right Fischer who served as premier in 2009-2010, has meanwhile insisted that the Czech Republic should be "active in the debate on the EU's future."

All the candidates cast their ballots on Friday.

"I guess you wouldn't expect me to vote for someone else," Fischer conceded to reporters after voting.

"He's a serious man who's in the know, he's no fool," pensioner Udo Cerny told AFP after voting for him in Cernosice, a small town near Prague.

Pipe-smoking 75-year-old Karel Schwarzenberg, an aristocrat bearing the full name of Karl Johannes Nepomuk Josef Norbert Friedrich Antonius Wratislaw Mena Furst zu Schwarzenberg, has also been wooing voters. Many of them perceive him as honest and experienced.

"I feel he would be the least likely to steal," Prague senior citizen Alena Zurkova told AFP, referring to the chronic levels of corruption in Czech politics.

"He is the least corrupt and the most experienced when it comes to diplomacy and international contacts," said Alena Poulova, a young IT expert voting in Cernosice.

The most colourful candidate -- in all senses -- is Vladimir Franz, a 53-year-old drama teacher, classical composer and visual artist tattooed from his head to his feet.

"I think a bit of pure heart would do no harm in politics," Franz, told AFP ahead of the vote. A self-described citizens' candidate with no political experience, he named education, tolerance and culture as his priorities.

Three women and two senators are also in the running.

The election is the first direct presidential vote in the central European nation.

In February 2012, lawmakers approved a switch to popular universal suffrage used in many EU countries to boost the legitimacy of the office. Klaus's re-election in 2008 by parliament was widely perceived as political horse-trading.

The Czech Republic, a NATO and EU member yet to join the eurozone, has been mired in recession for a year, with its central bank predicting moderate 0.2-percent economic growth in 2013. Joblessness stood at 9.4 percent in December.

- AFP/al

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U.S. tells computer users to disable Java software

Updated 9:00 p.m. ET

WASHINGTON The U.S. Department of Homeland Security is advising people to temporarily disable the Java software on their computers to avoid potential hacking attacks.

The recommendation came in an advisory issued late Thursday, following up on concerns raised by computer security experts.

Experts believe hackers have found a flaw in Java's coding that creates an opening for criminal activity and other high-tech mischief.

CNET's Topher Kessler writes:

"The malware has currently been seen attacking Windows, Linux and Unix systems, and while so far has not focused on OS X, may be able to do so given OS X is largely similar to Unix and Java is cross-platform.

Even though the exploit has not been seen in OS X, Apple has taken steps to block it by issuing an update to its built-in XProtect system to block the current version of the Java 7 runtime and require users install an as of yet unreleased version of the Java runtime.

Luckily with the latest versions of Java, users who need to keep it active can change a couple of settings to help secure their systems. Go to the Java Control Panel that is installed along with the runtime, and in the Security section uncheck the option to "Enable Java content in the browser," which will disable the browser plug-in. This will prevent the inadvertent execution of exploits that may be stumbled upon when browsing the Web, and is a recommended setting for most people to do. If you need to see a Java applet on the Web, then you can always temporarily re-enable the plug-in.

The second setting is to increase the security level of the Java runtime, which can also be done in the same Security section of the Java Control Panel. The default security level is Medium, but you can increase this to High or Very High. At the High level, Java will prompt you for approval before running any unsigned Java code, and at the Very High level all Java code will require such approval, regardless of whether or not it is signed."

Java is a widely used technical language that allows computer programmers to write a wide variety of Internet applications and other software programs that can run on just about any computer's operating system.

Oracle Corp. bought Java as part of a $7.3 billion acquisition of the software's creator, Sun Microsystems, in 2010.

Oracle, which is based in Redwood Shores, Calif., had no immediate comment late Friday.

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CDC: Flu Outbreak Could Be Waning

The flu season appears to be waning in some parts of the country, but that doesn't mean it won't make a comeback in the next few weeks, according to the Centers for Disease Control and Prevention.

Five fewer states reported high flu activity levels in the first week of January than the 29 that reported high activity levels in the last week of December, according to the CDC's weekly flu report. This week, 24 states reported high illness levels, 16 reported moderate levels, five reported low levels and one reported minimal levels, suggesting that the flu season peaked in the last week of December.

"It may be decreasing in some areas, but that's hard to predict," CDC Director Dr. Thomas Frieden said in a Friday morning teleconference. "Trends only in the next week or two will show whether we have in fact crossed the peak."

The flu season usually peaks in February or March, not December, said Dr. Jon Abramson, who specializes in pediatric infectious diseases at Wake Forest Baptist Health in North Carolina. He said the season started early with a dominant H3N2 strain, which was last seen a decade ago, in 2002-03. That year, the flu season also ended early.

Click here to see how this flu season stacks up against other years.

Cheryl Evans/The Arizona Republic/AP Photo

Increasing Flu Cases: Best Measures to Ensure Your Family's Health Watch Video

Because of the holiday season, Frieden said the data may have been skewed.

For instance, Connecticut appeared to be having a lighter flu season than other northeastern states at the end of December, but the state said it could have been a result of college winter break. College student health centers account for a large percentage of flu reports in Connecticut, but they've been closed since the fall semester ended, said William Gerrish, a spokesman for the state's department of public health.

The flu season arrived about a month early this year in parts of the South and the East, but it may only just be starting to take hold of states in the West, Frieden said. California is still showing "minimal" flu on the CDC's map, but that doesn't mean it will stay that way.

Click here to read about how flu has little to do with cold weather.

"It's not surprising. Influenza ebbs and flows during the flu season," Frieden said. "The only thing predictable about the flu is that it is unpredictable."

Dr. William Schaffner, chair of preventive medicine at Vanderbilt University Medical Center in Nashville, Tenn., said he was expecting California's seeming good luck with the flu to be over this week.

"Flu is fickle, we say," Schaffner said. "Influenza can be spotty. It can be more severe in one community than another for reasons incompletely understood."

Early CDC estimates indicate that this year's flu vaccine is 62 percent effective, meaning people who have been vaccinated are 62 percent less likely to need to see a doctor for flu treatment, Frieden said.

Although the shot has been generally believed to be more effective for children than adults, there's not enough data this year to draw conclusions yet.

"The flu vaccine is far from perfect, but it's still by far the best tool we have to prevent flu," Frieden said, adding that most of the 130 million vaccine doses have already been administered. "We're hearing of shortages of the vaccine, so if you haven't been vaccinated and want to be, it's better late than never."

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Muscle mimic pulls electricity from wet surface

Electricity has been squeezed from a damp surface for the first time, thanks to a polymer film that curls up and moves – a bit like an artificial muscle – when exposed to moisture. The film could be used to run small, wearable devices on nothing but sweat, or in remote locations where conventional electricity sources aren't available.

When a dry polymer absorbs water, its molecular structure changes. This can, in principle, be converted into larger-scale movement, and in turn electricity. But previous attempts at creating a material powered by a moisture gradient – the difference in chemical potential energy between a wet region and a dry region - failed to produce a useful level of force.

These unsuccessful tries used a polymer called polypyrrole. Now Robert Langer and colleagues at the Massachusetts Institute of Technology have turned to the material again, embedding chains of it within another material, polyol-borate. This more complex arrangement mimics structures found in muscles as well as in plant tissues that bend in response to changes in humidity.

Flipping film

The result looks like an ordinary piece of thin black plastic, but when placed on a wet surface, something extraordinary happens. As the material absorbs water, its end curls away from the surface and the film becomes unstable, so it flips over. The ends have now dried out, so they are ready to absorb more water, and the whole process repeats itself. This continuous flipping motion lets the film travel across a suitably moist surface unaided.

Langer found that a 0.03-millimetre-thick strip, weighing roughly 25 milligrams, could curl up and lift a load 380 times its mass to a height of 2 millimetres. It was also able to move sideways when carrying a load about 10 times its mass.

To extract energy from this effect, Langer's team added a layer of piezoelectric material – one which produces electricity when squeezed. When this enhanced film, weighing about 100 milligrams, flipped over, it generated an output of 5.6 nanowatts – enough to power a microchip in sleep mode.

Electricity from sweat

Though the output is small, it is proof that electricity can be extracted from a water gradient. "To the extent of our knowledge, we are the first to utilise a water gradient, without a pressure gradient, to generate electricity," says Langer.

Large-scale energy harvesting is unlikely as the size of the device needed would be impractical, but it could be used to power small devices such as environmental monitoring systems in remote locations. "It will be interesting for applications where the amount of energy needed may be low but where access to energy may be difficult," says Peter Fratzl at the Max-Planck Institute of Colloids and Interfaces in Potsdam, Germany, who was not involved in the work.

Another application, Langer suggests, would be to place the film inside the clothing of joggers or athletes. The evaporation of sweat could generate enough electricity to power sensors monitoring blood pressure and heart rate.

Journal reference: Science, DOI 10.1126/science.1230262

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Beheading exposes exploitation

(File photo) Sri Lankan women protest outside the Saudi Arabia embassy in Colombo on November 9, 2010.

STORY HIGHLIGHTS

• Saudi authorities beheaded Rizana Nafeek, a Sri Lankan woman


• She was convicted of killing a baby of the family employing her as a housemaid


• This was despite Nafeek's claims that the baby died in a choking accident


• Becker says her fate "should spotlight the precarious existence of domestic workers"

Jo Becker is the Children's Rights Advocacy Director for Human Rights Watch and author of 'Campaigning for Justice: Human Rights Advocacy in Practice.' Follow Jo Becker on Twitter.

(CNN) -- Rizana Nafeek was a child herself -- 17 years old, according to her birth certificate -- when a four-month-old baby died in her care in Saudi Arabia. She had migrated from Sri Lanka only weeks earlier to be a domestic worker for a Saudi family.

Although Rizana said the baby died in a choking accident, Saudi courts convicted her of murder and sentenced her to death. On Wednesday, the Saudi government carried out the sentence in a gruesome fashion, by beheading Rizana.

Jo Becker

Read more: Outrage over beheading of Sri Lankan woman by Saudi Arabia

Rizana's case was rife with problems from the beginning. A recruitment agency in Sri Lanka knew she was legally too young to migrate, but she had falsified papers to say she was 23. After the baby died, Rizana gave a confession that she said was made under duress -- she later retracted it. She had no lawyer to defend her until after she was sentenced to death and no competent interpreter during her trial. Her sentence violated international law, which prohibits the death penalty for crimes committed before age 18.

Rizana's fate should arouse international outrage. But it should also spotlight the precarious existence of other domestic workers. At least 1.5 million work in Saudi Arabia alone and more than 50 million -- mainly women and girls -- are employed worldwide according to the International Labour Organization (ILO).

Read more: Indonesian maid escapes execution in Saudi Arabia

Again according to the ILO, the number of domestic workers worldwide has grown by more than 50% since the mid-1990s. Many, like Rizana, seek employment in foreign countries where they may be unfamiliar with the language and legal system and have few rights.

When Rizana traveled to Saudi Arabia, for example, she may not have known that many Saudi employers confiscate domestic workers' passports and confine them inside their home, cutting them off from the outside world and sources of help.

It is unlikely that anyone ever told her about Saudi Arabia's flawed criminal justice system or that while many domestic workers find kind employers who treat them well, others are forced to work for months or even years without pay and subjected to physical or sexual abuse.

Passport photo of Rizana Nafeek

Read more: Saudi woman beheaded for 'witchcraft and sorcery'

Conditions for migrant domestic workers in Saudi Arabia are among some of the worst, but domestic workers in other countries rarely enjoy the same rights as other workers. In a new report this week, the International Labour Organization says that nearly 30% of the world's domestic workers are completely excluded from national labor laws. They typically earn only 40% of the average wage of other workers. Forty-five percent aren't even entitled by law to a weekly day off.

Last year, I interviewed young girls in Morocco who worked 12 hours a day, 7 days a week for a fraction of the minimum wage. One girl began working at age 12 and told me: "I don't mind working, but to be beaten and not to have enough food, this is the hardest part."

Many governments have finally begun to recognize the risks and exploitation domestic workers face. During 2012, dozens of countries took action to strengthen protections for domestic workers. Thailand, and Singapore approved measures to give domestic workers a weekly day off, while Venezuela and the Philippines adopted broad laws for domestic workers ensuring a minimum wage, paid holidays, and limits to their working hours. Brazil is amending its constitution to state that domestic workers have all the same rights as other workers. Bahrain codified access to mediation of labor disputes.

Read more: Convicted killer beheaded, put on display in Saudi Arabia

Perhaps most significantly, eight countries acted in 2012 to ratify -- and therefore be legally bound by -- the Domestic Workers Convention, with more poised to follow suit this year. The convention is a groundbreaking treaty adopted in 2011 to guarantee domestic workers the same protections available to other workers, including weekly days off, effective complaints procedures and protection from violence.

The Convention also has specific protections for domestic workers under the age of 18 and provisions for regulating and monitoring recruitment agencies. All governments should ratify the convention.

Many reforms are needed to prevent another tragic case like that of Rizana Nafeek. The obvious one is for Saudi Arabia to stop its use of the death penalty and end its outlier status as one of only three countries worldwide to execute people for crimes committed while a child.

Labor reforms are also critically important. They may have prevented the recruitment of a 17 year old for migration abroad in the first place. And they can protect millions of other domestic workers who labor with precariously few guarantees for their safety and rights.

Read more: Malala, others on front lines in fight for women

The opinions expressed in this commentary are solely those of Jo Becker.

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Sheriff: Calif. teen planned attack on classmates

Updated at 9:40 p.m. ET

TAFT, Calif. A 16-year-old student armed with a shotgun walked into a rural California high school on Thursday, shot one student and fired at others and missed before a teacher and another staff member talked him into surrendering, officials said.

The teen victim was in critical but stable condition, and the suspect, whose pockets were stuffed with ammunition, was still being interrogated, Kern County Sheriff Donny Youngblood said at a news conference Thursday evening.

The suspect used a shotgun that belonged to his brother and went to bed Wednesday night with a plan to shoot two fellow students, Youngblood said.

Surveillance video shows the alleged shooter trying to conceal the gun as he nervously entered Taft Union High School through a side entrance after school had started Thursday morning.

When the shots were fired, teacher Ryan Heber tried to get the more than two dozen students out a back door and engaged the shooter in conversation to distract him, Youngblood said. Campus supervisor Kim Lee Fields responded to a call of shots fired and also began talking to the teen.

"They talked him into putting that shotgun down. He in fact told the teacher, `I don't want to shoot you,' and named the person that he wanted to shoot," Youngblood said.

"The heroics of these two people goes without saying. ... They could have just as easily ... tried to get out of the classroom and left students, and they didn't," the sheriff said. "They knew not to let him leave the classroom with that shotgun."

The shooter didn't show up for first period, then interrupted the class of 28 students.

Youngblood said the suspect alleges the two students he targeted had bullied him for more than a year, but the sheriff couldn't confirm the allegations.

"Certainly he believed that the two people he targeted had bullied him, in his mind. Whether that occurred or not we don't know yet," Youngblood said.

Youngblood did not release the student's disciplinary record, saying he didn't have it.

The shotgun is believed to belong to the boy's brother and was in the boy's home, Youngblood said.

The Sheriff's Department did not release the boy's name because he was a juvenile and had yet to be charged. But many students and community members said they knew the boy and said he was often teased, including Alex Patterson, 18, who went to Taft with the suspect before graduating last year.

"He comes off as the kind of kid who would do something like this," Patterson said. "He talked about it a lot, but nobody thought he would."

Trish Montes, who lived next door to the suspect, said he was "a short guy" and "small" who was teased about his stature by many, including the victim.

"Maybe people will learn not to bully people," Montes said. "I hate to be crappy about it, but that kid was bullying him."

Montes said her son had worked at the school and tutored the boy last year, sometimes walking with him between classes because he felt sorry for him.

"All I ever heard about him was good things from my son," Montes said. "He wasn't Mr. Popularity, but he was a smart kid. It's a shame. My kid said he was like a genius. It's a shame because he could have made something of himself."

The wounded student was flown to a hospital in Bakersfield and was listed in stable but critical condition Thursday evening. Officials said a female student was hospitalized with possible hearing damage because the shotgun was fired close to her ear, and another girl suffered minor injuries during the scramble to flee when she fell over a table.

Officials said there's usually an armed officer on campus, but the person wasn't there because he was snowed in. Taft police officers arrived within 60 seconds of first reports.

Bakersfield television station KERO reported receiving phone calls from people inside the school who hid in closets. About 900 students are enrolled at the high school, which includes ninth through 12th grades.

Wilhelmina Reum, whose daughter Alexis Singleton is a fourth-grader at a nearby elementary school, got word of the attack while she was about 35 miles away in Bakersfield and immediately sped back to Taft.

"I just kept thinking this can't be happening in my little town," she told The Associated Press.

"I was afraid I was going to get hurt," Alexis said. "I just wanted my mom to get here so I could go home."

Taft is a community of fewer than 10,000 people amid oil and natural gas production fields about 120 miles northwest of Los Angeles.

The attack there came less than a month after a gunman massacred 20 children and six women at Sandy Hook Elementary School in Newtown, Conn., then killed himself.

That shooting prompted President Barack Obama to promise new efforts to curb gun violence. Vice President Joe Biden, who was placed in charge of the initiative, said he would deliver new policy proposals to the president by next week.

Sen. Dianne Feinstein, D-Calif., said in a statement that her father had attended Taft Union and she has visited the school over the years.

"At this moment my thoughts and prayers are with the victims, and I wish them a speedy recovery," Feinstein said. "But how many more shootings must there be in America before we come to the realization that guns and grievances do not belong together?"

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Judge: Holmes Can Face Trial for Aurora Shooting

Jan 10, 2013 8:45pm

(Arapahoe County Sheriff/AP Photo)

In a ruling that comes as little surprise, the judge overseeing the Aurora, Colo., theater massacre has ordered that there is enough evidence against James Holmes to proceed to a trial.

In an order posted late Thursday, Judge William Sylvester wrote that “the People have carried their burden of proof and have established that there is probable cause to believe that Defendant committed the crimes charged.”

The ruling came after a three-day preliminary hearing this week that revealed new details about how Holmes allegedly planned for and carried out the movie theater shooting, including how investigators say he amassed an arsenal of guns and ammunition, how he booby-trapped his apartment to explode, and his bizarre behavior after his arrest.

PHOTOS: Colorado ‘Dark Knight Rises’ Theater Shooting

Holmes is charged with 166 counts, including murder, attempted murder and other charges related to the July 20 shooting that left 12 people dead and 58 wounded by gunfire. An additional 12 people suffered non-gunshot injuries.

One of the next legal steps is an arraignment, at which Holmes will enter a plea. The arraignment was originally expected to take place Friday morning.

Judge Sylvester indicated through a court spokesman that he would allow television and still cameras into the courtroom, providing the outside world the first images of Holmes since a July 23 hearing. Plans for cameras in court, however, were put on hold Thursday afternoon.

“The defense has notified the district attorney that it is not prepared to proceed to arraignment in this case by Friday,” wrote public defenders Daniel King, Tamara Brady and Kristen Nelson Thursday afternoon in a document objecting to cameras in court.

A hearing in the case will still take place Friday morning. In his order, Judge Sylvester said it should technically be considered an arraignment, but noted the defense has requested a continuance.  Legal experts expect the judge will grant the continuance, delaying the arraignment and keeping cameras out of court for now.

Sylvester also ordered that Holmes be held without bail.

Holmes’ attorneys have said in court that the former University of Colorado neuroscience student is mentally ill. The district attorney overseeing the case has not yet announced whether Holmes, now 25, can face the death penalty.

SHOWS: World News

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Hints of new dark force seen in galactic smash-ups

Colliding clusters of galaxies may hold clues to a mysterious dark force at work in the universe. This force would act only on invisible dark matter, the enigmatic stuff that makes up 86 per cent of the mass in the universe.

Dark matter famously refuses to interact with ordinary matter except via gravity, so theorists had assumed that its particles would be just as aloof with each other. But new observations suggest that dark matter interacts significantly with itself, while leaving regular matter out of the conversation.

"There could be a whole class of dark particles that don't interact with normal matter but do interact with themselves," says James Bullock of the University of California, Irvine. "Dark matter could be doing all sorts of interesting things, and we'd never know."

Some of the best evidence for dark matter's existence came from the Bullet cluster, a smash-up in which a small galaxy cluster plunged through a larger one about 100 million years ago. Separated by hundreds of light years, the individual galaxies sailed right past each other, and the two clusters parted ways. But intergalactic gas collided and pooled on the trailing ends of each cluster.

Mass maps of the Bullet cluster showed that dark matter stayed in line with the galaxies instead of pooling with the gas, proving that it can separate from ordinary matter. This also hinted that dark matter wasn't interacting with itself, and was affected by gravity alone.

Musket shot

Last year William Dawson of the University of California, Davis and colleagues found an older set of clusters seen about 700 million years after their collision. Nicknamed the Musket Ball cluster, this smash-up told a different tale. When Dawson's team analysed the concentration of matter in the Musket Ball, they found that galaxies are separated from dark matter by about 19,000 light years.

"The galaxies outrun the dark matter. That's what creates the offset," Dawson said. "This is fitting that picture of self-interacting dark matter." If dark matter particles do interact, perhaps via a dark force, they would slow down like the gas.

This new picture could solve some outstanding mysteries in cosmology, Dawson said this week during a meeting of the American Astronomical Society in Long Beach, California. Non-interacting dark matter should sink to the cores of star clusters and dwarf galaxies, but observations show that it is more evenly distributed. If it interacts with itself, it could puff up and spread outward like a gas.

So why doesn't the Bullet cluster show the same separation between dark matter and galaxies? Dawson thinks it's a question of age – dark matter in the younger Bullet simply hasn't had time to separate.

New window

The idea complements a previous study that saw evidence for dark forces at work in the Bullet cluster. In 2007 Glennys Farrar of New York University and colleagues said that the smaller cluster was moving too fast for gravity alone to be responsible. They suggested that some mysterious force related to dark matter might be hurrying it along.

Still, two clusters is not a lot to go on. Dawson, Bullock and colleagues are following up with about 20 more galactic collisions to see if they show any unusual behaviours. "I really think that we're almost to the point where we have enough observational data in hand," Dawson said. "We could close the book on self-interacting dark matter."

If the new force does exist, we might soon be able to see its effects on things influenced by dark matter, such as the behavior of black holes or the masses of the first stars, says Douglas Finkbeiner of Harvard University in Cambridge, Massachusetts, who was not involved in the new study.

"The simple thing isn't always the right thing, so I really appreciate that Will is trying to look into these other possibilities," he says.

Louis Strigari of Stanford University in California agrees. "Self-interacting dark matter is worth pursuing because we're still very ignorant," he said. "We're desperate to understand what dark matter is, so any new window is welcome."

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.

All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.

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Israeli, US defence chiefs discuss Middle East issues

WASHINGTON: US Defence Secretary Leon Panetta and his Israeli counterpart Ehud Barak met to underscore a "strong US commitment to Israel's security", the Pentagon said.

US Defence Department spokesman George Little said in a statement that the two men "discussed a range of issues, and expressed their commitment to ensuring continued cooperation on many important regional issues -- particularly Syria, Iran, and Gaza".

"The secretary commended Minister Barak on his tireless efforts in advancing the US-Israel strategic relationship," Little said, adding the pair "reiterated the strong US commitment to Israel's security and the strong US-Israel defence relationship."

The meeting was the 11th for Barak and Panetta, who is leaving his post shortly.

President Barack Obama has nominated former US senator Chuck Hagel to succeed Panetta, a longtime Washington figure who has said he will be leaving public life.

- AFP/al

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