Gravitational lensing image of galaxies (yellow to red) and haloes from clumped dark matter (blue). (Hubble and Yale University)

But recent observations show that these flares fire roughly every 20 minutes – a regularity that is hard to explain in terms of the behaviour of a black hole.

Now Anatoly Svidzinsky, a physicist at Texas A&M University in College Station, Texas, thinks that hypothetical particles called axions could solve the mystery.

Axions have very little mass and no electric charge, and they barely interact with other particles. They were originally proposed to fix a problem with the strong force in particle physics, but have more recently been considered as possible candidates for dark matter, the unseen stuff thought to make up nearly 90 per cent of a galaxy's mass.

In the 1990s, computer simulations of clouds of dark matter made of axions showed that giant bubbles of these particles would burst out from the clouds. Svidzinsky thinks that such bubbles exist at the centre of galaxies.

His model shows that the axion bubbles would expand and contract with a period of 20 minutes – matching the period of infrared and X-ray flares from Sagittarius A*, the location of the supermassive compact object at the centre of our galaxy.

Percentages of dark energy, dark matter and normal matter in the universe. (NASA)

The model predicts that stable axion bubbles would weigh between about 1 million and 2.5 billion times the mass of the sun – exactly the mass range observed for compact objects at the centres of galaxies.

"The proposal looks quite intriguing," says Tim Sumner, who is leading the search for galactic dark matter, including axions, at Imperial College London in the UK. "But it obviously needs a lot more evidence and assessment before it can really displace the more established scenarios."

One big assumption in Svidzinsky's model is that gravity starts to repel as the gravitational field gets stronger – a tweak to general relativity proposed by physicist Huseyin Yilmaz in the 1990s. And this is what causes the bubbles to oscillate. As the bubble grows, its surface tension pulls it back. As it collapses, its gravity eventually becomes repulsive and the bubble expands again.

The fact that Svidzinsky's model relies on this controversial version of gravity doesn't necessarily count against it, says Konstantin Zioutas of the particle physics laboratory CERN in Geneva, Switzerland.

Earth's sun is about half the distance from the center to the edge of the Milky Way galaxy.

"There are various studies in progress around the world which suggest that Einstein did not speak the last word on gravity," says Zioutas. For example, extra dimensions can change the way that gravity behaves in extreme cases.

The other important question is whether axions really exist. There have been attempts to create them in the lab (New Scientist, 14 July, p 35) and even a possible indirect sighting in the sun's halo by Zioutas (New Scientist, 17 April 2004, p 8).

"Until their existence is confirmed, axions will appear to be a deus ex machina," says Zioutas.

Still, Zioutas adds, if Svidzinsky is correct, his idea could solve another mystery perplexing astronomers. As well as X-ray flares, astronomers can see diffuse X-rays emanating from our galactic centre.

"We don't know what can be causing these," says Zioutas. "Any gas that would be hot enough to emit this radiation would be moving too fast to be held in our galaxy."

Dark matter axions, however, could be releasing these X-rays as they decay, he says.

Evidence one way or the other may be just around the corner. "Within a few years astronomers will be able to resolve compact objects at the centre of galaxies with radio interferometers," says Svidzinsky. Black holes will have a constant size, whereas an axion bubble's radius will oscillate, he says. Zioutas is looking forward to the answer.

"There is so much at stake here – rewriting both Einstein and dark matter," he says.

New Scientist - http://www.newscientist.com

Artist's impression of the binary system RS Ophiuchi. Hydrogen-rich gas is transferred from a red giant onto the surface of a white dwarf and has just exploded there. (David A. Hardy & PPARC)

However, we needed to use the world's most powerful radio telescopes because, from a distance of 5,000 light years, its apparent size on the sky was only 5 millionths of a degree - the size of a football seen from 2,700 km away."

The blast wave results from a huge nuclear explosion which takes place on the surface of one of a pair of stars, about 5,000 light years from Earth, which are closely circling one another. Gas captured from one star, a red giant, builds up on the surface of its white dwarf companion (a super-dense dead star about the size of the Earth which was once the core of a star like the Sun whose outer layers have been lost into space).

Eventually enough gas collects on the white dwarf for thermonuclear reactions to begin, similar to those which power the Sun but which runaway into a massive explosion. In less than a day, its energy output increases to over 100,000 times that of the Sun, and the gas (about the mass of the Earth) is thrown into space at speeds of several thousand km per second. This ejected matter then slams into the extended atmosphere of the bloated red giant and sets up blast waves that accelerate electrons to almost the speed of light. The electrons release radio waves as they move through a magnetic field that are then picked up by the telescope arrays.

First radio image of the blast wave taken with the VLBA telescope in the USA 14 days after the explosion. The colours relate to radio brightness with blue being faintest and red brightest. The binary star system itself would be at the centre but is invisible in this image. (NRAO /AUI /NSF)

Over the following months, the team continued to track the outburst using the European VLBI Network (EVN) which includes telescopes in South Africa and China, the MERLIN array of radio telescopes in the UK, and the Very Long Baseline Array (VLBA) and Very Large Array (VLA) in the USA, a truly global effort.

Dr Richard Porcas of the Max Planck Institute for Radio Astronomy in Bonn, who was also involved in the 1985 observing campaign of the last outbreak of RS Oph, coordinated the European VLBI Network observations. "A week after our first observations, we combined telescopes across Europe with two in China and another in South Africa and were surprised to find that the blast wave had become distorted.

Over the next few months our observations have shown it turning from a ring into a cigar-like shape. It's going to need a lot more work to understand exactly what causes this but either the explosion shoots jets of matter in opposite directions or somehow the atmosphere of the red giant is shaping the ejected material."

Once the outburst is over, gas will again build up on the white dwarf until at some point, maybe another 20 years in the future, RS Oph should explode again. An important question which the astronomers hope to answer is whether in each explosion the white dwarf throws off all the matter it has collected from the red giant or whether it is hoarding some material and therefore gradually increasing in mass.

Dr Tim O'Brien, who also studied RS Oph's previous outburst in 1985 for his doctoral thesis, concludes "If the white dwarf is increasing in mass then it will eventually be ripped apart in a titanic supernova explosion and the cycle of outbursts will come to an end."

Max Planck Institute for Radio Astronomy - http://www.mpg.de/english/institutesProjectsFacilities/instituteChoice/radioastronomie

Each paint sample was applied in a single layer to a wood block, left to dry and then removed and analyzed in UC laboratories for lead content.

About 50 percent of the paint sold in China, India and Malaysia—none of which appear to have regulations on lead—had lead levels 30 times higher than U.S. regulations. In contrast in Singapore, which has well-enforced regulations, only 10 percent of paint samples were above U.S. regulations, the highest being six times the U.S. limit.

Clark says he is concerned about children who are currently exposed to lead in their houses and neighborhoods—and for those who will live in such places in the future.

“Lead-based paints have already poisoned millions of children in the United States and will likely cause similar damage in the future as paint use increases in Asian countries and elsewhere,” he says. “Our findings provide stark evidence of the urgent need for an effective worldwide ban on the use of lead-based paint.”

Children are particularly susceptible to lead poisoning for a number of reasons, including their natural hand-to-mouth behaviors. Workers responsible for removing lead-based paint are also at high risk for lead poisoning.

In 1978, the United States restricted lead content in paint after determining that people—especially young children—were being poisoned by environmental exposures to the element. Many Third World countries, says Clark, did not follow suit, and continue to manufacture and sell lead-based paints that would be prohibited in the United States and in some other countries.

“We’ve known for years that there are good substitutes for lead in paint,” he continues, “so it’s absolutely incomprehensible that paint manufacturers—particularly large companies with plentiful resources—would knowingly distribute a product that can be dangerous to people.”

“Some lead-contaminated items intended for use by children, painted playground equipment, for example, are manufactured in countries with limited to zero government regulation on lead in consumer products,” says Clark.

Although American brand paints were not available for purchase in this study, several U.S. multinational paint companies are among the top in Asia and some Asian paint companies have arrangements with U.S. companies.

“American companies need to take a stand and encourage their international collaborators to demand lower lead contents in consumer products—including paint,” he adds. “It’s not only the ethical thing to do, it’s the fiscally responsible choice to prevent billions of dollars in future health costs and property clean-up costs.”

This research was funded by the UC’s environmental health department and division of occupational health and hygiene, with partial support from NITON Corporation for travel in China.

Collaborators in this study include Rebecca Clark and Sandy Roda of UC, Krishna Rampal, MD, of the University Kebangsaan Malaysia, Venkatesh Thuppil, PhD, of the National Referral Center for Lead Poisoning Prevention in India, and Chin Chen of the Occupational Safety and Health Center at Singapore Polytechnic.

The project will also look at how telepathic abilities may vary depending on the relationships which exist between participants.

The test is carried out using two volunteers who could be friends, work colleagues or family. They are placed in separate rooms on different floors of the same building to eliminate any possibility of communication. Participants enter the virtual environment by donning a head-mounted 3D display and an electronic glove which they use to navigate their way through the computer generated world.

Once inside participants view a random selection of computer-generated objects. These include a telephone, a football and an umbrella. The person in the first room sees one object at a time, which they are asked to concentrate on and interact with.

The person in the other room is simultaneously presented with the same object plus three decoy objects. They are then asked to select the object they believe the other participant is trying to transmit to them.

The system was designed by Dr Craig Murray of the School of Psychological Sciences, and implemented by Toby Howard and Dr Fabrice Caillette, from the School of Computer Science.

Dr Toby Howard said: "This system has been designed to overcome the many pitfalls evident in previous studies which could easily be manipulated by participants to produce an effect which looks like telepathy but is not.

"By creating a virtual environment we are creating a completely objective environment which makes it impossible for participants to leave signals or even unconscious clues as to which object they have chosen."

The system has been designed to make the task as realistic as possible. In addition to selecting objects and hearing the sounds they make, participants are able to hold and move them within the virtual environment.

Project researcher David Wilde, of the School of Psychological Sciences, said: "By using this technology we aim to provide the most objective study of telepathy to date. Our aim is not to prove or disprove its existence but to create an experimental method which stands up to scientific scrutiny."

The results of the experiment are expected to be published early in 2007.

University of Manchester - http://www.manchester.ac.uk

The dispersal of volcanic aerosols has a drastic effect on the Earth's atmosphere. Following an eruption, large amounts of sulphur dioxide (SO2), hydrochloric acid (HCL) and ash are spewed into the Earth's stratosphere. Hydrochloric acid, in most cases, condenses with water vapor and is rained out of the volcanic cloud formation. Sulphur dioxide from the cloud is transformed into sulphuric acid (H2SO4). The sulphuric acid quickly condenses, producing aerosol particles which linger in the atmosphere for long periods of time. The interaction of chemicals on the surface of aerosols and the tendency of aerosols to increase levels of chlorine which can react with nitrogen in the stratosphere, is a prime contributor to stratospheric ozone destruction. (NASA)

Aerosol particles in the mesosphere and stratosphere (NorFA)

This combination prevents atmospheric instability – the condition needed to form clouds and rain. A stable atmosphere means fewer clouds; fewer clouds mean less reflection of sunlight; less reflection of sunlight and absorption of radiation lead to warming.

Policy makers have argued that, in the bottom line, the warming effect of the greenhouse gases and the (mainly cooling) aerosol effect may balance each other out so that the net global climate change will be small.

Koren argues that it is the local climate change that is problematic: Clouds may persist without releasing their rain over regions where they would normally precipitate, such as rainforests, and move to precipitate over regions where rain is not needed, such as oceans. Or the effect could lead to the warming up of cold and the cooling down of hot regions. These additional effects to the already problematic warming by greenhouse gases could have disastrous repercussions in the long run.

Also controversial is the question of how such tiny localized particles affect weather systems thousands of kilometers away from their sources. There is no doubt that aerosols do play a role, but the skeptics believe it is negligible compared to meteorological key players such as temperature, pressure, the amount of water vapor in the air, and wind strength.

What Koren needed was a way to separate meteorological from aerosol influences – something which was lacking in his previous studies. Together with Kauffman, he used a network of ground sensors (AERONET) to measure the effect of aerosol concentration on cloud cover. Radiation absorption is less affected by meteorology, so if the skeptics are right and meteorology is the main influence, then the correlation between aerosol absorption and cloud cover should have been seen in only a few circumstances. But this was not the case.

They observed the duality effect on clouds: As total aerosols increase, cloud cover increases; and as radiation absorption by aerosols increases, cloud cover decreases – for all locations, for all seasons. Backed up with a mathematical analysis, it becomes harder to deny that it is, in fact, aerosols that have the major influence.

"We hope that this study has finally provided closure," says Koren. "Hopefully policy makers will start to tackle the issue of climate change from a different perspective, taking into account not only the global impact of aerosols and greenhouse gases, but local effects too."

American Committee for the Weizmann Institute of Science - http://www.weizmann-usa.org

The work, Mapping the Future, is the result of collaboration between CCSR, Hunter College and Population Action International (PAI) and was released this spring in conjunction with an update of PAI’s Web feature, People in the Balance, investigating the relationship between human population and critical natural resources.

A section of the new population map created by the Center for Climate Systems Research shows increasing populations in coastal areas, which will expose 2.75 billion people worldwide to the effects of sea level rise and other coastal threats posed by global warming. (EICU)

The map indicates that the greatest increases in population density through 2025 are likely to occur in areas of developing countries that are already quite densely populated.

In addition, the number of people living within 60 miles of a coastline is expected to increase by 35 percent over 1995 population levels, exposing 2.75 billion people worldwide to the effects of sea level rise and other coastal threats posed by global warming.

The map also projects that much of southern and Eastern Europe and Japan will experience significant and wide-spread population decline.

Surprisingly, the map further suggests small areas of projected population decline for many regions in which they might be least expected: sub-Saharan Africa, Central and South America, the Philippines, Nepal, Turkey, Cambodia, Burma and Indonesia — areas that have to date been experiencing rapid-to-modest national population growth.

"By bridging these two areas of demography — mapping and long-range, aggregate projections — we're getting a better idea of where people are likely to live in the future and why," said Stuart Gaffin, associate research scientist at CCSR and lead scientist on the project. "Hopefully, work like ours will play a central role in improving environmental policies around the world and in reducing natural hazard risks faced by the most vulnerable parts of society."

Where most projections show future global population for each of more than 200 countries, Mapping the Future displays the projected population for each of nine million cells distributed across the globe. Known as "downscaling," this new arena of spatial analysis and demography is expected to be of particular interest to conservationists, climate specialists and others who need to know where people will live, and in what numbers, in coming decades and in extremely fine detail. The data may also provide a "best guess" of regional populations that might be most susceptible to natural disasters in the future.

"We already have a pretty good idea of how the population of individual countries is likely to change in coming years," said Gaffin. "This map pushes the frontier on projecting high-resolution, sub-national populations so we can begin to examine how internal population dynamics might play out against other environmental, ecological and socio-economic concerns."

To produce the map, Gaffin and his colleagues extrapolated population changes that occurred between 1990 and 1995 out to 2025 in each grid cell. They selected from two methods to arrive at the best and most likely fit consistent with the UN's "medium variant" projection for each country’s population: one based on a particular cell's changing fractional share of the overall national population and another based on the cell's share of national growth during the 1990s.

Download page for hi-res full-size map - http://www.ccsr.columbia.edu/population/map

The Earth Institute at Columbia University - http://www.ldeo.columbia.edu

Unmanned solar-powered planes will act as as high-altitude platforms (HAPs) to relay wireless and optical communications. (NASA)

HAP airship design.

The final experimental flight will use a US-built Unmanned Aerial Vehicle (UAV) and will take place in Arizona days before the York HAP Week conference at the city's historic King's Manor.

Following the CAPANINA event, a HAP Application Symposium led by Dr Jorge Pereira, of the Information Society and Media Directorate-General of the European Commission, will provide a forum for leading experts to illustrate the potential of HAPs to opinion formers and telecommunications providers.

Completing the week will be the first HAPCOS Workshop, featuring the work of leading researchers from around Europe. It will focus on wireless and optical communications from HAPs, as well as the critically important field of HAP vehicle development.

The Chair of HAPCOS, Tim Tozer, of the University of York's Department of Electronics, said: "There are a number of projects worldwide that are proving the technology and we want to convince the telecommunications and the wider community of its potential. We are particularly keen to attract aerial vehicle providers."

The CAPANINA and HAPCOS activities have helped to forge collaborative links with more than 25 countries, including many from Europe, as well as Japan, South Korea, China, Malaysia and USA. They are seeking to develop existing partnerships and forge new ones, with researchers, entrepreneurs, industry, governments as well as end users.

University of York - http://www.york.ac.uk