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2) Black holes bend light the 'wrong' way

Refraction effect may be distorting astronomers' results

Astronomers could be misinterpreting their observations of distant stars, suggest mathematicians.

Starlight may be bent in odd directions when it passes close to a rotating black hole, the researchers say, unexpectedly shifting its source's apparent position in the sky. The cause is a recently discovered phenomenon called negative refraction, which physicists are still struggling to understand.

Astronomers already adjust their observations to account for the fact that light is bent by massive objects such as black holes, an effect called gravitational lensing. But Akhlesh Lakhtakia, a mathematician at Pennsylvania State University in University Park, has studied what happens when a black hole rotates. In this case, light is bent in the direction opposite to that predicted by conventional theory.

"Astronomical measurements, particularly those relating to black holes and other massive stellar bodies, need careful reinterpretation," says Tom Mackay of the University of Edinburgh, UK, who worked with Lakhtakia on the analysis, published online in Physics Letters A (Ref. 1).

Negative refraction is new to astronomy, but has been causing a stir in materials science in recent years. When light crosses a boundary, it is bent in a characteristic way; this is why an oar dipped in water looks as though the submerged part is angled towards the surface.

But in 2001, US researchers showed that certain artificial materials bend light in the opposite direction (Ref. 2). If water had this property, the submerged oar would appear to angle away from the surface

The revelation prompted a flurry of research, most of which has focused on understanding and developing negative refracting materials. "But this is exactly the same phenomena," Mackay points out.

Last year, Mackay and Lakhtakia demonstrated that negative refraction could occur in a vacuum, provided that the gravitational field in the region had the right properties. Now, they have identified something that meets these requirements: a rotating black hole. Very large rotating stars would have the same effect, adds Mackay.

This might force astronomers to rethink some of their observations. "The deflection of light could be significant," says Mackay. In theory, starlight could even turn through a 90° angle, apparently putting the star in a completely different part of the sky. "And the further away the object is, the more likely it is that these effects are interfering with observations," adds Mackay.

However, some researchers question how much influence the effect will have in practice. Matthias Bartelmann, a theoretical astrophysicist at the University of Heidelberg in Germany, describes Mackay and Lakhtakia's paper as very interesting. "But I'm in doubt as to the astronomical relevance," he says. Bartelmann points out that the effect will be limited to small regions of space, as it can only occur in regions where the gravitational field is extremely strong.

The effect could find other uses, however. Theoretical astronomers are currently debating whether the cosmological constant, a key number in the equations that describe the evolution and growth of the universe, is positive or negative. Mackay says that negative refraction can only take place if the constant is positive, so experimental verification of such refraction could help to settle the debate.

1. Lakhtakia A., Mackay T. G. & Setiawan S. Phys. Lett. A, 336. 89 - 96 (2005).
2. Shelby R. A., Smith D. R. & Schultz S. Science, 292. 77 - 79 (2001).

Residential energy use in the United States will increase 25 percent by the year 2025, according to U.S. Department of Energy (DOE) forecasts. A small but increasing share of that extra power will trickle in from renewable sources like wind, sunlight, water, and heat in the ground.

Last year alternative energy sources provided 6 percent of the nation's energy supply, according to the DOE.

"The future belongs to renewable energy," said Brad Colllins, the executive director of the American Solar Energy Society, a Boulder, Colorado-based nonprofit. Scientists and industry experts may disagree over how long the world's supply of oil and natural gas will last, but it will end, Collins said.

While renewable energy is generally more expensive than conventionally produced supplies, alternative power helps to reduce pollution and to conserve fossil fuels.

"People sometimes get caught up in cost-effectiveness," said Paul Torcellini, a senior engineer at the DOE's National Renewable Energy Laboratory (NREL) in Golden, Colorado. "But it can be a question of values and what we spend our money on."

Below, a look at some recent developments in renewable-energy technology:

Solar Power

Photovoltaic, or solar-electric, systems capture light energy from the sun's rays and convert it into electricity. Today these solar units power everything from small homes to large office buildings.

Technological improvements have made solar-electric modules more cost-effective. In the 1980s the average price of energy captured with photovoltaics was 95 U.S. cents per kilowatt-hour. Today that price has dropped to around 20 cents per kilowatt-hour, according to Collins, of the American Solar Energy Society.

The cheaper rate is still more expensive than the average national price of electricity, which in 2003 was a little over 8 cents per kilowatt-hour, according to the U.S. Department of Energy's Annual Energy Review.

Other recent advances include "thin film" photovoltaic technology, a high-tech coating that converts any surface covered with the film into a solar-electric power source.

Boats and RVs that use the film are now on the market.

Engineers have also developed a roofing material coated with the electricity-producing film. "The guy who puts on the roof [on a house now] puts on the [solar] panels at the same time," Torcellini said. The roofing material withstands inclement weather and, on bright days, taps sunshine for electricity.

NREL researchers, meanwhile, are working to devise more efficient and cheaper solar-electric systems. Most traditional photovoltaic solar units on the market today convert between 11 and 13 percent of the sun's light into energy. Engineers think they can improve on that.

Jeff Mazer, a Washington, D.C.-area photovoltaic engineer, notes that most thin-film photovoltaic systems today have a 7 to 11 percent efficiency rating. But he estimates that thin films could surpass that rating within three years. He also notes that some new traditional solar modules achieve 15 percent efficiency and believes that figure can climb to 17 percent in the near future.

In the last two decades solar-thermal panels (units used to warm household hot water, pools, and spas) have become highly efficient. Energy costs have decreased from 60 cents to 8 cents per kilowatt-hour since the 1980s, Collins said.

Solar-powered water heaters are typically more expensive than conventional ones, but, as with other products that harness alternative energy, consumers benefit by knowing their energy costs up-front, Torcellini said. "Otherwise, you're hedging your bets about the future cost of [traditional] energy [sources] by using standard appliances," he said.

Wind Power

Compared to other renewable energy sources, wind power competes with conventional energy at a price less than 4 cents per kilowatt-hour, Collins said.

Wind energy projects around the world now generate enough energy to power nine million typical U.S. homes, according to the American Wind Energy Association, a Washington, D.C.-based trade group.

One of the newest trends in wind power is the construction of offshore wind farms, clusters of electricity-generating turbines erected in open-water areas with strong winds.

Europe now has 17 wind farms spinning offshore. The Arklow Bank Offshore Wind Park, 8 miles (13 kilometers) off the eastern coast of Ireland, is one such project. Its seven turbines generate enough electricity to power 16,000 homes.

While few homes generate their own wind power in the U.S., many power companies allow consumers to opt for power generated at a wind plant or other renewable source.

On Tuesday, Colorado voters will consider a ballot initiative that would require power companies to provide 10 percent of their electricity from wind and other renewable sources by 2015.

"If that passes, power companies will offer more rebates to homeowners" to encourage renewable energy production, said Sheila Hayter, an NREL senior engineer.

Ground Heat

Tapping into the ground offers another option to regulate household heating and cooling.

In most areas of the United States, the ground below the frost line maintains an average temperature between 50 and 54 degrees Fahrenheit (10 to 12 degrees Celsius).

Ground-source heat pumps, also called geo-exchange systems, use this relatively constant temperature to keep homes at comfortable temperatures.

The devices employ a series of underground, liquid-filled tubes or wells. Liquid flows through the pipes into the home, where a heat exchanger either adds or subtracts heat from indoor air, depending on the season. In winter, that means added warmth captured from the ground.

"If you can [do that], your furnace doesn't have to work so hard," Hayter said.

A U.S. Environmental Protection Agency study found that geo-exchange systems can save up to 70 percent of home-heating costs.

On February 17, important clean energy legislation was introduced in Congress. The Renewable Electricity Standard (RES) requires utilities to gradually increase their use of clean energy–-such as wind and solar power–-to 20 percent of total power generation. A strong national RES would not only decrease pollution and global warming emissions, but would also increase our energy independence and create hundreds of thousands of new jobs. Please urge your members of Congress to support a clean energy future for America and insist that any national energy legislation must contain a strong RES.

The U.S. Senate has twice passed a moderate 10 percent Renewable Electricity Standard (RES) as part of broader energy legislation, but House leadership opposed the provision. In both the 107th and 108th Congress, the RES died along with the rest of the energy bill during the effort to resolve differences between the House and Senate bills. To secure final passage of a strong RES, we need to strengthen existing Senate support and build greater support among House Republicans.

Move toward a cleaner energy future by co-sponsoring a strong RES bill (HR 983/ S. 427) and insisting that any national energy legislation must include a strong RES.

Scientists have invented a plastic solar cell that can turn the sun's power into electrical energy, even on a cloudy day.

The plastic material uses nanotechnology and contains the first solar cells able to harness the sun's invisible, infrared rays. The breakthrough has led theorists to predict that plastic solar cells could one day become five times more efficient than current solar cell technology.

Like paint, the composite can be sprayed onto other materials and used as portable electricity. A sweater coated in the material could power a cell phone or other wireless devices. A hydrogen-powered car painted with the film could potentially convert enough energy into electricity to continually recharge the car's battery.

The researchers envision that one day "solar farms" consisting of the plastic material could be rolled across deserts to generate enough clean energy to supply the entire planet's power needs.

"The sun that reaches the Earth's surface delivers 10,000 times more energy than we consume," said Ted Sargent, an electrical and computer engineering professor at the University of Toronto. Sargent is one of the inventors of the new plastic material.

"If we could cover 0.1 percent of the Earth's surface with [very efficient] large-area solar cells," he said, "we could in principle replace all of our energy habits with a source of power which is clean and renewable."

Infrared Power

Plastic solar cells are not new. But existing materials are only able to harness the sun's visible light. While half of the sun's power lies in the visible spectrum, the other half lies in the infrared spectrum.

The new material is the first plastic composite that is able to harness the infrared portion.

"Everything that's warm gives off some heat. Even people and animals give off heat," Sargent said. "So there actually is some power remaining in the infrared [spectrum], even when it appears to us to be dark outside."

The researchers combined specially designed nano particles called quantum dots with a polymer to make the plastic that can detect energy in the infrared.

With further advances, the new plastic "could allow up to 30 percent of the sun's radiant energy to be harnessed, compared to 6 percent in today's best plastic solar cells," said Peter Peumans, a Stanford University electrical engineering professor, who studied the work.

Electrical Sweaters

The new material could make technology truly wireless.

"We have this expectation that we don't have to plug into a phone jack anymore to talk on the phone, but we're resigned to the fact that we have to plug into an electrical outlet to recharge the batteries," Sargent said. "That's only communications wireless, not power wireless."

He said the plastic coating could be woven into a shirt or sweater and used to charge an item like a cell phone.

"A sweater is already absorbing all sorts of light both in the infrared and the visible," said Sargent. "Instead of just turning that into heat, as it currently does, imagine if it were to turn that into electricity."

Other possibilities include energy-saving plastic sheeting that could be unfurled onto a rooftop to supply heating needs, or solar cell window coating that could let in enough infrared light to power home appliances.

Cost-Effectiveness

Ultimately, a large amount of the sun's energy could be harnessed through "solar farms" and used to power all our energy needs, the researchers predict.

"This could potentially displace other sources of electrical production that produce greenhouse gases, such as coal," Sargent said.

In Japan, the world's largest solar-power market, the government expects that 50 percent of residential power supply will come from solar power by 2030, up from a fraction of a percent today.

The biggest hurdle facing solar power is cost-effectiveness.

At a current cost of 25 to 50 cents per kilowatt-hour, solar power is significantly more expensive than conventional electrical power for residences. Average U.S. residential power prices are less than ten cents per kilowatt-hour, according to experts.

But that could change with the new material.

"Flexible, roller-processed solar cells have the potential to turn the sun's power into a clean, green, convenient source of energy," said John Wolfe, a nanotechnology venture capital investor at Lux Capital in New York City.