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Record-Setting Star
| More than two decades of research has resulted in a major find for astronomy — a star with a record number of planets, and according to experts, it’s just the beginning.
“The chance of our planet being the only one seems vanishingly small,” John Brewer, an astronomy graduate student at San Francisco State University in California, told Ivanhoe. In the constellation of cancer, astronomer Debra Fisher and her students discovered that a star called 55 Cancri has something no other star outside of our solar system has — five planets orbiting it. That’s a record! “Just finding a system that is so full of planets tells us that planet formation is easy,” Debra Fischer, astronomer at San Francisco State University, told Ivanhoe. For students, sharing in a discovery puts stars in their eyes. “Although you can learn from books, the cutting edge research that’s being done now, the new research isn’t in the books,” Brewer explained. “It’s with the research scientists that are performing the studies.” According to Fischer, this fifth planet is special because it orbits at what’s called the “goldilocks” distance, where the temperature isn’t too hot or too cold to support liquid water, a key characteristic for life. “The theorists are predicting that there are still other planets around 55 Cancri,” Fischer said, “so we’re going to keep looking for them there.” This is a quest 41 light years from Earth. One planet can take 14 years to orbit around a star, so discovering planet number six may take a while, but these students will soon be the researches that keep looking.
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Frequency comb reaches extreme ultraviolet
Physicists in the US have created an optical frequency comb that operates in the extreme ultraviolet (XUV). Touted as the first practical comb to work in this region of the spectrum, the device could be used to look for tiny variations in the fine-structure constant and other physical constants that could point to new physics. An XUV comb could also be used to create better atomic clocks and new techniques for atomic spectroscopy.
Frequency combs are created with an ultrafast mode-locked laser, in which pulses of light bounce back and forth in an optical cavity. The frequency spectrum of the resulting train of pulses from such a laser is a series of very sharp peaks that are evenly spaced in frequency, like the teeth on a comb.
When one comb “tooth” is set to a standard frequency – such as that generated by an atomic clock – the absolute frequency of another light source can be measured to great accuracy by comparing it with the other teeth on the comb. The device therefore offers researchers a way of making very accurate spectroscopic measurements of atoms and molecules, and also a way of comparing atomic clocks.
Current combs operate at optical frequencies, and physicists have struggled to extend them into the ultraviolet and beyond. One promising path is a process called high-harmonic generation (HHG), whereby an intense laser ionizes atoms in a gas and then accelerates the electrons causing them to radiate high-frequency photons. HHG has already been used to create pulses of XUV light, but not trains of pulses that are of high enough quality to create a practical XUV comb.
A fine comb
One difficulty in making a practical XUV comb is ensuring that successive pulses have a high degree of phase coherence over time periods as long as seconds. Another challenge is making the pulses intense enough so that the comb can be used to perform atomic spectroscopy experiments. Now, however, Jun Ye and colleagues at the Joint Institute for Laboratory Astrophysics (JILA) in Boulder, Colorado, are the first to demonstrate a technique that addresses both of these problems.
The technique uses a high-power laser to create an intense infrared comb within an optical cavity. The cavity is then filled with xenon gas, which provides the medium for HHG, whereby the intense infrared pulses create pulses of XUV light. These XUV pulses bounce back and forth in the cavity to create a second comb. According to Ye, much of the glory for the demonstration should go to Ingmar Hartl and colleagues at the Michigan-based firm IMRA America, who designed and supplied the high-power laser.
Krypton factor
The comb was also operated using krypton as the HHG gas. In both cases, the team was able to create combs of light in the 40–120 nm wavelength range, which corresponds to XUV light. To demonstrate the comb, Ye and colleagues used it to study specific atomic transitions in argon and neon at wavelengths of 82 nm and 63 nm, respectively. In both cases they showed that light from a single tooth of the comb was intense enough to resolve the transitions. Patrick Gill of the UK’s National Physical Laboratory described the work as “a good example of using the comb mode of HHG to do single-photon spectroscopy in the XUV”.
Ye told physicsworld.com that the comb opens the door to a wide range of new measurements, including tests of single- and two-body quantum theory in atom-like systems. The combs could also be used in next-generation “nuclear clocks”, which are based on nuclear transitions and “tick” at higher frequencies than atomic clocks. Other important applications could be laboratory and astrophysical measurements of variations of fundamental constants such as the fine-structure constant – which could point to physics beyond the Standard Model.
Ted Hänsch at LMU Munich described the work as “an important milestone on the path towards routine use of XUV frequency combs for spectroscopy”. Hänsch – who shared the 2005 Nobel Prize for Physics for the invention of the frequency comb – told physicsworld.com “I am optimistic that frequency-comb techniques can be pushed to shorter wavelengths, but the required mutual phase coherence of successive pulses will make it rather challenging to reach the X-ray regime.”
Magnetic fields put the brakes on millisecond pulsars
A researcher in Germany has revealed how “millisecond pulsars” – neutron stars with rotational periods ranging from 1–10 ms – slow over time. By exploring how a pulsar behaves when it stops accreting matter from a donor star, Thomas Tauris from the University of Bonn has shown quantitatively that it is the expansion of the pulsar’s magnetic field that helps to slow the star’s rotation. The finding may help astronomers to determine the age of radio millisecond pulsars, which is usually calculated based on the rate at which the pulsars’ rotation slows.
Pulsing stars
Neutron stars are highly compact remnants from exploding stars known as supernovae. As they retain most of the original star’s angular momentum but have much smaller radii, neutron stars rotate at very high speeds when they are formed. They also appear to pulse as they rotate, just like a lighthouse beam. The pulse arises from interactions between an electrical field created by the rotational energy of the neutron star and the star’s very strong magnetic field, which create an electromagnetic beam emanating from the poles of the magnetic field.
Pulsars can glow for 50 to 100 million years after the original explosion, emitting radio waves until they run out of energy and go dark. But for pulsars orbiting with companion stars, this does not spell the end. As the companion reaches the end of its hydrogen-burning phase, it begins to expand, allowing the neutron star to lift material from its surface. The filched plasma effectively breathes new life into the neutron star. The charged particles of the plasma get caught in its magnetic field and are funnelled along the magnetic field lines toward the poles. Heating through friction and impact with the pulsar’s surface causes the plasma to emit X-rays, which emanate most strongly from the magnetic poles.
Hidden transitions
As the mass moves in towards the star’s surface, the plasma also causes the star to spin faster, like a figure skater pulling in their arms. But when the companion star has given off all its envelope material, the pulsar begins to slow and emits radio waves instead of X-rays. Indeed, the 13 known accreting X-ray millisecond pulsars have an average rotation period of 3.3 ms, whereas the 200 known millisecond pulsars that emit radio waves – with spin periods of less than 20 ms – have a slower average period of 5.5 ms.
But little is known about what happens to these pulsars during this transition from emitting X-ray to emitting radio waves. Because the radio-emitting millisecond pulsars were once X-ray emitters, Alessandro Patruno of the University of Amsterdam in the Netherlands, who was not involved in the current work, says it is like accelerating a spinning top only to let it go and find it abruptly spinning more slowly. “For this to happen something must have slowed the rotation after you finished accelerating the spinning top,” he says. That braking seems to occur as the flow of matter from the donor star gradually shuts off.
Hit the breaks
What Tauris has done is to show that as the flow of plasma from the companion star tails off, the star’s magnetic field expands outwards to about 100 km, or roughly 10 times the neutron star’s radius. “The magnetosphere acts like a long lever arm, amplifying the effects of the last plasma,” explains Tauris. This means that interactions between the magnetic field and the plasma become magnified. For example, the field might blast away some of the matter away, instead of accreting it, and these interactions cut the star’s rotational energy by as much as half.
Fred Lamb, an astrophysicist at the University of Illinois, Urbana-Champagne, calls Tauris’s finding “a significant advance in our understanding of how accreting millisecond X-ray pulsars become rotation-powered millisecond radio pulsars”. He adds that while importance of this phase has been known for many years, “until this work by Tauris, no calculations modelling this phase had been performed”.
Synchronizing clocks
This slowing mechanism also sheds new light on the question of why radio millisecond pulsars seem so much older than their companions. After giving up most of its gas, the companion star can no longer burn hydrogen, but it is still hot – a white dwarf. The temperature of the white dwarf gives one measure of a binary system’s age. As a pulsar’s age is calculated based on how much its rotational period slows, this unexpected slowing leads to the age discrepancy.
In millisecond pulsars, Tauris says this method gives “ridiculous” ages such as 15 billion years – longer than the age of the universe. The dramatic deceleration as the neutron star is cut off from its donor can explain why these stars often appear much older than their companions. “There’s only one reliable clock and that’s the cooling of the white dwarf,” says Tauris.
Tauris acknowledges that the number of X-ray millisecond pulsars he could consider is relatively small as they were only discovered a decade ago. More observations of these stars, to be made with current and future X-ray satellites such as NASA’s Rossi X-ray Timing Observer, will put Tauris’s picture to the test.
Nanoshells could boost photovoltaics
Researchers in the US have reported on a new way to increase the amount of light absorbed by thin-film solar-cell materials. The new technique relies on “whispering gallery” modes in which light becomes trapped inside tiny shells made of silicon. The result could lead to more efficient photovoltaics, claims the team.
Nanocrystalline silicon could be ideal for making photovoltaic devices because it is an excellent conductor of electricity and can withstand harsh sunlight without suffering any damage. However, there is a problem: silicon does not absorb light very efficiently. Layers of the material have to be built up to increase the amount of light absorbed – a process that is both time-consuming and expensive.
Now, Yi Cui and colleagues at Stanford University have shown that nanoshells made of silicon could offer a quicker and cheaper route to solar-cell fabrication. The cavity inside such a structure confines light in a “whispering gallery” mode, whereby the light orbits around the edge of the cavity at precise resonant frequencies as a result of total internal reflection. “Light effectively gets trapped in these hollow shells,” explains Cui. “It circulates round and round rather than just passing through, and this is very desirable for solar applications because the longer the light is kept in the material, the better its absorption will be.”
Silica balls
The researchers created their nanoshells by first fabricating balls of silica just 50 nm in size and coating these with a layer of silicon. Next, they etched away the glass centre of the shells using hydrofluoric acid. The acid does not attack the surrounding silicon layer and so the technique produces a light-sensitive silicon shell.
The nanoshells can be made in a matter of minutes. In contrast, a micrometre-thick flat film of solid nanocrystalline silicon with equivalent light-absorbing properties would take a few hours to deposit. The nanoshells also absorb light over a broader spectrum than the flat layer of silicon.
And that is not all: a significantly smaller amount of material is required to make a nanoshell compared with a flat silicon slab – roughly 5%, according to Cui and co-workers. This is something that could obviously bring down processing costs. “Looking down the road, the fact that much less material is required to make these nanoshells might come in useful when manufacturing many other types of thin-film cells, such as those that use rarer, more expensive materials like tellurium and indium,” he told physicsworld.com.
New applications
The nanoshells are also fairly indifferent to the angle of incoming sunlight hitting them and the layers are able to bend and twist without becoming damaged. “All these factors might open up an array of new applications in situations where optimal exposure to the angle of the Sun is not always possible,” adds Cui. “Imagine solar sails on the high seas or photovoltaic clothing for mountain climbing, for example.”
Having performed detailed theoretical calculations on the nanoshells, the researchers are now busy making real cells from silica. “We are also exploring the structures to see if they can be used in other types of applications, such as solar fuels and photodetectors as well,” reveals Cui.
Endangered primate ‘talks’ using ultrasound
The Philippine tarsier (Tarsius syrichta) is a petite, nocturnal primate that lives on a diet of insects. It is the first documented example of primate that communicates with purely ultrasonic frequencies.
Credit: rajawaseem6
SYDNEY: A shy, wide-eyed and nocturnal species called the Phillipine tarsier is the first primate to be identified as having the ability to communicate in purely ultrasonic frequencies.
A new study published in Biology Letters today has revealed that the endangered Philippine tarsier (Tarsius syrichta) communicates using sound with a frequency greater than 20 kilohertz. The finding contradicts conventional thinking that all primate vocalisations are audible to humans.
“We found that the Philippine tarsier can hear higher pitched sounds than any other primate, and that it also has the highest pitched primate vocalisation ever documented! What we thought was a quiet species may actually be a species that has a variety of vocalisations that we had no knowledge of, simply because we could not hear them,” said first author and biological anthropologist Marissa Ramsier from Humboldt State University in Arcata, California.
“Although it is possible that the Philippine tarsier is unique in its ability, it is exciting to think about all of the animals, primates and non-primates alike, that may be communicating in ways that we have not yet realised. Many of my colleagues have noted silent mouth-opening behaviours in a wide range of species. There could be entire sets of signals out there waiting to be heard!” she added.
Tarsiers are good listeners
A select group of mammals including bats, rodents, domestic cats and aquatic cetaceans (whales, dolphins and porpoises) are known to communicate with pure ultrasound, but until now researchers were unaware that primates had the same capability.
Over the past four years, Ramsier and colleagues have studied the hearing sensitivity of over 20 primate species. “We actually know very little about how and why primate species vary in their hearing abilities. [It turns out that] even closely related species can vary in their auditory sensitivity, likely owing to differences in diet, competition, predator pressure, and habitat,” she said. “We decided to look at the tarsier because it is a very unique primate.”
The tarsier’s nearest relatives belong to a group of primates called Anthropoidea including monkeys, apes and humans. However, as a petite, nocturnal species that eats mainly insects, the tarsier has more in common with species in Prosimii, a distantly related primate group that includes lemurs. And unlike most nocturnal animals, the tarsier also lacks a tapetum lucidum, which is a layer of tissue many vertebrate animals have in their eyes, which creates an effect known as ‘eye shine’. Rather than maximising light detection in this way, tarsiers have the largest eyes relative to body size of any mammal.
Minimally invasive testing
The researchers tested the hearing and vocalisations of six individuals found in the wild using technology developed by the U.S. Navy Marine Mammal Program. The technology measures the response of the brain stem to auditory stimuli. The stimuli comprised a series of tones ranging in pitch and loudness, played through a speaker.
The neurologic response of the tarsiers was then measured using electroencephalography – the same technique used in medicine where electrodes attached to the head record brain activity. The minimally invasive technique enabled measurements to be performed within about an hour and without animal training, after which each individual was released back into the wild, unharmed.
Ramsier and her co-researchers discovered the tarsiers could hear sounds up to 91 kHz, around five times the hearing limit of most humans. They also recorded vocalisations with a dominant frequency of 70 kHz.
First portable invisibility cloak created
The hexagonal invisibility cloak sample.
Credit: rajawaseem6
SYDNEY: A device that can make objects invisible under visible light has been created, and unlike past cloaking devices, it doesn’t need a reflective surface, so is completely portable.
A study published in Nature’s Scientific Reports journal describes the creation of a sample cloaking device that looks like a hexagon when viewed from above, and can make an isolated cylindrical object invisible in six directions. The sample is based on a theoretical design of a portable device that can render objects invisible in all directions, which brings the goal of a fully movable invisibility cloak one step closer to reality.
“Based on previous theory of transformation optics, we showed a scheme to design an isolated polygonal cloak for visible light using simple electromagnetic parameters,” said co-author of the study, Hongsheng Chen from the Electromagnetics Academy at Zhejiang University in Hongzhou, China. “In the visible light frequencies, it is the first design of a moveable directional cloaking device.”
Previous invisibility devices
Previous studies have designed and created devices that work as invisibility cloaks thanks to a mathematical approach called transformation optics, which describes what material properties are needed to guide light.
In order to render an object invisible, light is shone on the device and passed around the object inside to go back onto its original path. This makes the light look like it travelled in a straight line through the device as if nothing was in the middle. These devices have commonly made objects invisible under microwaves, but researchers have wanted to create a device that works under visible light so they can be used in real world applications.
‘Carpet cloaking’ has been a popular technique for invisibility devices because it allows the use of visible light. But it requires a reflective surface like a mirror. Such devices are able to conceal larger objects but are restricted in their portability.
Special crystals
Chen’s team created a simplified hexagonal cloak based on their theoretical model. It is a small box with six sides and six directions of invisibility, made from a particular type of natural material that does not behave the same way in all directions. The device concealed a macroscopic cylindrical item with a maximum diameter of 3mm.
The materials required for this sample device are called anisotropic birefringent materials, which are extremely hard to come by, but according to the researchers are the ideal for creating a device that could make objects invisible in all directions.
“[Birefringent] material properties are helpful to guide the rays with a specific polarisation in the right way – flowing around the cloaked object and appearing on the other side without any deviation. In such a way, an observer cannot tell that the light flowed around the hidden object or not,” said Chen. “Anisotropy provides an ability to bend the light in an unusual way at the interface of two medium and thus can be very helpful to achieve an omni-directional cloak with a large cloaking area.”
From theoretical to practical
Creating a real onmi-directional cloaking device will depend on obtaining these rare materials, so the launch of a device that can conceal large objects from all directions is not in the near future. However, as research into this field increases, Chen said that it will not be that long before a directional cloak is created that will be capable of concealing larger items such as a tennis ball or a human being from several directions.
Physicist David Powell from the Nonlinear Physics Centre at the Australia National University in Canberra, who was not involved in the study, said that this experiment is “quite visually impressive, in the sense that you can actually see the cloaking effect in action, and the cloaked object is quite large.” He said that the work is an advance over previous studies, but not a huge leap.
Powell pointed out that there are major obstacles to creating a “fully 3D cloak”, in that this device only works for light of a certain polarisation and the cloak itself reflects light, so it can be seen even if the object inside cannot.
Exotic new particles discovered
The Collider Detector at Fermilab which was used to accelerate the protons and antiprotons and measure the new subatomic particles formed.
Credit: rajawaseem6
SYDNEY: Two new subatomic particles have been found by recreating conditions at the beginning of the universe, according to a new international study.
The particles are exotic relatives of the proton and neutron.
“These particles, named Sigma-sub-b, are like rare jewels that we mined out of our data,” said Jacobo Konigsberg of the University of Florida, a spokesperson for the project.
The team of physicists at the Fermi National Accelerator Laboratory in Illinois, USA, fired protons and antiprotons (which have the same mass as protons but opposite charge) at each other at close to the speed of light.
This allowed them to reproduce the strange matter that was abundant in the ultra-high energy conditions moments after the Big Bang.
After creating billions of these subatomic car crashes, the researchers observed just 240 of the rare Sigma-sub-b particles.
In the collisions, the energy of the speeding protons was converted into mass (in accordance with Albert Einstein’s famous equation E = mc2), however the particles decayed in a fraction of a second.
“It’s amazing that scientists can build a particle accelerator that produces this many collisions, and equally amazing that the collaboration was able to develop a particle detector that can measure them all,” said co-spokesman Rob Roser, of Fermilab.
The particles are part of the baryon family of subatomic particles, which includes protons and neutrons. Baryons are made up of three quarks, one of the fundamental building blocks of matter.
The term ‘baryon’ comes from the Greek word ‘barys’, meaning ‘heavy’, because when the term was created, it was believed that members of the baryon group were heavier than other types of particles.
The two new particles are the heaviest baryons yet found – six times heavier than a proton – making them weightier than a complete helium atom, which has two protons.
“These newest members of [the baryon] family are unstable and ephemeral, but they help us to understand the forces that bind quarks together into matter,” said team leader Petar Maksimovic of Johns Hopkins University in Baltimore, Maryland.
Normal matter around us, including protons and neutrons, is made up of only two types of quarks, called ‘up’ and ‘down’ quarks. In total there are six types of quarks – up, down, strange, charm, bottom and top.
Of the new particles, 103 were positively charged and made of two up quarks and one bottom quark, while 134 were negatively charged particles made of two down quarks and a bottom quark.
“Little by little, we are compiling an ever-clearer picture of how quarks build matter and how subatomic forces hold quarks together and tear them apart,” said Maksimovic.
The discovery has confirmed theorists’ predictions of the existence of Sigma-sub-b particles and has helped to complete what the physicists call the periodic table of baryons.
“We are confident that our data hold the secret to even more discoveries that we will find with time,” said Roser.
e=mc2: 103 years on, Einstein proved right
Credit: rajawaseem6PARIS: Einstein’s celebrated formula e=mc2 has been corroborated (again), thanks to a heroic computational effort by French, German and Hungarian physicists.
A brainpower consortium led by Laurent Lellouch of France’s Centre for Theoretical Physics, using some of the world’s mightiest supercomputers, have set down the calculations for estimating the mass of protons and neutrons, the particles at the nucleus of atoms.
Energy and mass are equivalent
According to the conventional model of particle physics, protons and neutrons comprise smaller particles known as quarks, which in turn are bound by gluons.
The odd thing is this: the mass of gluons is zero and the mass of quarks is only five percent. Where, therefore, is the missing 95 per cent?
The answer, according to the study published in the U.S. journal Science today, comes from the energy from the movements and interactions of quarks and gluons.
In other words, energy and mass are equivalent, as Einstein proposed in his Special Theory of Relativity in 1905. The e=mc2 formula shows that mass can be converted into energy, and energy can be converted into mass.
Last year a different stream of evidence from particle accelerators also corroborated the theory (see, Einstein is still right on time). Yet another study of pulsars backed-up Einstein’s General Theory of Relativity in 2006 (see, The stars say Einstein was 99.95 per cent right).
Inspiration for atomic weapons
By showing how much energy would be released if a certain amount of mass were to be converted into energy, the equation has been used many times, most famously as the inspirational basis for building atomic weapons.
But resolving e=mc2 at the scale of sub-atomic particles – in equations called quantum chromodynamics – has been fiendishly difficult.
“Until now, this has been a hypothesis,” France’s National Centre for Scientific Research (CNRS) said proudly in a press release. “It has now been corroborated for the first time.”
For those keen to know more: the computations involve “envisioning space and time as part of a four-dimensional crystal lattice, with discrete points spaced along columns and rows.”
Einstein is still right on time
A precise test of time dilation confirms Einstein’s special theory of relativity. The results also provide important benchmarks for practical applications, such as the
PARIS: Particle accelerator experiments have provided the best test yet of Einstein’s special theory of relativity, proving that a moving clock ticks more slowly than a stationary one.
Time, as we all know, is relative: good experiences seem to fly by, whereas bad ones seem to drag on forever. “After two hours, I looked at my watch,” a reviewer of Wagnerian opera is said to have written. “I found that 17 minutes had gone by.”
In 1905, Albert Einstein wrote his own treatise on the relativity of time; famously theorising that time speeds up or slows down according to how fast an object is moving in relation to another object. Thus, according to his hypothesis, a clock that is in motion ticks more slowly than an identical clock, which is at rest – a phenomenon that Einstein called time dilation.
Theoretically, if one of two identical twins were launched into space, at very high speed, when he returned home he would be younger than his earthbound twin.
Atom beams
Now, as reported in the U.K. journal Nature Physics, the most accurate experiment yet into time dilation has proven the great German physicist to be bang on target.
An international team of researchers used a particle accelerator to whizz two beams of atoms around a doughnut-shaped course to represent Einstein’s faster-moving clocks. They then timed the beams using high-precision laser spectroscopy and found that, compared with the outside world, time for these atomic travellers did indeed slow down.
“We were able to determine the effect more precisely than ever before,” said lead researcher Gerald Gwinner of the University of Manitoba in Winnipeg, Canada. “We found the observed effect to be in complete agreement.”
The experiments, said Gwinner, confirm the technology aboard U.S. military satellites that provide the signals for the Global Positioning System (GPS) – the “satnav” network that is used as a navigational aid around the world. GPS satellites have precise atomic clocks on board in order to send out synchronised signals that are then transcribed by trigonometry to give one’s position.
Time dilation
“GPS uses satellites to measure the position of objects on the ground, but it needs to take into account the fact that the satellites themselves are in motion at high speeds as they orbit the Earth,” said Gwinner. “Our test validates the theory used by the devices to compensate for the satellites’ motion.”
The experiments took place at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, and include researchers from that organisation, the Max Planck Institute for Quantum Optics in Garching, and Mainz University.
The first measurement of Einstein’s time dilation took place in 1938, when U.S. scientists used the Doppler effect – the change in pitch when a sound and the person hearing it are moving apart or closer together – as the measuring tool.
Einstein’s theory of relativity has become the basis for innumerable science fiction tales, for it opens up the prospect of bending and distorting time.
