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Farthest confirmed galaxy is a prolific star creator

Hubble Space Telescope image of z8_GND_5296 — A long time ago in a galaxy far, far away: a Hubble image of a region in the northern sky, where nearly every object seen is a galaxy. The zoomed panel highlights z8_GND_5296, which is the most distant galaxy known to astronomers. (Courtesy: V Tilvi (Texas A&M), S Finkelstein (UT Austin), the CANDELS team and HST/NASA)

Astronomers in the US have measured the distance of the farthest known galaxy, finding that its light took 13.1 billion years to reach Earth – which means the light was emitted just 700 million years after the Big Bang. Although the galaxy is much smaller than the Milky Way, it is forming stars at a much faster rate. The discovery provides important new information about the epoch of reionization, the ancient era when the neutral gas between galaxies became ionized.

To observe the farthest galaxies, astronomers exploit the universe’s expansion, which stretches – or redshifts – the light waves of distant objects to longer, or redder, wavelengths. But dust can also redden light, so a red colour alone does not guarantee that a galaxy lies at the edge of the observable universe.

“The problem had been, over the previous few years, [that] people have been trying to confirm these really distant galaxies – and for the most part coming up empty,” says Steven Finkelstein, an astronomer at the University of Texas at Austin who was involved in the discovery.

Seeking faint spectra

Confirmation of a far-off galaxy’s distance requires measuring the redshift of lines in the spectrum of light that it emits. This means that astronomers face the challenge of obtaining the spectrum of a faint object. So for two nights in April, Finkelstein took aim at 43 red objects in the constellation Ursa Major with one of the largest telescopes in the world, the 10-metre Keck I telescope atop Mauna Kea in Hawaii. A year earlier, this telescope had received a more sensitive spectrograph, which made Finkelstein’s observations possible.

Finkelstein searched the spectra for a line from Lyman-alpha emission. This radiation arises when an electron falls from the n = 2 to the n = 1 state of hydrogen, which is the most abundant element in the cosmos. This spectral line normally emits far-ultraviolet radiation at a wavelength of 1216 Å (121.6 nm), but because of the hoped-for redshifts, Finkelstein obtained his spectra at near-infrared wavelengths instead.

Disappointment, then discovery

In 42 of the 43 spectra, Finkelstein saw no lines. “I was disappointed, I think – until I figured out the redshift of the one we did see and realized it was the most distant one.” That galaxy, bearing the unwieldy name z8_GND_5296, has a Lyman-alpha line at a wavelength of 10,343 Å (1.0343 μm), a 751% increase over the rest wavelength, which means that the galaxy’s redshift is 7.51. It is 40 million light-years more remote than the previous record holder, at redshift 7.215.

It’s a significant step in terms of distance and it’s a very unusual galaxy
Dominik Riechers, an astronomer at Cornell University

“That alone is remarkable,” says Dominik Riechers, an astronomer at Cornell University in Ithaca, New York, who was not part of the research team. “It’s a significant step in terms of distance, and it’s a very unusual galaxy.”

Because of its great distance, we see the galaxy as it was just 700 million years after the Big Bang. At that time galaxies were small because they had yet to grow larger. All the galaxy’s stars put together weigh only a billion times more than the Sun, a fraction of the Milky Way’s stellar mass.

But the galaxy is growing up fast. Its stars have already enriched it with heavy elements. Furthermore, it is undergoing a “starburst”: Finkelstein and his colleagues calculate that the galaxy converts about 330 solar masses of gas into stars each year – roughly 100 times the Milky Way’s rate. At that pace, the galaxy could have created all of its stars in only three million years.

Much too fast?

That’s much too fast for Abraham Loeb, who chairs the astronomy department at Harvard University. “The thing that makes me worried is that you really need the entire galaxy to be dense and synchronized” in order for it to make all its stars so quickly. Loeb says a group of galaxies might lie in front of the galaxy and gravitationally amplify its light, making it seem more prolific than it really is.

But Finkelstein says another distant galaxy, at redshift 7.21, is also a vigorous star creator. “We think that finding two of these in a relatively small region of the sky is telling us that in the early universe there are more sites of very intense star formation than we had previously thought possible,” he says.

In any event, the galaxy yields insight into the ancient universe. In particular, 700 million years after the Big Bang, at least some of the gas between the galaxies must have made the transition from neutral to ionized. Otherwise, Finkelstein would not have detected the galaxy’s Lyman-alpha radiation, because neutral hydrogen gas scatters it away. Indeed, that may be why he failed to find this radiation from other distant galaxies, some of which may be even farther away.

Alternatively, the galaxies themselves may be to blame. They may harbour so much neutral hydrogen gas that it traps all the Lyman-alpha radiation they generate. The starburst in the one galaxy whose distance Finkelstein measured might have blasted holes in the gas, so Lyman-alpha radiation could escape the galaxy and reach telescopes on Earth.

The astronomers report their discovery today in Nature.

From the dark universe to graphene

By James Dacey

In just over an hour’s time, I’ll be hopping on my bike and cycling to the top of a steep hill where the Nobel laureate Andre Geim will be found practising his lines. Sir Andre Geim is delivering a talk at the University of Bristol as part of a series of lectures to celebrate the 25th anniversary of Physics World. In Random Walk to Stockholm, Geim is going to be discussing his work on graphene that led to him sharing the 2010 Nobel prize with Konstantin Novoselov. He will also try to explain why this “wonder material” is attracting so much attention today.

For the small percentage of you who live close to Bristol, there are still tickets left for the event, which starts at 18:00 local time (by rippstein). I am planning to publish an audio recording of the lecture on this website after the event, for those of you who cannot attend tonight.

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Higgs MOOC sees spike in interest after Nobel

Peter Higgs and François Englert, — Peter Higgs (left) and François Englert, winners of the 2013 Nobel Prize for Physics. (Courtesy: Dirk Dahmer; CERN)

By James Dacey

The story goes that on the morning of this year’s Nobel Prize for Physics announcement, Peter Higgs had popped out for a leisurely lunch at a local pub without telling his colleagues at the University of Edinburgh. It meant that the Nobel prize committee in Stockholm was left scrabbling around trying to contact Higgs on several numbers, to no avail. We heard from François Englert in the slightly awkward phone conversation that customarily follows the prize announcement. But there was still no sign of the elusive Prof. Higgs.

Well fear not, because we will finally get to hear from the man behind the boson about his crowning achievement, via a free online course offered by the University of Edinburgh. The Discovery of the Higgs Boson is a seven-week course “about developments at the Large Hadron Collider, particle physics and understanding the universe”. Registration is already open for the massive open online course (MOOC), which starts on 10 February. It will feature interviews with Higgs himself and filmed lectures by a team of particle physicists at the University of Edinburgh, along with additional material including notes and further videos for more advanced students.

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CERN physicist picked for new UN panel

Four physicists have been appointed to a newly created panel that will advise the United Nations (UN) on scientific matters. The UN’s scientific advisory board – appointed by the UN secretary-general Ban Ki-moon – will feature 26 eminent scientists, including CERN particle physicist Fabiola Gianotti, who is the former spokesperson for the ATLAS experiment.

The idea for a science board originated from a recommendation in a January 2012 UN report – Resilient People, Resilient Planet: A Future Worth Choosing – that called for a “major global scientific initiative to strengthen the interface between policy and science”. The new board, which will offer expertise in a range of areas from medicine and plant breeding to engineering, is expected to provide advice on science, technology and innovation to the UN secretary-general and to the leaders of UN organizations. The UN Educational, Scientific and Cultural Organization (UNESCO) will host the secretariat for the board.

In a statement, UNESCO says that the new body will aim to “ensure that up-to-date and rigorous science is appropriately reflected in high-level policy discussions in the UN system” and will provide recommendations and advice on up-to-date scientific issues including on informing on issues related to the “public visibility and understanding of science”.

Joining the club

Three other physicists will join Gianotti on the panel. They include Susan Avery, president and director of the Woods Hole Oceanographic Institution in the US, Vladimir Fortov, who is president of the Russian Academy of Sciences, and nuclear physicist Dong-Pil Min from Seoul National University.

The 26-member panel also features two Nobel laureates including Ahmed Zewail from the California Institute of Technology, who won the 1999 Nobel Prize for Chemistry for his work in femtosecond spectroscopy. Zewail is joined by Ada Yonath, director of the Helen and Milton A Kimmelman Centre for Biomolecular Structure and Assembly at the Weizmann Institute of Sciences, who shared the 2009 Nobel Prize for Chemistry for her work on the structure and function of the ribosome – a key biological particle for the synthesis of proteins.

“It brings together scientists of international stature and will serve as a global reference point to improve links between science and public policies,” adds UNESCO director-general Irina Bokova.

Members of the UN science advisory board will be expected to act in their “personal capacity and will provide advice on a strictly independent basis”. The board members will serve for two years, with the possibility of renewal for one further two-year term. Gianotti told physicsworld.com that the role will be unpaid. “I don’t think these tasks should be remunerated,” she says.

The first meeting of the newly established board will take place at the start of 2014.

Pushy bacteria could shed light on tumour growth

Bacteria can colonize a vast number of surfaces in everyday life, from water pipes to teeth, spreading harmful disease in the process. Scientists had assumed that the growth of such colonies relies on bacteria being able to propel themselves towards sources of food, but a group of physicists in Scotland has now shown that colonies expand using nothing more than the simple mechanical repulsion between bacteria that takes place when they grow and bump into one another. This insight could improve our understanding of antibiotic resistance, say the researchers, and may even help in the fight against cancer.

Scientists use computer models of bacterial colonies to better understand a number of key characteristics of these ubiquitous structures. One parameter of great interest is a colony’s speed of growth because this determines how quickly disease can spread. Another important characteristic is a colony’s shape. Bacteria reproduce rapidly, which increases the possibility that they will mutate and acquire resistance to antibiotics. But reproduction requires nutrition and it is possible that the newly formed bacterium will be beaten by neighbouring cells in the race to reach the nutrients that are more abundant on the edge of the colony. The shape of the colony can dictate the outcome of that race.

According to existing models, which are based on a theory developed by biologist Ronald Fisher and mathematician Andrey Kolmogorov in the 1930s, the growth rate and shape of bacterial colonies depend on both a Brownian-motion-like diffusion of nutrients and a random but active motion on the part of the bacteria. However, these models fail to describe the behaviour of colonies growing on a surface, where bacteria are often unable to propel themselves.

Bacteria as ‘active matter’

In the latest work, Fred Farrell and colleagues at the University of Edinburgh, working with Oskar Hallatschek of the Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany, set out to establish the importance of mechanical forces in the growth of dense colonies of bacteria on solid substrates. Part of a growing number of physicists investigating “active matter” that exists far from thermal equilibrium, the team was also motivated by recent research showing that mechanical pressure can affect the growth and death rate of cells, including cancer cells.

The researchers model the evolution of non-self-propelling single-celled bacteria, starting with a single cell or a row of cells, which are surrounded by nutrients that they gradually deplete to grow and divide. Each bacterium is considered to be an elastic rod that grows along its length and which splits into two when it reaches a certain size. As it expands, the bacterium pushes against its nearest neighbours, creating movement by virtue of the elastic force between it and them.

The researchers found that this mechanical force pushes the colony outwards, allowing it to overcome surface friction. An increase in the strength of the pushing force leads to a faster growing colony. They also discovered that the shape the colony takes on as it expands depends on the ratio of the cells’ growth rate to the amount of nutrients available. When nutrition levels are low the colony forms branches to find more food, whereas with bountiful supplies the colony becomes circular, as is observed experimentally.

No diffusion needed

Contrary to the Fisher–Kolmogorov models, this behaviour was achieved without the diffusion of the bacteria and it also relied little on diffusion of the nutrients. Farrell’s colleague Bartek Waclaw points out that the results from the new model could be tested experimentally by confining a bacterial colony to 2D inside a microfluidic array and then imaging it to see how quickly it grows. Whereas the older models predict that the growth should be linear, the new one says it should either be slower than linear or exponential.

Having only two dimensions, however, the model’s utility will be limited, according to Waclaw. Although he adds that a basic 3D extension of the model does reproduce the main results. He explains that newly formed bacterial colonies can exist briefly as a single layer of cells, but colonies quickly build up successive layers. In addition, he points out, many bacteria exchange chemicals to communicate with each other and such signals are not incorporated in the current model. He says, however, that the model could mimic what happens at the early stages of the skin-cancer melanoma, which, he explains, starts out as an essentially flat colony of cells.

Looking at mutations

Waclaw adds that the group is now working on an extended version of the model that allows them to investigate directly how the mechanical properties of bacteria affect the rate of production of potentially antibiotic-resistant mutations. To do so the researchers assume that a certain fraction of the bacteria are mutant varieties and that these cells can grow a little faster than the rest. They then calculate the probability that a drug-resistant mutant cell can reach the nutrients ahead of its rivals and form a critical mass of cells.

A long-term aim of this research, says Waclaw, is to develop drugs that can control the mechanical properties of cells to lower the odds of those cells acquiring antibiotic resistance. “This is just a hypothesis,” he cautions, “but the ultimate hope is that it will one day be possible to modify mechanical interactions by applying a drug.”

The research is published in Physical Review Letters.

Physics World at 25: Puzzle 4

By Louise Mayor

Prepare to be perplexed by the fourth and penultimate brainteaser in the Physics World at 25 Puzzle. #PW25puzzle

Which food is, unusually, mentioned in the third of these well-known laws of physics?

KEPLcRS FIddT iAW ecYc hHec adu OrBug ey hVbit PLsNgm oS ff fjagnhf WenH bbg iUq sg Odh cF fme dfCv

egmyffa kijpNd vql DffmqszgS doW kHd garbtnpgmvbd dF kx nBJdCe xdLjcpe co uic McaS knD jHe FjRcE ACgecG ON IT

THE mmIRD LAW OF THERMODYNAMwCS GIVst xHe kNoRxPY iF nqsnx Ay kjMsivmTUio jjPnOACHlS ZERO

Surface plasmons reveal grain boundaries in graphene

Researchers in the US, Germany, Singapore and Spain have developed a new technique to obtain images of grain-boundary defects in graphene by analysing the behaviour of surface plasmons. Their study reveals that the defects act as electronic barriers and are responsible for the low electron mobility seen in some samples of graphene. The team also says that these barriers could find use as tuneable “plasmon reflectors” and “phase retarders” in plasmonic circuits of the future.

Graphene is a single atomic layer of carbon atoms that are arranged in a honeycomb lattice. It shows great promise for making electronic devices of the future thanks to its unique electronic and mechanical properties – which include extremely high electrical conductivity and exceptional strength.

A patchwork quilt

Defect-free graphene has the best mechanical and electronic properties but techniques for creating large, pristine graphene samples are limited by the emergence of grain-boundary defects. Much like the seams in a patchwork quilt, these defects form the boundaries between areas of perfect graphene. They are also notoriously difficult to characterize using conventional techniques such as transmission electron microscopy or optical microscopy.

The new nano-imaging technique developed by Dimitri Basov of the University of California at San Diego and colleagues was used to study graphene created by chemical vapour deposition (CVD) – a standard technique for making the material that suffers from grain-boundary problems.

Rippling across the surface

Surface plasmons are coherent wave-like oscillations of electrons that ripple across the surface of graphene and some other materials. In Basov’s experiment the plasmons are created by a nanoscale antenna – the metallic probe of an atomic force microscope – that is placed near the graphene surface and excited by infrared light (see figure). The plasmon waves are reflected and scattered by the graphene grain boundaries, creating interference patterns.

“By recording and analysing these interference patterns, we can map grain boundaries for large-area CVD films and probe the electronic and optical properties of individual grain boundaries at the same time,” explains team member Zhe Fei.

Charged line defects

The analyses show that grain boundaries in CVD-grown graphene are “charged line defects” that act as obstacles to both charge transport and plasmon propagation, he says. This discovery goes some way towards explaining why electrons travel slower in such graphene than in defect-free samples. On the other hand, grain boundaries might be exploited as plasmon reflectors and phase retarders – which are essential components for future graphene-based plasmonic circuits. Indeed, the team says that it is already looking at making such circuits by creating charge barriers in graphene that are similar in structure to grain boundaries.

Plasmon reflectors are used to change the path of plasmon waves in a material, in analogy to a mirror (or a beam splitter) in optics, explains Fei. Plasmon phase retarders are used to add phase delay to the plasmon waves, in analogy to an optical waveplate. “Our experiments indicate that the graphene electronic barriers themselves are plasmon reflectors and phase retarders and so can be used to reflect plasmon waves and also to add phase delay to the reflected waves.”

Shrinking optics

Controlling plasmons in this way could be particularly useful for shrinking the size of optical devices. This is because light can interact with surface plasmons to create waves called surface plasmon polaritons (SPPs), which have much shorter wavelengths than the original light. As a result, devices controlling SPPs can be much smaller than their optical counterparts.

The nano-imaging technique might also be used to analyse a variety of other materials in which plasmon waves exist, he adds. Such materials include metals, superconductors and topological insulators. It might even be extended to structures that support surface phonons waves (vibrations of the crystal lattice), such as dielectric materials, for example.

“The electronic properties of a grain boundary are largely related to its atomic structure so we will now be correlating our technique with an atomic-scale method such as scanning tunnelling microscopy, to study grain boundaries,” says Fei. “Such studies will help us better understand the exact relationship between structure and properties of these defects.”

The research is reported in Nature Nanotechnology 10.1038/nnano.2013.197.

This article first appeared on nanotechweb.org

3D printing, Ada Lovelace and controversial bloggers

By James Dacey

One of the more inspiring stories we have come across this week was the tale of a resourceful inventor in the West African nation of Togo. Kodjo Afate Gnikou has managed to build a 3D printer at the meagre cost of $100 by mainly using parts he found in a scrap yard in the capital city Lomé. The story is described on inhabitat.com, which says the machine has been constructed from broken scanners, computers, printers and other e-waste.

On the subject of 3D printing, Wired magazine ran a story about how the UK supermarket chain Asda is planning to trial a 3D printing service at its store in York. They will be offering customers the chance to take a break from their shopping to have a full body scan, which will be used to create miniature dolls of themselves. Prices apparently start at £40 and Asda boasts about how lifelike these dolls can be: “The technology produces highly realistic ‘mini me’ figurines at whatever scale you like!”

From a shop in York to the next story that involved celebrations all round the world. Tuesday was Ada Lovelace Day 2013. The annual celebrations, which are now in their fifth year, are held to recognize the achievements of women in science, technology, engineering and maths (STEM). The annual event was founded in 2009 by the social technologist and writer Suw Charman-Anderson “as a response to online discussions about the lack of women on stage at tech conferences”.

This year events included a mass Wikipedia “editathon” at the University of Oxford in an attempt to raise the profile of women’s contributions to science, as described in this article in the Guardian.

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Astronomers discover furthest gravitational lens

The most distant gravitational lens yet has been found at a colossal distance of 9.4 billion light-years. The chance discovery by an international team of astronomers not only allowed the team to directly measure the mass of the distant galaxy that caused the lensing but has also led to questions about the more distant object whose light was lensed. The magnified object is a type of dwarf galaxy that is thought to be rare and the chances that such a peculiar galaxy would be gravitationally lensed are small. Therefore its observation suggests that current theories have underestimated the number of such galaxies in the early universe.

A gravitational lens is a large galaxy or group of galaxies that bends or “lenses” light from a distant source as it travels towards an observer. The effect was predicted by Einstein’s general theory of relativity. In rare cases the lens, the distant light source and the observer line up precisely and the result is an “Einstein ring” – a perfect circle of light around the lensing mass. However, if there is any misalignment along the way, astronomers observe partial arcs, spots and other such distorted images, depending on the relative positions of the bodies.

Useful rings

Such a lensing effect has proved to be useful – researchers can determine the mass of the lensing galaxy including its dark matter content – thanks to the amount of distortion or lensing observed. The lensing effect also acts as a “natural telescope” of sorts, magnifying details of distant galaxies that would be difficult to observe otherwise. Indeed, ever since the first evidence of such lensing was seen in 1979, astronomers and cosmologists have used the phenomenon to find distant objects and supernovae and to even map the dark-matter content of our universe.

Now, a team led by Arjen van der Wel from the Max Planck Institute for Astronomy in Heidelberg, Germany, along with colleagues in Italy and the US, has, rather accidently, detected the furthest such lens. Van der Wel was reviewing observations made with the Large Binocular Telescope in Arizona that were part of another study that looked at the spectra of massive, old galaxies.”[I] noticed a galaxy that was decidedly odd. It looked like an extremely young galaxy, and at an even larger distance than I was aiming for,” says Van der Wel. Intrigued by the anomalous object, he looked at other images of the object taken with the Hubble Space Telescope as part of the CANDELS and COSMOS surveys and once more the object looked like an old galaxy but with some irregular features. As a result, Van der Wel suspected that he might be looking at a gravitational lens. He combined all the available images of the object and corrected for the haze of the lensing galaxy’s stars to see a “quadruple lens” that formed an almost perfect Einstein ring.

The researchers found that after being deflected, light from the lens travelled nearly 9.4 billion years to reach us, corresponding to a redshift of z = 1.53. This puts the lens much further away than other lenses discovered to date. From the amount of distortion observed, the researchers calculated that the lens galaxy has a total mass of 8 × 10¹⁰ solar mass. From that, nearly 75% of this is made up of stars, meaning that the rest of the mass could consist of dark matter. But Van der Wel explains that uncertainties are such that all mass in the lens can be accounted for by stars only.

Hitting the bullseye

Seeing an Einstein ring also means that both the lens and the background light source are aligned to better than 0.01 arcseconds – that is equivalent to a 1 mm separation at a distance of 20 km. Van der Wel tells physicsworld.com that this was indeed a rare alignment – “If the light rays are darts thrown in New York City, then they managed to hit the bullseye of a dartboard in Boston. Now, the universe throws many darts around (there are many background galaxies) and has many dartboards (many potential foreground lenses), but not that many. The chances of hitting a dartboard are not so small, but the chances of hitting the bullseye…” exclaims Van der Wel.

But the distance and fortuitous alignment were not the only surprises from this study. The background light-source galaxy (even more distant at z = 3.41) itself proved to be a “star-bursting dwarf galaxy”. This is a comparatively low-mass galaxy (only about 100 million solar mass worth of stars) that is extremely young (only about 10–40 million years old) and produces new stars at an enormous rate. Such dwarf starburst galaxies are thought to be rare and the chance of these peculiar galaxies being lensed is small. Yet this is the second starbursting dwarf galaxy found to be lensed. This might force astronomers to re-think their models of galaxy evolution as starbursting dwarf galaxies might be much more common than previously thought. “Perhaps only one in a hundred faint galaxies is a starbursting dwarf galaxy. That combined with the chance alignment makes this a very unlikely object,” says Van der Wel.

The research is to be published in Astrophysical Journal Letters. A preprint is available on arXiv.

Laser accelerator breaks the gigaelectronvolt barrier

Schematic showing the laser passing through the two gas jets.
(Courtesy: Hyung Taek Kim *et al.* *Phys. Rev. Lett.* **111** 165002)

By Hamish Johnston

There is an interesting paper in Physical Review Letters this week with the mouthful of a title: “Enhancement of electron energy to the multi-GeV regime by a dual-stage laser-wakefield accelerator pumped by petawatt laser pulses“. This piqued my interest because I recently wrote an article for the 25th anniversary issue of Physics World that looks at how laser acceleration of protons and other hadrons could make certain cancer therapies more accessible.

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