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Flash Physics: Newborn stars collide, wind creates rogue waves, ion-trap pioneer Hans Dehmelt dies

Newborn stars collide in a cosmic firework

The explosive collision of newly born stars has been captured by astronomers in unprecedented detail. John Bally of the University of Colorado Boulder in the US and colleagues used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe the Orion Molecular Cloud 1 (OMC-1), located within the constellation of Orion 1350 light-years away. OMC-1 is an active star-formation factory – a massive, dense cloud of gas. As it collapses under its own gravity, OMC-1 produces stars and – in the densest regions of the cloud – protostars. Astronomers suggest that several protostars began to form about 100,000 years ago and, before they could escape their stellar nursery, gravity started to pull them together. A mere 500 years ago, two of the protostars collided, producing a dramatic and powerful explosion with as much energy as the Sun emits in 10 million years. The collision caused gas, dust and the other nearby protostars to be propelled out into space at over 150 km/s. The resulting cosmic firework in OMC-1 was first observed in 2009, but the latest high-resolution ALMA images have revealed details about the distribution and motion of carbon monoxide within the streamers. The results, published in the Astrophysical Journal, may provide greater understanding of how such events impact star formation. It is thought that although protostar collisions are relatively short-lived (lasting only centuries), they are probably fairly common and may regulate stellar formation in massive molecular clouds.

Wind creates rogue waves in the lab

Wind-driven rogue waves have been created in an experimental water tank for the first time. Rogue waves are huge walls of water that can emerge without warning on a relatively calm ocean. Long a part of seafaring lore, it has only been very recently that physicists have begun to study these dramatic events. Previous studies used paddles to create rogue waves in water tanks, and have shown that they can occur as a result of nonlinear self-focusing of smaller waves. However, ocean waves are created by the wind, and so these paddle-driven rogue waves may not offer a realistic model of the phenomenon. Now, an international team led by Alessandro Toffoli at the University of Melbourne in Australia has looked at the more realistic role of wind in rogue-wave formation using an annular water tank. The tank has an outside diameter of 5 m, an inside diameter of 1 m and a depth of 46 cm. Turbines drive the water around the tank and two large fans create a wind blowing over the surface at 16 km/h. The circular flow eliminates an important limitation of wind studies in linear wave tanks – the tanks are too short for wind-blown rogue waves to emerge. With water and air flowing in a circle, the distance that the wind travels over the water is essentially unlimited. After switching the experiment on, it takes about 30 min for that tank to reach a stable state in which most of the waves are about 5 cm tall. However, the team also observed rogue waves that were about 2.2 times higher than the stable waves. Most of the rogue waves appeared just before the tank reached the stable state. In general, taller than average waves became more common in the tank at this time – with their frequency falling after the steady state was reached. This suggests that strong nonlinear interactions are present in the tank at that time, affirming the findings of previous studies. The study is described in Physical Review Letters.

Ion-trap pioneer Hans Dehmelt dies at 94

Photograph of Hans Dehmelt
Hans Dehmelt: 1922–2017. (Courtesy: University of Washington)

Hans Dehmelt, the German-born US physicist who shared the 1989 Nobel Prize for Physics for the development of ion traps, has died at the age of 94. Dehmelt was born in Germany in 1922 and gained a Master’s degree in physics in 1948 and a PhD in 1950 from the University of Göttingen. In 1952 he then went to Duke University in the US, before moving to the University of Washington in 1955, where he remained for the rest of his career until retiring in 2002. It was during his time in the US that Dehmelt developed the Penning trap that used magnetic and electric fields to trap ions and electrons, allowing them to be studied to high precision. Today, such traps are used to study to properties of antimatter, such as antihydrogen. For this breakthrough, Dehmelt shared half the 1989 Nobel prize together with Wolfgang Paul from the University of Bonn, while US physicist Norman Ramsey was awarded the other half for his work probing the structure of atoms to high precision.

 

  • You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics.

Once a physicist: Z Aziza Baccouche

Aziza Baccouche
(Courtesy: Aziza Productions)

What sparked your interest in physics?

I’ve always had a passion for maths, but I lost most of my sight when I was nine years old. I grew up in Tunisia and went to a blind school there for a few years before my parents decided to come back to the US. My mom is African-American and my dad is from Tunisia. When we came to the US, I went to a regular high school and in my senior year I took physics and immediately fell in love with the subject. I had a fantastic teacher who never saw my physical limitations in terms of my sight. He never said “Oh no you can’t do this lab,” or “You shouldn’t do physics,” and this was crucial. I was a young person and I knew I would have to prove myself as a legally blind person.

What were some of the challenges you faced as a blind person in physics?

It was when I went to the College of William and Mary in Virginia to study physics that I really encountered difficulties. For the first time I found it tough trying to make my coursework accessible to me. I was the first blind person to study physics there so the books weren’t on tape, I had to find readers to record the coursework. There seemed to be all of these issues that I had to worry about that my colleagues didn’t even think about. This puts you a little behind. My peers could just pick up a book or go to the library to get information while I didn’t have that flexibility. As I would be listening to audio, something like turning back to page 10 wasn’t as easy for me as it was for a sighted person. This forced me to memorize as much as I could. I would memorize all the formulae and equations and in the long term this made physics easier for me. I think the biggest thing though was dealing with other people’s perceptions about what blind people can and can’t do. The first thing that people see is my disability. After that, they notice that I am a woman and also African-American so it’s like a three-strike situation. This was the reality, especially as I was in a predominantly white male department, so it was really hard for me to feel like I belonged. But I had a drive that came from within me – an ability to envision possibility.

How did you get into media and films?

When I was doing my PhD at the University of Maryland I applied for an American Physical Society Mass Media Fellowship, and when I got it, it was the most fantastic experience. They assigned me to CNN in Atlanta. Although the programme was meant to be only 10 weeks, I ended up doing more than three months and I even took a semester off my PhD because I wanted to focus on the fellowship. I had the opportunity to learn all about science communication and I found that I was really interested in the media. People often assume that as a blind person, you would not want to be in front of the camera, but that was what interested me most, along with producing media content. My time at CNN was great and I even got to meet then chief executive Tom Johnson. He was on the advisory board of the School of Journalism in Maryland and he took me under his wing. When the fellowship ended I continued to produce out of the Washington bureau, where I was a special science correspondent. I was the first blind on-air producer for the network and I really wanted to show that it didn’t take sight to do this. Who cares if my eyes don’t align properly to the camera lens – you should be paying attention to the content I am delivering. I then set up Aziza Productions, making short films for science-based non-profit organizations and focusing on minority communities in science.

Was it hard finding work after your fellowship?

As blind people we have to be part of changing the attitude that the general public has about us. Even today in the US, 70% of working-age blind people are unemployed. This is something I dealt with when I came out of my PhD and was trying to find work. You may have the credentials and the necessary skills and experience, but unfortunately people just see the blindness. There are many environments where people aren’t used to seeing blind people – physics was one and television was another. People think that it takes vision to do the work, but you could say that about any job. For me vision is a mindset, an attitude, and for that I don’t need sight. Of course it has been challenging and there have been roadblocks, but I have managed just fine without sight. I hope that my story inspires others with disability, especially in physics. The main barrier is dealing with people, not doing the physics.

How has your physics background been helpful in your media work?

I’m passionate about science and I love talking about it. My physics training helps me better communicate it because you have to understand it in order to effectively explain it to the general public. I also love working with people and storytelling, so journalism was an obvious path, but science was my first love.

What are you working on now?

I’m working on a documentary film called Seeking Vision. It’s about overcoming odds and not being able to see with your eyes. A little over 10 years ago I had my fifth brain operation and because I knew I wanted to produce a film that will connect with people, I had my camera crew in the operating room filming for nearly three hours of a seven-hour surgery. Although the hospital was worried about liabilities, my neurosurgeons allowed it. I want to show the reality of being blind and that we can do more than answer phones.

Do you have any advice for today’s students, especially those with any disabilities?

I like referring to the concept of disabilities as “different abilities”. I tell my sighted colleagues that while they see with their eyes, I do the same with my fingers while reading braille and with my ears while listening to audio. What drives me is my vision and my goals, both of which come from within. It’s important to know who you are and what you are capable of, so hold on to that vision.

LEGO acoustics, potato cannons go to war, personal politics and popular science

By Hamish Johnston

In the above video Brian Anderson of Brigham Young University shows how the acoustic concept of “time reversal” can be used to knock over a series of LEGO figures using sound. The idea is that sound waves are broadcast into an environment and captured by a sensor at a specific location. The signal is then used to work-out how the sound waves bounced about before reaching the location and this information is then used to target that specific location with subsequent sound waves. In the demonstration, sound knocks over 29 LEGO figures one-by-one. It’s very impressive and entertaining as well.

(more…)

Bell correlations measured in 500,000 atoms

Bell correlations – a hallmark of an entangled quantum system – have been spotted in an ensemble of 500,000 rubidium-87 atoms. The atoms were prepared in spin-squeezed states by physicists at Stanford University in the US and the correlations measured to a whopping statistical significance of 124σ.

In quantum mechanics, entangled particles have much stronger correlations than are allowed in classical physics – a property that can be exploited in quantum technologies including cryptography. In 1964 the physicist John Bell famously calculated an upper limit on how strong these correlations could be if they were caused by classical physics alone – what has become known as Bell’s inequality. Correlations stronger than this limit, Bell reasoned, could occur only if the particles are entangled.

In this latest work, Onur Hosten, Mark Kasevich and colleagues have measured these strong Bell correlations in an ensemble of 500,000 cold rubidium-87 atoms that are trapped by laser light. The atoms are put into an entangled state using a process called spin squeezing. The uncertainty principle dictates that the uncertainty in a measurement of the z-component of the total spin of the system multiplied by the uncertainty in the y-component must be larger than a certain value. Reducing (or squeezing) the uncertainty of the z-component increases the uncertainty of y-component, putting the system into a spin-squeezed state.

Not a fluke

It turns out that the technique used by Hosten and colleagues to create a spin-squeezed state in their atomic system also puts the atoms into an entangled state. The team then characterized this state by measuring two quantities. One is related to the total spin of the atoms in the z direction and the other is related to the total spin of the atoms in a direction n, which is in the z–x plane. Correlations between these two quantities can be expressed in terms of a Bell-like inequality. The team found that for certain values of n, the inequality was violated – showing that entanglement is present in the system. For some values of n, the statistical significance of the violation was 124σ, making it extremely unlikely that the measurement was a random fluke.

Kai Bongs of the University of Birmingham in the UK describes the work as “a very nice experiment done on a fantastic system”, and points out that the Stanford team has taken the atomic ensemble “deep into the quantum domain”. However, Bongs, who works in the field of quantum sensors, says that practical applications of the Bell correlation measurements are not obvious. Hosten concurs: “We do not know any immediate practical applications of the Bell correlation measurements. However the spin-squeezed states have immediate applications in improving the precision of atomic clocks and atom interferometers.”

Hosten points out that the team’s study differs from conventional Bell experiments because it does not look at correlations between measurements made at two different places. If the system could be adapted for atom interferometry – whereby the atoms can follow two different paths – it could be used to further test the predictions of quantum theory. The measurements are described in Physical Review Letters.

Leukosomes engage stealth mode by altering their protein shell

Leukosomes are a promising new type of nanoparticle for use in targeted drug and gene delivery. Preloaded with leukocyte proteins, the particles cloak themselves in a shroud of host protein. Researchers from the Houston Methodist Research Institute in Texas have investigated this coating to find out how they evade the host immune system.

Reaching your target behind enemy lines is easier if you can steal a uniform. Leukosomes are biomimetic lipid vesicles (liposomes) that are preloaded with host white blood cell proteins on their surface. When inside the body, they shroud themselves in host protein to slip past the immune system: it is this unknown shroud of host protein that makes them special.

When Ennio Tasciotti and colleagues in Texas and Italy compared how coated leukosomes and bare liposomes fared in the blood, they found that the liposomes were quickly swallowed up by the host immune system, whereas the leukosomes circulated far longer. In addition, the leukosomes reached sites of inflammation in greater numbers.

The researchers studied leukosomes sized from 80 to 1000 nm that coat themselves in a specific array of plasma proteins – a corona, which helps to conceal them from the deadly host immune system. This was what they investigated to find out how it might enable the stealth function of these vesicles.

Stealth mode

Tasciotti and colleagues imaged the leukosomes in mice by intra-vital microscopy. They found that the leukosomes were able to target inflamed tissue, while also circulating for longer in the blood. Moreover, the leukosomes had the ability to resist being swallowed by roaming phagocytic macrophages. In contrast, liposomes – while they did also pick up a protein corona – were more evenly spread from their point of origin and were quickly swallowed up. This induced ability to both turn on stealth mode and target specific organs was quite unexpected. Especially after the researchers analysed the protein corona and found that leukosomes adsorb fewer proteins to their surface than plain liposomes.

The final experiment of the paper seems to posit an answer: macrophage receptors. One possibility, the researchers argue, is that the macrophage receptors in the leukosome undergo receptor site–ligand binding with proteins in the blood. This effectively blocks the sites that macrophages would normally grab on to, so the leukosome goes on unimpeded.

Biomimetic particles like these have been described as Trojan horses, and were originally designed using erythrocyte membranes. Here, researchers have begun to characterize the corona – the “cloak of many colours” – an extra layer composed of hundreds of proteins that a leukosome takes on when it enters the blood of the host. Understanding this process might well help to make more bespoke, generally targeted nanoparticles, which can sneak through the immune system to deliver their precious cargo to a specific target.

Full details reported in ACS Nano.

Flash Physics: Superconductor is flexible, girls underestimate maths ability, super-Earth has atmosphere

Superconducting fabric is ultrathin, flexible and lightweight

A flexible fabric woven from plastic fibres and high-temperature superconductor nanowires has been unveiled by Uwe Hartmann, Volker Presser and colleagues at the University of Saarland in Germany. Potential applications of the material include coatings that screen objects form electromagnetic fields, flexible resistance-free electrical cables and friction-free motion through magnetic levitation. The material, which looks like charred paper, is a superconductor below about 73 K. However, unlike most other high-temperature superconductors – which are ceramics – the fabric is as flexible as plastic kitchen film. It has a density of just 0.05 g/cm3, which is just 1% of most supercomputing materials. “This makes the material very promising for all those applications where weight is an issue, such as in space technology,” says Hartmann, adding: “There are also potential applications in medical technology.” The superconducting nanowires are 300 nm or less in diameter and are made from yttrium-barium-copper-oxide or a similar material. The nanowire manufacturing process is described in Superconductor Science and Technology and the new material will be presented at the Hannover Messe industrial fair on 24–28 April.

Girls underestimate their mathematical ability, reveals study

Photograph of Lara Perez-Felkner
Confidence booster: Lara Perez-Felkner has found that girls underestimate their mathematical ability. (Courtesy: Florida State University)

A study by psychologists in the US has found that high-school girls rate their competence in mathematics lower than boys, even for those with similar abilities, according to research reported in Frontiers in Psychology. Carried out by Lara Perez-Felkner at Florida State University and colleagues, the study asked high-school students in the 10th and 12th grade to indicate their level of agreement to statements such as “I am certain I can understand the most difficult material presented in math texts”. For boys and girls who showed a high ability in mathematics, the researchers found that boys rated their ability 27% higher than girls. The authors say that this difference could explain why more boys go on to study mathematics and science at degree level and beyond. “The argument continues to be made that gender differences in the hard sciences is all about ability,” says Perez-Felkner. “But when we hold tests scores constant, we see boys still rate their ability higher, and girls rate their ability lower.” The authors suggest that initiatives such as regular science camps, extracurricular activity in science and increased access to female scientists could help to boost girls’ confidence in mathematics and science.

Super-Earth exoplanet has atmosphere

Artist's impression of GJ 1132b orbiting its host red dwarf
Steamy atmosphere: super-Earth may have atmosphere rich in water and methane. Artist’s impression of GJ 1132b orbiting its host red dwarf. (Courtesy: Max Plank Institute of Astronomy)

An atmosphere has been detected on an exoplanet that is slightly larger than Earth. Previous observations of atmospheres on planets outside the solar system have involved objects much more massive than Earth. But this is the first time an atmosphere has been detected on a planet only marginally bigger than ours – 1.6 times the mass of Earth and 1.4 times the radius. The planet in question, GJ 1132b, orbits a red-dwarf star 39 light-years away and is classified as a super-Earth because it is bigger than Earth but smaller than a gas giant. A European collaboration used the GROND imager at the MPG/ESO 2.2 m telescope of the European Southern Observatory in Chile to image the changing brightness of GJ 1132b’s host star as the planet passed in front of it. By looking at seven different wavelengths, the team saw that the planet appeared bigger when observed in the infrared. This suggests that GJ 1132b has an atmosphere that is opaque to infrared but transparent to other wavelengths. Using simulations, the researchers suggest this is because the atmosphere may be rich in oxygen and methane, but with the current data it is not possible to say how similar or dissimilar GJ 1132b is to Earth. It may be a water planet with a steam atmosphere, for example. Meanwhile, as the current method for detecting life on other planets is to look for fingerprint chemical imbalances in their atmospheres, the finding, published in the Astronomical Journal, is a step towards finding life outside the solar system.

 

  • You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on Belle correlations between 500,000 atoms.

Soliton molecules dance in a kaleidoscope of light

Illustration of soliton molecules
Molecules on the move: illustration of soliton molecules. (Courtesy: Claus Ropers)

Solitons – non-dispersive wavepackets – are key features of nonlinear optics and other nonlinear wave systems. Theoreticians have long predicted that solitons can bind together to form “molecules” – and experiments have confirmed this in simple cases. Now, researchers in Germany and the US have analysed the spectra of soliton molecules multiple times as they ricocheted between the mirrors of a laser cavity – gaining remarkable insights into the dynamics of pairs and even triplets of solitons.

Light in optical fibres normally behaves as the linear sum of its frequency components. Laser pulses therefore gradually spread out as different frequencies travel at different speeds in a fibre. At high powers, however, the refractive index of glass fibre becomes nonlinear, so higher-intensity pulses propagate more slowly. This acts to push pulses together and, under specific conditions, the two effects can balance each other to create solitons – waves that travel forever without dispersing.

These nonlinear effects can also allow different light pulses to influence each other. “You have two balanced pulses that, when they come into each other’s sphere of influence, start bouncing off each other like lightsabers!” says Claus Ropers of the University of Göttingen. Under some conditions, they can also form bound states.

Relative motion

Soliton molecules have been previously observed in laser cavities, but only when the pulses moved in lockstep. “If you have two soliton pulses that are circulating stably in a cavity, you can see that simply from the optical spectrum of the laser,” explains Ropers. Decades of simulations have suggested this scenario, with pulses moving stably, is a subset of a much broader, richer range of mathematically possible soliton dynamics. However, soliton pairs in constant relative motion had never previously been observed in real time.

“Once the solitons start moving, the optical spectrum of the laser is completely washed out,” says Ropers, “You don’t see anything. Basically, you need to measure the optical spectrum of every laser shot.” With the solitons bouncing back and forth at the speed of light, however, this is a near-impossible task.

In the new research, Ropers and colleagues at the University of Göttingen and the University of California, Los Angeles, developed an ingenious and relatively simple technique they call “real-time spectral interferometry”. Each time the solitons bounce against the partial mirror of their laser cavity, a small proportion of the light escapes down a kilometre-long optical fibre. “This very little extracted energy doesn’t have enough intensity to create nonlinear effects in the fibre, so [the pulses] just see the dispersion,” explains team member George Herink. “The pulses therefore disperse in time until they overlap. When they overlap they interfere, and then the spectral patterns encode the original timing.” This allowed the team to capture a movie of soliton evolution with a shutter speed of just a few nanoseconds.

High-power triplets

The researchers first created two solitons in an optical cavity and manoeuvred them closer until they formed a static bound state. They also looked at solitons with fixed relative positions, but with a continually evolving relative phase. Soliton pairs whose relative positions changed continuously were also made, as Herink explains: “The first pulse is more intense, so it runs a bit slower because of the nonlinear refractive index. The second pulse therefore catches up: when they get close enough, another nonlinear effect makes them repel again. This kind of stuff can happen continuously, and what we see in our data is two pulses continuously changing their distance.” The team also observed soliton triplets at very high powers, and found that, when they turned the power down slightly, the triplet became a pair of solitons.

The researchers now intend to investigate their solitons in more detail. “This work is a kaleidoscope of the phenomena that you can actually see,” says Ropers. “We describe a range of different solutions, but there’s a lot more in terms of the physics of this and what exactly causes these dynamics.” He says this set-up acts as an “analogue simulator” of soliton dynamics, which appear in many other physical systems, some of which – such as Bose–Einstein condensates in ultracold gases – are much harder to investigate experimentally. Beyond this, Herink says that, if the researchers can control the evolution of the time lag between two pulses, this could be useful to chemists using pump-probe spectroscopy to follow ultrafast reaction dynamics.

The research is described in Science.

Researchers see inside integrated circuits at high resolution

The 3D render of a detector chip obtained via the new X-ray process. Credit: Nature
The 3D render of a detector chip obtained via the new X-ray process. Credit: Nature

As the scale of integrated circuits (ICs) continues to shrink, the lack of practical methods for imaging their complex internal structure has hampered feedback for quality control and product development. A collaboration led by Mirko Holler at the Paul Scherrer Institut in Switzerland has published work in Nature that shows how X-rays can be used to produce 3D renderings of the internal structure of ICs with resolutions as low as 14.6 nm in all three dimensions.

Modern ICs are highly complex structures with feature sizes well below 100 nm and multiple layers of silicon, metals and silicon dioxide. Making these tiny devices is a mammoth engineering challenge, but another surprising problem faced by IC manufacturers is the ability to see what they have actually made. The current options for high-resolution imaging are atomic force microscopy, which is a surface technique and electron microscopy methods, which have a penetration depth of only a few nanometres. Seeing inside ICs currently relies on the laborious and destructive process of sectioning the device with an ion beam and imaging each layer with scanning electron microscopy.

To overcome this problem, Holler’s team in Switzerland demonstrated an innovative approach using X-rays that can build a high-resolution 3D model of an IC’s internal structure. A coherent X-ray beam penetrates the sample and produces a diffraction pattern. They moved each sample to obtain several hundred such patterns, which are combined to produce a 3D model by a process known as tomography. The researchers used the so-called ptychographic scan method to obtain the diffraction patterns. This method takes 2 dimensional scans of the sample perpendicular to the X-ray beam. By using overlapping scan positions it allows the phase of the x-rays to be determined, which produces higher resolution images than is normally achievable.

Drawbacks and limitations

Although the imaging method itself is completely non-destructive, the implementations presented by the collaboration still require a destructive sample preparation process. The first example requires access to a small sample from all angles. Holler and his team achieved this by cutting out an 11 µm cylindrical pillar from the chip. However, the researchers believe that whole chips could be imaged using laminography instead of tomography. This method forms a 3D image in a series of planes by collecting diffraction patterns through the sample, thereby needing access for the X-ray sources and detectors only from above and below. To achieve this for a complete off-the-shelf chip would require a higher power X-ray source than the researchers had available. Currently, there is also a lack of scanning instruments for the method.

A schematic of the set-up required for full-field laminography based on laboratory sources. Credit: S Gondrom et al; X-ray computed laminography: an approach of computed tomography for applications with limited access; Nuclear Engineering and Design; 190 (1–2) 141-147; 1999 http://dx.doi.org/10.1016/S0029-5493(98)00319-7.
A schematic of the set-up required for full-field laminography based on laboratory sources. Credit: S Gondrom et al; X-ray computed laminography: an approach of computed tomography for applications with limited access; Nuclear Engineering and Design; 190 (1–2) 141-147; 1999 http://dx.doi.org/10.1016/S0029-5493(98)00319-7.

The other major drawback to the method is imaging speed, as a practical method must be able to image whole chips in reasonable timescales. The current system can image a 5 µm square region in just under a minute, but anticipated advances in synchrotron radiation sources and X-ray optics suggest that a 0.5 mm square region will soon be possible in the same imaging time. Synchrotron sources are available in all areas with significant IC industries, but do impose a high cost. These costs however, are considered comparable to alternative imaging methods – such as transmission electron microscopy – as well as being potentially more powerful.

The team has managed to achieve non-destructive imaging of the internal structure of an IC with excellent 3D resolution. With further development of X-ray sources and optics this promises to be a transformative technology for the analysis and quality control of integrated circuits.

Exploring the worlds of TRAPPIST-1

Just 40 light-years from Earth, TRAPPIST-1 is relatively small compared with the size of our Sun, with a mass 80 times that of Jupiter. Researchers were able to spot periodic drops in intensity of light from the star, as observed by the TRAPPIST telescope in Chile. Using the “transit” method of exoplanet detection, the astrophysicists were able to infer the presence of seven planets sweeping across the face of the star. Remarkably, all seven objects appear to be similar in size to Earth, with radii ranging from 0.77–1.13 Earth radii. The team was able to determine the mass and density of six of the exoplanets, which suggests that they have rocky compositions.

In this podcast, Glester meets researchers involved in the discovery to find out what they know so far about the system. What would it be like to stand on the surface of a TRAPPIST-1 planet and stare out at the night sky? What is the geology of the planets? How can future space missions enable us to learn more about the system?

With his characteristic enthusiasm, Glester discovers that these planets could be even more intriguing than we first thought. You can also hear Glester’s extended conversation with lead researcher Michael Gillon on the Cosmic Shed podcast .

Flash Physics: EHT begins black-hole imaging, nanoparticles help polymers flow, double-beta decay not found

Worldwide telescope attempts to image a black hole

An attempt to obtain the first ever image of the Milky Way’s supermassive black hole has begun. The Earth-sized Event Horizon Telescope (EHT) has launched a 10 day run to obtain the portrait via very-long-baseline interferometry (VLBI). The telescope comprises eight radio dishes across the globe, including the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the South Pole Telescope (SPT) in Antarctica, and the IRAM 30 metre telescope in Spain. Since its first measurements in 2007, the EHT has yielded tantalizing results even without the full array of telescopes. Now, all eight are linked and looking at our black hole, Sagittarius A* (Sgr A*), as well as the even bigger one in the neighbouring galaxy M87. Although black holes are inherently invisible because of their extreme density and gravitational field, the researchers hope to image the point where matter and energy can no longer escape – the so-called event horizon. “This week heralds an exciting and challenging endeavour for astronomy,” says France Córdova, director of the funding agency National Science Foundation. For more information on the EHT, see our feature “Portrait of a black hole“.

Nanoparticles help molten polymers flow

The addition of tiny particles to a molten polymer can help the material to flow more easily, according to a study led by Erkan Senses and Antonio Faraone of NIST and the University of Maryland in the US. This comes as a surprise because normally the addition of nanoparticles to a polymer results in a reduction of flow. Polymer materials comprise long strand-like components that entangle together to form familiar materials such as plastics. Melting polymers so that they can be moulded and extruded plays an important role in manufacturing. However, the entangled nature makes it difficult for some molten polymers to flow. Senses and Faraone added gold particles just 3 nm in diameter to the polymer polyethylene oxide. Using a number of different analysis techniques, the team showed that the viscosity of the mixture was lower than that of pure polyethylene oxide. The nanoparticles are smaller than the gaps between the entangled strands, and by settling into these gaps, the team believes that the nanoparticles are able to push the strands apart and cause the molten polymer to flow more freely. The team also looked at what happened when 20 nm particles are introduced. These are larger than the gaps between the strands and they had the opposite effect of reducing the viscosity. The research is described in Physical Review Letters.

“Background-free” neutrinoless double-beta decay search comes up cold

GERDA – an array of semiconductor detectors immersed in a bath of liquid argon – has failed to see any evidence for neutrinoless double-beta decay. Neutrinoless double-beta decay is a hypothetical process whereby two neutrons in a nucleus decay to two protons and two electrons – but no neutrinos. Expected to be extremely rare, this decay process is only possible if the neutrino is its own antiparticle – a Majorana particle – which is a feature of some extensions to the Standard Model of particle physics. Measuring neutrinoless double-beta decay would provide important information about the masses of neutrinos – physicists know the particles have mass, but not what the masses of different types of neutrinos are. One of the few nuclei that could possibly undergo neutrinoless double-beta decay is the naturally occurring isotope germanium-76. GERDA takes advantage of the fact that germanium can be used to create very good radiation detectors. Neutrinoless double-beta decay would produce two electrons within a germanium detector, which creates two pulses of positive charge that are collected by an electrode. Because these pulses are created very close together in the detector, they will arrive at the electrode at more or less the same time. This allows GERDA physicists to reject background events involving stray gamma rays scattering twice from different places in a detector. To be extra sure of rejecting such background events, GERDA also looks for flashes of light in the liquid argon, which are produced when gamma rays pass through. The experiment is also surrounded by a tank of water that eliminates background signals from cosmic rays. Now, after running with this configuration since December 2015, the team has announced that the measurement is essentially free of background signals. While the researchers have not seen any evidence for neutrinoless double-beta decay, they can say that the half-life for the process in germanium-76 is greater than about 5 ×1025 years. Because of the background-free nature of GERDA, expanding its size and running it for longer times could help physicists decide whether neutrinos are Majorana particles. The results are described in Nature.

 

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