Violent flaring revealed at the heart of a black hole system

It has the mass of about 7 Suns, with this collapsed down to a region of space smaller than the City of London.

OCTOBER 11, 2019

by University of Southampton

An international team of astronomers, led by the University of Southampton, have used state-of-the-art cameras to create a high frame-rate movie of a growing black hole system at a level of detail never seen before. In the process they uncovered new clues to understanding the immediate surroundings of these enigmatic objects. The scientists publish their work in a new paper in Monthly Notices of the Royal Astronomical Society.

Black holes can feed off a nearby star and create vast accretion discs of material. Here, the effect of the black hole’s strong gravity and the material’s own magnetic field can cause rapidly changing levels of radiation to be emitted from the system as a whole.

This radiation was detected in visible light by the HiPERCAM instrument on the Gran Telescopio Canarias (La Palma, Canary Islands) and in X-rays by NASA’s NICER observatory aboard the International Space Station.

The black hole system studied is named MAXI J1820+070, and was first discovered in early 2018. It is only about 10,000 lightyears away, in our own Milky Way. It has the mass of about 7 Suns, with this collapsed down to a region of space smaller than the City of London.

Investigating these systems is usually very difficult, as their distances make them too faint and too small to see – not even using the Event Horizon Telescope, which recently took a picture of the black hole at the centre of the galaxy M87. The HiPERCAM and NICER instruments however let the researchers record ‘movies’ of the changing light from the system at over three hundred frames per second, capturing violent ‘crackling’ and ‘flaring’ of visible and X-ray light.

Credit: University of Southampton

John Paice, a graduate student at the University of Southampton and the Inter-University Centre for Astronomy & Astrophysics in India was the lead author of the study presenting these results, and also the artist who created the movie. He explained the work as follows: “The movie was made using real data, but slowed down to 1/10th of actual speed to allow the most rapid flares to be discerned by the human eye. We can see how the material around the black hole is so bright, it’s outshining the star that it is consuming, and the fastest flickers last only a few milliseconds – that’s the output of a hundred Suns and more being emitted in the blink of an eye.”

Researchers also found that dips in X-ray levels are accompanied by a rise in visible light (and vice-versa). And the fastest flashes in visible light were found to emerge a fraction of a second after X-rays. Such patterns indirectly reveal the presence of distinct plasma, extremely hot material where electrons are stripped away from atoms, in structures deep in the embrace of the black hole’s gravity, otherwise too small to resolve.

This is not the first time this has been found; a split-second difference between X-ray and visual light has been seen in two other systems hosting black holes but it has never been observed at this level of detail. Members of this international team have been at the forefront of this field over the past decade. Dr Poshak Gandhi, also of Southampton, found the same fleeting time signatures in the two previous systems as well.

He commented on the significance of these findings: “The fact that we now see this in three systems strengthens the idea that it is a unifying characteristic of such growing black holes. If true, this must be telling us something fundamental about how plasma flows around black holes operate.

“Our best ideas invoke a deep connection between inspiralling and outflowing bits of the plasma. But these are extreme physical conditions that we cannot replicate in Earth laboratories, and we don’t understand how nature manages this. Such data will be crucial for homing in on the correct theory.”

Unlocking a 140-year-old secret in physics

In a new study in the journal Nature, an IBM Research-led collaboration describes an exciting breakthrough in a 140-year-old mystery in physics.

Image result for Unlocking a 140-year-old secret in physics images

OCTOBER 11, 2019

by IBM

Semiconductors are the basic building blocks of today’s digital, electronic age, providing us a multitude of devices that benefit our modern life, including computer, smartphones and other mobile devices. Improvements in semiconductor functionality and performance are likewise enabling next-generation applications of semiconductors for computing, sensing and energy conversion. Yet researchers have long struggled with limitations in our ability to fully understand the electronic charges inside semiconductor devices and advanced semiconductor materials, limiting our ability to drive further advances.

In a new study in the journal Nature, an IBM Research-led collaboration describes an exciting breakthrough in a 140-year-old mystery in physics—one that enables us to unlock the physical characteristics of semiconductors in much greater detail and aid in the development of new and improved semiconductor materials.

To truly understand the physics of semiconductors, we first need to know the fundamental properties of the charge carriers inside the materials, whether those particles are positive or negative, their speed under an applied electric field and how densely they are packed in the material. Physicist Edwin Hall found a way to determine those properties in 1879, when he discovered that a magnetic field will deflect the movement of electronic charges inside a conductor and that the amount of deflection can be measured as a voltage perpendicular to the flow of charge as shown in Fig. 1a. This voltage, known as the Hall voltage, unlocks essential information about the charge carriers in a semiconductor, including whether they are negative electrons or positive quasi-particles called “holes,” how fast they move in an electric field or their “mobility” (µ) and their density (n) inside the semiconductor.

A 140-year-old secret

Decades after Hall’s discovery, researchers also recognized that they can perform the Hall effect measurement with light—which are called photo-Hall experiments, as shown in Fig. 1b. In such experiments, the light illumination generates multiple carriers or electron–holes pairs in the semiconductors. Unfortunately, our understanding of the basic Hall effect provided insights into only the dominant charge carrier (or majority carrier). The researchers were unable to extract the properties of both carriers (the majority and minority carriers) simultaneously. Such information is crucial for many applications that involve light such as solar cells and other optoelectronic devices.

IBM Research’s study in Nature unlocks one of the Hall effect’s long-held secret. Researchers from KAIST (Korea Advanced Institute of Science and Technology), KRICT (Korea Research Institute of Chemical Technology), Duke University, and IBM discovered a new formula and technique that enable us to simultaneously extract the majority and minority carrier information such as their density and mobility, as well as gain additional insights about carrier lifetimes, diffusion lengths and the recombination process.

To be more specific, in the photo-Hall experiment, both carriers contribute to changes in conductivity (σ) and Hall coefficient (H, which is proportional to the ratio of the Hall voltage to the magnetic field). The key insight comes from measuring the conductivity and Hall coefficient as a function of light intensity. Hidden in the trajectory of the conductivity- Hall coefficient (σ-H) curve, reveals a crucial new information: the difference in mobility of both carriers. As discussed in the paper, this relationship can be expressed elegantly as: Δµ = d (σ²H)/dσ

**Unlocking a 140-year-old secret in physics

Starting with a known majority carrier density from the traditional Hall measurement in the dark, we can solve for both majority and minority carrier mobility and density as a function of light intensity. The team named the new technique Carrier-Resolved Photo Hall (CRPH) measurement. With a known light illumination intensity, the carrier lifetime can similarly be established. This relationship and the related solutions have been hidden for nearly a century and a half, since the discovery of the Hall effect.

Beyond advances in this theoretical understanding, advances in experimental techniques are also critical to enabling this new technique. The technique requires a clean Hall signal measurement, which can be challenging for materials where the Hall signal is weak (e.g. due to low mobility) or when extra unwanted signals are present, such as under strong light illumination. For this purpose, one needs to perform the Hall measurement with an oscillating (ac) magnetic field. Like listening to radio, one must select the desired station’s frequency while rejecting all other frequencies that act as noise. The CRPH technique goes a step further and selects not only the desired frequency, but also to the phase of the oscillating magnetic field in a technique called lock-in detection. This concept of ac Hall measurement has long been known, but the traditional technique using an electromagnetic coil system to generate the ac magnetic field was inefficient.

A precursor discovery

As often occurs in science, advances in one area are triggered by discoveries in another. In 2015, IBM Research reported a previously unknown phenomenon in physics related to a new magnetic field confinement effect, nicknamed the “camelback” effect, which occurs between two lines of transverse dipoles when they exceed a critical length as shown in Fig. 2a. The effect is a key feature that enables a new type of natural magnetic trap, called parallel dipole line (PDL) trap as shown in Fig. 2b. The PDL magnetic trap could serve as novel platform for various sensor applications such as a tiltmeter and seismometer (earthquake sensor). Such novel sensor systems together with big data technology could open many new applications and are being studied by the IBM Research team developing a big data analytics platform called IBM Physical Analytics Integrated Repository Service (PAIRS), which hosts myriad geospatial and Internet of Things (IoT) sensor data.

Surprisingly, the same PDL element has another unique application. When rotated, it serves as an ideal system for a photo-Hall experiment to obtain strong, unidirectional and pure harmonic magnetic field oscillation (Fig 2c). More importantly, the system provides ample space to allow large area illumination onto the sample, which is critical in the photo-Hall experiment.

The impact

The newly developed photo-Hall technique allows us to extract an astonishing amount of information from semiconductors. In contrast to only three parameters obtained in the classical Hall measurement, this new technique yields up to seven parameters at every tested light intensity. These include the mobility for both electron and hole; their carrier density under light; recombination lifetime; and diffusion lengths for electron, holes and ambipolar type. All of these can be repeated N times (i.e. the number of light intensity settings used in the experiment).

This new discovery and technology will help push semiconductor advances in both existing and emerging technologies. We now have the knowledge and tools needed to extract the physical characteristics of semiconductor materials in great detail. For example, this will help accelerate development of next generation semiconductor technology such as better solar cells, better optoelectronics devices and new materials and devices for artificial intelligence technology.

Honeybees can count and do math

Image result for Honeybees are math stars images

OCTOBER 10, 2019

Honeybees were very cooperative, especially when I was providing sugar rewards!

by The Company of Biologists

Start thinking about numbers and they can become large very quickly. The diameter of the universe is about 8.8×1023 km and the largest known number—googolplex, 1010100—outranks it enormously. Although that colossal concept was dreamt up by brilliant mathematicians, we’re still pretty limited when it comes to assessing quantities at a glance. ‘Humans have a threshold limit for instantly processing one to four elements accurately’, says Adrian Dyer from RMIT University, Australia; and it seems that we are not alone. Scarlett Howard from RMIT and the Université de Toulouse, France, explains that guppies, angelfish and even honeybees are capable of distinguishing between quantities of three and four, although the trusty insects come unstuck at finer differences; they fail to differentiate between four and five, which made her wonder. According to Howard, honeybees are quite accomplished mathematicians. ‘Recently, honeybees were shown to learn the rules of “less than” and “greater than” and apply these rules to evaluate numbers from zero to six’, she says. Maybe numeracy wasn’t the bees’ problem; was it how the question was posed? The duo publishes their discovery that bees can discriminate between four and five if the training procedure is correct in Journal of Experimental Biology.

Honeybees are math stars
A ‘bee eye’ view of the 4 and 5 element cards that were used to test bee number discrimination. The insert shows how humans see the same cards. Credit: Adrian Dyer

Dyer explains that when animals are trained to distinguish between colours and objects, some training procedures simply reward the animals when they make the correct decision. In the case of the honeybees that could distinguish three from four, they received a sip of super-sweet sugar water when they made the correct selection but just a taste of plain water when they got it wrong. However, Dyer, Howard and colleagues Aurore Avarguès-Weber, Jair Garcia and Andrew Greentree knew there was an alternative strategy. This time, the bees would be given a bitter-tasting sip of quinine-flavoured water when they got the answer wrong. Would the unpleasant flavour help the honeybees to focus better and improve their maths?

‘[The] honeybees were very cooperative, especially when I was providing sugar rewards’, says Howard, who moved to France each April to take advantage the northern summer during the Australian winter, when bees are dormant. Training the bees to enter a Y-shaped maze, Howard presented the insects with a choice; a card featuring four shapes in one arm and a card featuring a different number of shapes (ranging from one to 10) in the other. During the first series of training sessions, Howard rewarded the bees with a sugary sip when they alighted correctly before the card with four shapes, in contrast to a sip of water when they selected the wrong card. However, when Howard trained a second set of bees she reproved them with a bitter-tasting sip of quinine when they chose incorrectly, rewarding the insects with sugar when they selected the card with four shapes. Once the bees had learned to pick out the card with four shapes, Howard tested whether they could distinguish the card with four shapes when offered a choice between it and cards with eight, seven, six or—the most challenging comparison—five shapes.

Not surprisingly, the bees that had only been rewarded during training struggled; they couldn’t even differentiate between four and eight shapes. However, when Howard tested the honeybees that had been trained more rigorously—receiving a quinine reprimand—their performance was considerably better, consistently picking the card with four shapes when offered a choice between it and cards with seven or eight shapes. Even more impressively, the bees succeeded when offered the more subtle choice between four and five shapes.

So, it seems that honeybees are better mathematicians than had been credited. Unlocking their ability was simply a matter of asking the question in the right way and Howard is now keen to find out just how far counting bees can go.

MIT alumna addresses the world’s mounting plastic waste problem

Renewlogy co-founder and CEO Priyanka Bakaya inside one of the company's commercial plants, which are capable of processing ten tons of plastic each day to create about 60 barrels of fuel.
Renewlogy co-founder and CEO Priyanka Bakaya inside one of the company’s commercial plants, which are capable of processing ten tons of plastic each day to create about 60 barrels of fuel.
Image courtesy of Renewlogy

Renewlogy’s system is converting plastic waste from cities and rivers into fuel.

Zach Winn | MIT News Office
October 9, 2019

It’s been nearly 10 years since Priyanka Bakaya MBA ’11 founded Renewlogy to develop a system that converts plastic waste into fuel. Today, that system is being used to profitably turn even nonrecyclable plastic into high-value fuels like diesel, as well as the precursors to new plastics.

Since its inception, Bakaya has guided Renewlogy through multiple business and product transformations to maximize its impact. During the company’s evolution from a garage-based startup to a global driver of sustainability, it has licensed its technology to waste management companies in the U.S. and Canada, created community-driven supply chains for processing nonrecycled plastic, and started a nonprofit, Renew Oceans, to reduce the flow of plastic into the world’s oceans.

The latter project has brought Bakaya and her team to one of the most polluted rivers in the world, the Ganges. With an effort based in Varanasi, a city of much religious, political, and cultural significance in India, Renew Oceans hopes to transform the river basin by incentivizing residents to dispose of omnipresent plastic waste in its “reverse vending machines,” which provide coupons in exchange for certain plastics.

Each of Renewlogy’s initiatives has brought challenges Bakaya never could have imagined during her early days tinkering with the system. But she’s approached those hurdles with a creative determination, driven by her belief in the transformative power of the company.

“It’s important to focus on big problems you’re really passionate about,” Bakaya says. “The only reason we’ve stuck with it over the years is because it’s extremely meaningful, and I couldn’t imagine working this hard and long on something if it wasn’t deeply meaningful.”

A system for sustainability

Bakaya began working on a plastic-conversion system with Renewlogy co-founder and Chief Technology Officer Benjamin Coates after coming to MIT’s Sloan School of Management in 2009. While pursuing his PhD at the University of Utah, Coates had been developing continuously operating systems to create fuels from things like wood waste and algae conversion.

One of Renewlogy’s key innovations is using a continuous system on plastics, which saves energy by eliminating the need to reheat the system to the high temperatures necessary for conversion.

Today, plastics entering Renewlogy’s system are first shredded, then put through a chemical reformer, where a catalyst degrades their long carbon chains.

Roughly 15 to 20 percent of those chains are converted into hydrocarbon gas that Renewlogy recycles to heat the system. Five percent turns into char, and the remaining 75 percent is converted into high-value fuels. Bakaya says the system can create about 60 barrels of fuel for every 10 tons of plastic it processes, and it has a 75 percent lower carbon footprint when compared to traditional methods for extracting and distilling diesel fuel.

In 2014, the company began running a large-scale plant in Salt Lake City, where it continues to iterate its processes and hold demonstrations.

Since then, Renewlogy has set up another commercial-scale facility in Nova Scotia, Canada, where the waste management company Sustane uses it to process about 10 tons of plastic a day, representing 5 percent of the total amount of solid waste the company collects. Renewlogy is also building a similar-sized facility in Phoenix, Arizona, that will be breaking ground next year. That project focuses on processing specific types of plastics (identified by international resin codes 3 through 7) that are less easily recycled.

In addition to its licensing strategy, the company is spearheading grassroots efforts to gather and process plastic that’s not normally collected for recycling, as part of the Hefty Energy Bag Program.

Through the program, residents in cities including Boise, Idaho, Omaha, Nebraska, and Lincoln, Nebraska, can put plastics numbered 4 through 6 into their regular recycling bins using special orange bags. The bags are separated at the recycling facility and sent to Renewlogy’s Salt Lake City plant for processing.

The projects have positioned Renewlogy to continue scaling and have earned Bakaya entrepreneurial honors from the likes of ForbesFortune, and the World Economic Forum. But a growing crisis in the world’s oceans has drawn her halfway across the world, to the site of the company’s most ambitious project yet.

Renewing the planet’s oceans

Of the millions of tons of plastic waste flowing through rivers into the world’s oceans each year, roughly 90 percent comes from just 10 rivers. The worsening environmental conditions of these rivers represents a growing global crisis that state governments have put billions of dollars toward, often with discouraging results.

Bakaya believes she can help.

“Most of these plastics tend to be what are referred to as soft plastics, which are typically much more challenging to recycle, but are a good feedstock for Renewlogy’s process,” she says.

Bakaya started Renew Oceans as a separate, nonprofit arm of Renewlogy last year. Since then, Renew Oceans has designed fence-like structures to collect river waste that can then be brought to its scaled down machines for processing. These machines can process between 0.1 and 1 ton of plastic a day.

Renew Oceans has already built its first machine, and Bakaya says deciding where to put it was easy.

From its origins in the Himalayas, the Ganges River flows over 1,500 miles through India and Bangladesh, serving as a means of transportation, irrigation, energy, and as a sacred monument to millions of people who refer to it as Mother Ganges.

Renewlogy’s first machine is currently undergoing local commissioning in the Indian city of Varanasi. Bakaya says the project is designed to scale.

“The aim is to take this to other major polluted rivers where we can have maximum impact,” Bakaya says. “We’ve started with the Ganges, but we want to go to other regions, especially around Asia, and find circular economies that can support this in the long term so locals can derive value from these plastics.”

Scaling down their system was another unforeseen project for Bakaya and Coates, who remember scaling up prototypes during the early days of the company. Throughout the years, Renewlogy has also adjusted its chemical processes in response to changing markets, having begun by producing crude oil, then moving to diesel as oil prices plummeted, and now exploring ways to create high-value petrochemicals like naphtha, which can be used to make new plastics.

Indeed, the company’s approach has featured almost as many twists and turns as the Ganges itself. Bakaya says she wouldn’t have it any other way.

“I’d really encourage entrepreneurs to not just go down that easy road but to really challenge themselves and try to solve big problems — especially students from MIT. The world is kind of depending on MIT students to push us forward and challenge the realm of possibility. We all should feel that sense of responsibility to solve bigger problems.”

For newborn planets, solar systems are naturally baby-proof

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OCTOBER 10, 2019

by Max Planck Society

Numerical simulations by a group of astronomers, led by Mario Flock from the Max Planck Institute for Astronomy, have shown that young planetary systems are naturally “baby-proof”: Physical mechanisms combine to keep young planets in the inner regions from taking a fatal plunge into the star. Similar processes also allow planets to be born close to stars—from pebbles trapped in a region close to the star. The research, which has been published in the journal Astronomy & Astrophysics, explains findings by the Kepler space telescopes that show a large number of super-Earths orbiting their stars very closely, at the edge of the baby-proof region.

When a child is born, parents will make sure they have baby-proofed their home, setting up safety barriers which keep the child away from particularly dangerous areas. New research on the formation of planets show that something very similar happens in young planetary systems.

Planets form around a young star, which is surrounded by a disk of gas and dust. Inside this protoplanetary disk, dust grains stick together, growing larger and larger. After a few million years, they have reached a few kilometers in diameter. At that point, gravity is strong enough to pull such objects together to form planets, round objects, solid or with a solid core, with diameters of a few thousand kilometers or more.

A curious crowding at the inner boundary

Just like toddlers, solid objects in such a young planetary system tend to move in all directions—not only orbiting around the star, but drifting inwards or outwards. This can become potentially fatal for planets that are already relatively close to the central star.

Near the star, we will only encounter rocky planets, with solid surfaces, similar to our Earth. Planetary cores can only capture and keep significant amounts of gas to become gas giants much further out, away from the hot star. But the simplest kind of calculation for the motion of a planet near the star, in the gas of a protoplanetary disk, shows that such a planet should continually drift inwards, plunging into the star on a time scale of less than a million year, much shorter than the lifetime of the disk.

If this were the whole picture, it would be puzzling that NASA’s Kepler satellite, examining stars similar to the sun (spectral types F, G and K), found something completely different: numerous stars have very closely orbiting so-called super-Earths, rocky planets that are more massive than our own Earth. Particularly common are planets with periods around 12 days, going down to periods as low as 10 days. For our sun, that would correspond to orbital radii around 0.1 astronomical units, only about one quarter of the orbital radius of Mercury, the planet closest to our sun in our own solar system.

This was the puzzle that Mario Flock, a group leader at the Max Planck Institute for Astronomy, set out to solve, together with colleagues from the Jet Propulsion Laboratory, the University of Chicago and Queen Mary University, London. The researchers involved are experts in simulating the complex environment in which planets are born, modelling the flows and interactions of gas, dust, magnetic fields, and of planets and their various precursor stages. Faced with the apparent paradox of the close-orbit Kepler super-Earths, they set out to simulate planet formation close to sun-like stars in detail.

Solar-system-scale baby-proofing

Their results were unequivocal, and suggest two possible reasons behind the common occurrence of closely-orbiting planets. The first is that, at least for rocky planets with masses of up to 10 times the mass of the Earth (“super-Earths” or “Mini-Neptunes”), those early star systems are baby-proof.

The safety barrier keeping young planets out of the danger zone works as follows. The closer we get to the star, the more intense the star’s radiation. Inside boundary called the silicate sublimation front, the disk temperature rises above 1200 K, and dust particles (silicates) will turn to gas. The extremely hot gas inside that region becomes very turbulent. This turbulence transports the gas towards the star at high speed, thinning out the inner region of the disk in the process.

As a young super-Earth travels through the gas, it is typically accompanied by gas co-rotating with the planet on an orbital path similar to an horseshoe. As the planet drifts inward and reaches the silicate sublimation front, the gas particles moving from the hot thinner gas to the denser gas outside the boundary give the planet a small kick. In this situation, the gas will exert an influence (in physics terms: a torque) on the travelling planet, and crucially, due to the jump in density, that influence will draw the planet away from the boundary, radially outward. In this way, the boundary serves as a safety barrier, keeping the young planets from plunging into the star. And the location of the boundary for a sun-like star, as predicted by the simulation, corresponds to the lower limit for orbital periods found by Kepler. As Mario Flock says: “Why are there so many super-Earths in close orbit, as Kepler has shown us? Because young planetary systems have a built-in baby-proof barrier.”

Planet-building at the boundary

There is an alternative possibility: In tracing the movement of pebble-like, smaller objects a few millimeters or centimeters in size, the researchers found that such pebbles tend to collect closely behind the silicate sublimation front. In order for pressure to balance directly at the border, the thin gas in the transition region needs to rotate faster than usual (since there must be a balance between pressure and centrifugal force). This gas rotation is faster than the “Keplerian” orbital speed of an isolated particle orbiting the star on its own. A pebble that enters this transition region is forced into this faster-than-Keplerian motion, and immediately ejected again as the corresponding centrifugal forces push it outwards, like a small child sliding off the platform of a merry-go-round. This, too contributes to the frequency of closely orbiting super-Earths. Not only do previously formed super-Earths collect at a baby-proof barrier. The fact that pebbles collect at that barrier as well provides ideal conditions for super-Earth newly forming at that location.

The results did not come as a complete surprise for the researchers. In fact, they had found a similar pebble trap in models of much heavier stars (“Herbig stars”), although at a much greater distance from the star. The new results extend this to sun-like stars, and they add the baby-proofing mechanism for newborn planets. Furthermore, the new article is the first that provides a comparison with statistical data from the Kepler space telescope, carefully taking into account that Kepler will only be able to see certain kinds of systems (notably where we see the orbital plane nearly edge-on).

What about our own solar system?

Interestingly, by these criteria, our own solar system could also have harbored an earth-like planet closer to the sun than the current innermost planet, Mercury. Is the fact that there is no such planet a statistical fluke, or did such a planet exist and was ejected from the solar system at some time? That is one interesting question for additional research. As Mario Flock says: “Not only that our solar system was baby-proof—it is possible that the baby thus protected has since ‘flown the nest’.”

Physics researchers break new ground, explore unknown energy regions

Physics researchers break new ground, explore unknown energy regions
Florida State graduate student Jason Barlow works on a part of the GlueX detector at Jefferson National Laboratory. FSU scientists painted their part of the GlueX detector they built garnet and gold. Credit: Florida State University

OCTOBER 10, 2019

by Kathleen Haughney, Florida State University

Florida State University physicists are using photon-proton collisions to capture particles in an unexplored energy region, yielding new insights into the matter that binds parts of the nucleus together.

“We want to understand not just the nucleus, but everything that makes up the nucleus,” said FSU Professor of Physics Paul Eugenio. “We’re working to understand the particles and forces that make up our world.”

FSU’s hadronic physics group is a leading member of the GlueX Collaboration at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility. The group ran highly sophisticated experiments around the clock for months at a time over several years starting in 2016. Their main goal is to ferret out new information about the material—called the gluonic field—that ties together quarks. Quarks are fundamental particles that create protons and neutrons.

In a new paper published in Physical Review Letters , the hadronic physics group at Florida State University and their collaborators laid out the first-ever measurements of a subatomic particle—called the J/psi particle— created out of the energy in the photon-proton collisions.

“It’s really cool to see,” said Assistant Professor of Physics Sean Dobbs. “This is opening up a new frontier of physics.”

When researchers run these experiments, they blast a photon beam into the GlueX spectrometer where it passes through a canister of liquid hydrogen and reacts with the protons in the nucleus of these hydrogen atoms. From there, the detectors measure the particles created in these collisions, which allows physicists to reconstruct the details of the collision and learn more about the created particles.

Dobbs compared it to a car wreck. You might not see the wreck happen, but you see the result and can work backward. In this case, researchers collected about one to two million gigabytes of data per year through this process to try to piece together the puzzle.

The J/psi particle is composed of a pair of quarks—a charm quark and an anti-charm quark. In measuring the J/psi particle in these collisions, scientists can also look for the production of other charm quark-containing subatomic particles.

The measurements were taken at an energy threshold below where previous studies looked at production levels, meaning it was more sensitive to the distribution of the gluons in the proton and their contributions to the proton mass.

Scientists found a much larger production of J/psi particles than expected, meaning this gluonic structure is a big contributor to the mass of the proton structure, and thus the nucleus as a whole. These initial measurements suggest that the gluons directly contribute more than 80 percent of the mass of the proton. Further measurements of these reactions currently underway will give more insight into how the gluons are distributed around the nucleon.

These measurements also brought into question observations from experiments on the Large Hadron Collider, a particle detector at CERN, the European Organization for Nuclear Research. Scientists there briefly glimpsed what they are calling pentaquarks—short lived particles made of five quarks.

FSU physicists did not specifically see pentaquarks in their data, which has ruled out several models which attempt to describe the structure of these pentaquarks. Further measurements underway are expected to give a more definitive answer on how the five quarks are arranged in these particles.

New method visualizes groups of neurons as they compute

Fluorescent probe could allow scientists to watch circuits within the brain and link their activity to specific behaviors.

In the top row, neurons are labeled with a fluorescent probe that reveals electrical activity. In the bottom row, neurons are labeled with a variant of the probe that accumulates specifically in the neuron cell bodies, preventing interference from axons of neighboring neurons.
In the top row, neurons are labeled with a fluorescent probe that reveals electrical activity. In the bottom row, neurons are labeled with a variant of the probe that accumulates specifically in the neuron cell bodies, preventing interference from axons of neighboring neurons.
Image courtesy of the researchers

Anne Trafton | MIT News Office
October 9, 2019

Using a fluorescent probe that lights up when brain cells are electrically active, MIT and Boston University researchers have shown that they can image the activity of many neurons at once, in the brains of mice.

This technique, which can be performed using a simple light microscope, could allow neuroscientists to visualize the activity of circuits within the brain and link them to specific behaviors, says Edward Boyden, the Y. Eva Tan Professor in Neurotechnology and a professor of biological engineering and of brain and cognitive sciences at MIT.

“If you want to study a behavior, or a disease, you need to image the activity of populations of neurons because they work together in a network,” says Boyden, who is also a member of MIT’s McGovern Institute for Brain Research, Media Lab, and Koch Institute for Integrative Cancer Research.

Using this voltage-sensing molecule, the researchers showed that they could record electrical activity from many more neurons than has been possible with any existing, fully genetically encoded, fluorescent voltage probe.

Boyden and Xue Han, an associate professor of biomedical engineering at Boston University, are the senior authors of the study, which appears in the Oct. 9 online edition of Nature. The lead authors of the paper are MIT postdoc Kiryl Piatkevich, BU graduate student Seth Bensussen, and BU research scientist Hua-an Tseng.

Seeing connections

Neurons compute using rapid electrical impulses, which underlie our thoughts, behavior, and perception of the world. Traditional methods for measuring this electrical activity require inserting an electrode into the brain, a process that is labor-intensive and usually allows researchers to record from only one neuron at a time. Multielectrode arrays allow the monitoring of electrical activity from many neurons at once, but they don’t sample densely enough to get all the neurons within a given volume.  Calcium imaging does allow such dense sampling, but it measures calcium, an indirect and slow measure of neural electrical activity.

In 2018, Boyden’s team developed an alternative way to monitor electrical activity by labeling neurons with a fluorescent probe. Using a technique known as directed protein evolution, his group engineered a molecule called Archon1 that can be genetically inserted into neurons, where it becomes embedded in the cell membrane. When a neuron’s electrical activity increases, the molecule becomes brighter, and this fluorescence can be seen with a standard light microscope.

In the 2018 paper, Boyden and his colleagues showed that they could use the molecule to image electrical activity in the brains of transparent worms and zebrafish embryos, and also in mouse brain slices. In the new study, they wanted to try to use it in living, awake mice as they engaged in a specific behavior.

To do that, the researchers had to modify the probe so that it would go to a subregion of the neuron membrane. They found that when the molecule inserts itself throughout the entire cell membrane, the resulting images are blurry because the axons and dendrites that extend from neurons also fluoresce. To overcome that, the researchers attached a small peptide that guides the probe specifically to membranes of the cell bodies of neurons. They called this modified protein SomArchon.

“With SomArchon, you can see each cell as a distinct sphere,” Boyden says. “Rather than having one cell’s light blurring all its neighbors, each cell can speak by itself loudly and clearly, uncontaminated by its neighbors.”

The researchers used this probe to image activity in a part of the brain called the striatum, which is involved in planning movement, as mice ran on a ball. They were able to monitor activity in several neurons simultaneously and correlate each one’s activity with the mice’s movement. Some neurons’ activity went up when the mice were running, some went down, and others showed no significant change.

“Over the years, my lab has tried many different versions of voltage sensors, and none of them have worked in living mammalian brains until this one,” Han says.

Using this fluorescent probe, the researchers were able to obtain measurements similar to those recorded by an electrical probe, which can pick up activity on a very rapid timescale. This makes the measurements more informative than existing techniques such as imaging calcium, which neuroscientists often use as a proxy for electrical activity.

“We want to record electrical activity on a millisecond timescale,” Han says. “The timescale and activity patterns that we get from calcium imaging are very different. We really don’t know exactly how these calcium changes are related to electrical dynamics.”

With the new voltage sensor, it is also possible to measure very small fluctuations in activity that occur even when a neuron is not firing a spike. This could help neuroscientists study how small fluctuations impact a neuron’s overall behavior, which has previously been very difficult in living brains, Han says.

The study “introduces a new and powerful genetic tool” for imaging voltage in the brains of awake mice, says Adam Cohen, a professor of chemistry, chemical biology, and physics at Harvard University.

“Previously, researchers had to impale neurons with fine glass capillaries to make electrical recordings, and it was only possible to record from one or two cells at a time. The Boyden team recorded from about 10 cells at a time. That’s a lot of cells,” says Cohen, who was not involved in the research. “These tools open new possibilities to study the statistical structure of neural activity. But a mouse brain contains about 75 million neurons, so we still have a long way to go.”

Mapping circuits

The researchers also showed that this imaging technique can be combined with optogenetics — a technique developed by the Boyden lab and collaborators that allows researchers to turn neurons on and off with light by engineering them to express light-sensitive proteins. In this case, the researchers activated certain neurons with light and then measured the resulting electrical activity in these neurons.

This imaging technology could also be combined with expansion microscopy, a technique that Boyden’s lab developed to expand brain tissue before imaging it, make it easier to see the anatomical connections between neurons in high resolution.

“One of my dream experiments is to image all the activity in a brain, and then use expansion microscopy to find the wiring between those neurons,” Boyden says. “Then can we predict how neural computations emerge from the wiring.”

Such wiring diagrams could allow researchers to pinpoint circuit abnormalities that underlie brain disorders, and may also help researchers to design artificial intelligence that more closely mimics the human brain, Boyden says.

The MIT portion of the research was funded by Edward and Kay Poitras, the National Institutes of Health, including a Director’s Pioneer Award, Charles Hieken, John Doerr, the National Science Foundation, the HHMI-Simons Faculty Scholars Program, the Human Frontier Science Program, and the U.S. Army Research Office.

Researchers theorize origins of magnetars, the strongest magnets in the universe

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OCTOBER 9, 2019

by Heidelberg University

How do some neutron stars become the strongest magnets in the universe?

A German-British team of astrophysicists has found a possible answer to the question of how magnetars form. They used large computer simulations to demonstrate how the merger of two stars creates strong magnetic fields. If such stars explode in supernovae, magnetars can result. Scientists from Heidelberg University, the Max Planck Society, the Heidelberg Institute for Theoretical Studies, and the University of Oxford were involved in the research. The results were published in Nature.

The universe is threaded by magnetic fields. The sun, for example, has an envelope in which convection continuously generates magnetic fields. “Even though massive stars have no such envelopes, we still observe a strong, large-scale magnetic field at the surface of about 10 percent of them,” explains Dr. Fabian Schneider from the Centre for Astronomy of Heidelberg University, who is the first author of the study in Nature. Although such fields were discovered in 1947, their origin has remained elusive so far.

Over a decade ago, scientists suggested that strong magnetic fields are produced when two stars collide. “But until now, we weren’t able to test this hypothesis because we didn’t have the necessary computational tools,” says Dr. Sebastian Ohlmann from the computing centre of the Max Planck Society in Garching near Munich. This time, the researchers used the AREPO code, a highly dynamic simulation code running on computer clusters of the Heidelberg Institute for Theoretical Studies (HITS), to explain the properties of Tau Scorpii (τ Sco), a magnetic star located 500 light years from Earth.

How do the strongest magnets in the universe form?
The simulation marks the birth of a magnetic star such as Tau Scorpii. The image is a cut through the orbital plane where the coloring indicates the strength of the magnetic field and the light hatching reflects the direction of the magnetic field line. Credit: Ohlmann/Schneider/Röpke

In 2016, Fabian Schneider and Philipp Podsiadlowski from the University of Oxford realised that τ Sco is a so-called blue straggler. Blue stragglers are the product of merged stars. “We assume that Tau Scorpii obtained its strong magnetic field during the merger process,” explains Prof. Dr. Philipp Podsiadlowski. Through its computer simulations of τ Sco, the German-British research team has now demonstrated that strong turbulence during the merger of two stars can create such a field.

Stellar mergers are relatively frequent. Scientists assume that about 10 percent of all massive stars in the Milky Way are the products of such processes. This is in good agreement with the occurrence rate of magnetic massive stars, according to Dr. Schneider. Astronomers think that these very stars could form magnetars when they explode in supernovae.

This may also happen to τ Sco when it explodes at the end of its life. The computer simulations suggest that the magnetic field generated would be sufficient to explain the exceptionally strong magnetic fields in magnetars. “Magnetars are thought to have the strongest magnetic fields in the universe—up to 100 million times stronger than the strongest magnetic field ever produced by humans,” says Friedrich Röpke from HITS.

Physicists report a way to ‘hear’ dark matter

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OCTOBER 9, 2019

by Stockholm University

Physicists at Stockholm University and the Max Planck Institute for Physics have turned to plasmas in a proposal that could revolutionise the search for the elusive dark matter.

Dark matter makes up 85 percent of the matter in the universe. Originally introduced to explain why the strong force, which holds together protons and neutrons, is the same backwards and forwards in time, the so-called axion would provide a natural explanation for dark matter. Rather than discrete particles, axion dark matter would form a pervasive wave flowing throughout space.

The axion is one of the best explanations for dark matter, but has only recently been the focus of large-scale experimental effort. Now, there is a rush to come up with new ideas to find the axion in all the areas where it could be hiding.

“Finding the axion is a bit like tuning a radio: You have to tune your antenna until you pick up the right frequency. Rather than music, experimentalists would be rewarded with ‘hearing’ the dark matter that the Earth is traveling through. Despite being well motivated, axions have been experimentally neglected during the three decades since they were named by coauthor Frank Wilczek,” says Dr. Alexander Millar at the Department of Physics, Stockholm University, and author of the study.

The key insight of the research team’s new study is that inside a magnetic field, axions would generate a small electric field that could be used to drive oscillations in the plasma. In a plasma, charged particles such as electrons can flow freely as a fluid. These oscillations amplify the signal, leading to a better “axion radio.” Unlike traditional experiments based on resonant cavities, there is almost no limit on how large these plasmas can be, thus providing a larger signal. The difference is somewhat like the difference between a walkie talkie and a radio broadcast tower.

“Without the cold plasma, axions cannot efficiently convert into light. The plasma plays a dual role, both creating an environment which allows for efficient conversion, and providing a resonant plasmon to collect the energy of the converted dark matter,” says Dr. Matthew Lawson, Postdoctor at the Department of Physics, Stockholm University, also author of the study.

“This is totally a new way to look for dark matter, and will help us search for one of the strongest dark matter candidates in areas that are just completely unexplored. Building a tuneable plasma would allow us to make much larger experiments than traditional techniques, giving much stronger signals at high frequencies,” says Dr. Alexander Millar.

To tune this “axion radio,” the authors propose using something called a “wire metamaterial,” a system of wires thinner than hair that can be moved to change the characteristic frequency of the plasma. Inside a large, powerful magnet, similar to those used in magnetic resonance imaging machines in hospitals, a wire metamaterial turns into a very sensitive axion radio.

In close collaboration with the researchers, an experimental group at Berkeley has been doing research and development on the concept with the intent of building such an experiment in the near future.

“Plasma haloscopes are one of the few ideas to search for axions in this parameter space. The fact that the experimental community has latched onto this idea so quickly is very exciting and promising for building a full scale experiment,” says Dr. Alexander Millar.

Physicists measure the variation of the top-quark mass for the first time

Physicists measure the variation of the top-quark mass for the first time

OCTOBER 8, 2019

by Ana Lopes, CERN

For the first time, CMS physicists have investigated an effect called the “running” of the top quark mass, a fundamental quantum effect predicted by the Standard Model.

Mass is one of the most complex concepts in fundamental physics, which went through a long history of conceptual developments. Mass was first understood in classical mechanics as a measure of inertia and was later interpreted in the theory of special relativity as a form of energy.  Mass has a similar meaning in modern quantum field theories that describe the subatomic world. The Standard Model of particle physics is such a quantum field theory, and it can describe the interaction of all known fundamental particles at the energies of the Large Hadron Collider.

Quantum Chromodynamics is the part of the Standard Model that describes the interactions of fundamental constituents of nuclear matter: quarks and gluons. The strength of the interaction between these particles depends on a fundamental parameter called the strong coupling constant. According to Quantum Chromodynamics, the strong coupling constant rapidly decreases at higher energy scales. This effect is called asymptotic freedom, and the scale evolution is referred to as the “running of the coupling constant.” The same is also true for the masses of the quarks, which can themselves be understood as fundamental couplings, for example, in connection with the interaction with the Higgs field. In Quantum Chromodynamics, the running of the strong coupling constant and of the quark masses can be predicted, and these predictions can be experimentally tested.

Physicists measure the variation of the top-quark mass for the first time
Display of an LHC collision detected by the CMS detector that contains a reconstructed top quark-antiquark pair. The display shows an electron (green) and a muon (red) of opposite charge, two highly energetic jets (orange) and a large amount of missing energy (purple). Credit: CERN

The experimental verification of the running mass is an essential test of the validity of Quantum Chromodynamics. At the energies probed by the Large Hadron Collider, the effects of physics beyond the Standard Model could lead to modifications of the running of mass. Therefore, a measurement of this effect is also a search for unknown physics. Over the past decades, the running of the strong coupling constant has been experimentally verified for a wide range of scales. Also, evidence was found for the running of the masses of the charm and beauty quarks.

With a new measurement, the CMS Collaboration investigates for the first time the running of the mass of the heaviest of the quarks: the top quark. The production rate of top quark pairs (a quantity that depends on the top quark mass) was measured at different energy scales. From this measurement, the top quark mass is extracted at those energy scales using theory predictions that predict the rate at which top quark-antiquark pairs are produced.

Physicists measure the variation of the top-quark mass for the first time
The running of the top quark mass determined from the data (black points) compared to the theoretical prediction (red line). As the absolute scale of the top quark mass is not relevant for this measurement, the values have been normalised to the second data point. Credit: CERN

Experimentally, interesting top quark pair collisions are selected by searching for the specific decay products of a top quark-antiquark pair. In the overwhelming majority of cases, top quarks decay into an energetic jet and a W boson, which in turn can decay into a lepton and a neutrino. Jets and leptons can be identified and measured with high precision by the CMS detector, while neutrinos escape undetected and reveal themselves as missing energy. A collision that is likely the production of a top quark-antiquark pair as it is seen in the CMS detector is shown in Figure 1. Such a collision is expected to contain an electron, a muon, two energetic jets, and a large amount of missing energy.

The measured running of the top quark mass is shown in Figure 2. The markers correspond to the measured points, while the red line represents the theoretical prediction according to  Quantum Chromodynamics. The result provides the first indication of the validity of the fundamental quantum effect of the running of the top quark mass and opens a new window to test our understanding of the strong interaction. While a lot more data will be collected in the future LHC runs starting with Run 3 in 2021, this particular CMS result is mostly sensitive to uncertainties coming from the theoretical knowledge of the top quark in Quantum Chromodynamics. To witness the top quark mass running with even higher precision and maybe unveil signs of new physics, theory developments and experimental efforts will both be necessary. In the meantime, watch the top quark run!