Magnetic-field

In a very high magnetic field a 'massless' electron can acquire a mass

An international team of researchers have for the first time, discovered that in a very high magnetic field an electron with no mass can acquire a mass. 

Understanding why elementary particles e.g. electrons, photons, neutrinos have a mass is a fundamental question in Physics and an area of intense debate. This discovery by Prof Stefano Sanvito, Trinity College Dublin and collaborators in Shanghai was published in the prestigious journal Nature Communications this month.

While the applications of this discovery remain to be seen, this represents a significant breakthrough in fundamental physics. It could inspire work in high-energy physics, such as the collision experiments carried out in particle accelerators like CERN. This is the third joint publication between the group in Trinity and Prof. Faxian Xiu at Fudan University in Shanghai, who approached Prof Sanvito to provide theory support for their experimental activity based on his previous publications and international reputation in the field of theoretical physics.

Prof Stefano Sanvito, Principal Investigator at the Science Foundation Ireland funded AMBER (Advanced Materials and BioEngineering Research) centre based at Trinity and the CRANN Institute and Professor in Trinity’s School of Physics said, “This is a very exciting breakthrough because until now, nobody has ever discovered an object whose mass can be switched on or off by applying an external stimulus. Every physical object has a mass, which is a measure of the object’s resistance to a change in its direction or speed, once a force is applied. While we can easily push a light-mass shopping trolley, we cannot move a heavy-mass 6-wheel lorry by simply pushing. However, there are some examples in Nature of objects not having a mass. These include photons, the elementary particles discovered by Einstein responsible for carrying light, and neutrinos, produced in the sun as a result of thermonuclear reactions. We have demonstrated for the first time one way in which mass can be generated in a material. In principle the external stimulus that enabled this, the magnetic field, could be replaced with some other stimulus and perhaps applied long-term in the development of more sophisticated sensors or actuators. It is impossible to say what this could mean, but like any fundamental discovery in physics, the importance is in its discovery.”

He continued, “It has been very satisfying to continue to work with Prof Xiu in Shanghai. While his group are experts in growing and characterizing materials such as ZrTe5 which are very difficult to make, my group has the expertise in the theoretical interpretation. The measurements were carried out in Fudan and at the Wuhan National High Magnetic Field Center in China, while the Dublin team provided the theoretical explanation for the finding. This has been a very fruitful collaboration and we have a number of other publications in progress”.

The team studied what happened to the current passing through the exotic material zirconium pentatelluride (ZrTe5) when exposed to a very high magnetic field. Measuring a current in a high magnetic field is a standard way of characterising the material’s electronic structure. In the absence of a magnetic field the current flows easily through ZrTe5. This is because in ZrTe5 the electrons responsible for the current have no mass. However, when a magnetic field of 60 Tesla is applied (a million times more intense than the earth’s magnetic field) the current is drastically reduced and the electrons acquire a mass. An intense magnetic field in ZrTe5 transforms slim and fast electrons into fat and slow ones.

Nature communication (Open Article)

Zeeman splitting and dynamical mass generation in Dirac semimetal ZrTe5
Yanwen Liu, Xiang Yuan, Cheng Zhang, Zhao Jin, Awadhesh Narayan, Chen Luo, Zhigang Chen, Lei Yang, Jin Zou, Xing Wu, Stefano Sanvito, Zhengcai Xia, Liang Li, Zhong Wang & Faxian Xiu
Nature Communications 7, Article number: 12516 (2016)
doi:10.1038/ncomms12516

AMBER (Advanced Materials and BioEngineering Research)

Nanotechnology World Association

NASA Astronomy Picture of the Day 2016 

Aurora over Icelandic Fault 

Admire the beauty but fear the beast. The beauty is the aurora overhead, here taking the form of great green spiral, seen between picturesque clouds with the bright Moon to the side and stars in the background. The beast is the wave of charged particles that creates the aurora but might, one day, impair civilization. 

Exactly this week in 1859, following notable auroras seen all across the globe, a pulse of charged particles from a coronal mass ejection (CME) associated with a solar flare impacted Earth’s magnetosphere so forcefully that they created the Carrington Event. A relatively direct path between the Sun and the Earth might have been cleared by a preceding CME. What is sure is that the Carrington Event compressed the Earth’s magnetic field so violently that currents were created in telegraph wires so great that many wires sparked and gave telegraph operators shocks. Were a Carrington-class event to impact the Earth today, speculation holds that damage might occur to global power grids and electronics on a scale never yet experienced.

The featured aurora was imaged last week over Thingvallavatn Lake in Iceland, a lake that partly fills a fault that divides Earth’s large Eurasian and North American tectonic plates.

MICKEY MOUSE MEETS THE T-1000

Ferrofluids consist of nanoscale bits of iron, or other paramagnetic materials, suspended in a liquid, often mineral oil. People can form three-dimensional structures from a ferrofluid puddle using a magnetic field. Jessica Mehers of Lancaster University placed her ferrofluid in a glass dish and arranged several magnets underneath to sculpt this mouse shape. In case you’re wondering, yes, you can buy ferrofluid easily on the internet.

Submitted by Jessica Mehers

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The upper atmosphere of the Sun is dominated by plasma filled magnetic loops (coronal loops) whose temperature and pressure vary over a wide range. The appearance of coronal loops follows the emergence of magnetic flux, which is generated by dynamo processes inside the Sun. Emerging flux regions (EFRs) appear when magnetic flux bundles emerge from the solar interior through the photosphere and into the upper atmosphere (chromosphere and the corona). The characteristic feature of EFR is the -shaped loops (created by the magnetic buoyancy/Parker instability), they appear as developing bipolar sunspots in magnetograms, and as arch filament systems in . EFRs interact with pre-existing magnetic fields in the corona and produce small flares (plasma heating) and collimated plasma jets. The GIFs above show multiple energetic jets in three different wavelengths. The light has been colorized in red, green and blue, corresponding to three coronal temperature regimes ranging from ~0.8Mk to 2MK. 

Image Credit: SDO/U. Aberystwyth

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Very strange things happen to your body if you spend a year in space

NASA Astronaut Scott Kelly returns to Earth Tuesday night after spending almost a year in space.

But his 340 days aboard the International Space Station (ISS) haven’t been all fun and games.

Our bodies evolved on Earth, so they’re not built for weightlessness — which is exactly why NASA plans to use Kelly to study the long-term effects of spaceflight the human body.

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Earth is not the only planet in our solar system with auroras. As the solar wind–a stream of rarefied plasma from our sun–blows through the solar system, it interacts with the magnetic fields of other planets as well as our own. Saturn’s magnetic field second only to Jupiter’s in strength. This strong magnetosphere deflects many of the solar wind’s energetic particles, but, as on Earth, some of the particles get drawn in along Saturn’s magnetic field lines. These lines converge at the poles, where the high-energy particles interact with the gases in the upper reaches of Saturn’s atmosphere. As a result, Saturn, like Earth, has impressive and colorful light displays around its poles. (Image credit: ESA/Hubble, M. Kornmesser & L. Calçada, source video; via spaceplasma)

This is a manifestation of the Meissner Effect. When a superconductor reaches a critical temperature (usually very cold, 1 - 70 K) it expels all magnetic field lines. So if you place it on top of a magnet, it will float. It will float on a cushion of magnetic field. Additionally it will experience almost no friction so if you make a circular track of magnets it will levitate around it for quite a long time. And look awesome doing it. That vapour trail isn’t propulsive. It’s just how cold that superconductor is, it’s condensing the air around it.

Coronal rain

On July 19, 2012, an eruption occurred on the sun that produced a moderately powerful solar flare and a dazzling magnetic display known as coronal rain. Hot plasma in the corona cooled and condensed along strong magnetic fields in the region. Magnetic fields, are invisible, but the charged plasma is forced to move along the lines, showing up brightly in the extreme ultraviolet wavelength of 304 Angstroms, and outlining the fields as it slowly falls back to the solar surface.

Credit: NASA,SDO

This might be the most awesome combination of science and design I’ve seen: a clock created by Zelf Koelman that displays time with liquid. It’s called Ferrolic after the ferrofluid which can display recognizable shapes in response to magnets embedded inside the clock’s aluminum frame.

A ferrofluid (put together of ferromagnetic and fluid) is a liquid that becomes strongly magnetized in the presence of a magnetic field. It  was invented in 1963 by NASA’s Steve Papell as a liquid rocket fuel.

Ferrolic is controlled by an intelligent internal system that is accessible trough a web-browser. The inventor wrote in this way users can assign “the creatures” to display time, text, shapes and transitions. The clocks are more of a prototype so far, the first ones were available at a price of about $8,000 each.

see the video and more information here

During a solar flare, magnetic field lines on the sun are often visible due to the flow of plasma–charged particles–along the lines. According to theory, these magnetic lines should remain intact, but they are sometimes observed breaking and reconnecting with other lines. An interdisciplinary team of researchers suggests that turbulence may be the missing link. In their magnetohydrodynamic simulation, they found that the presence of chaotic turbulent motions made the magnetic line motion entirely unpredictable, whereas laminar flows behaved according to conventional flux-freezing theory. (Photo credit: NASA SDO; Research credit: G. Eyink et al.; via SpaceRef; submitted by jshoer)

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Solar magnetohydrodynamics

The sun is a magnetohydrodynamics (MHD) system that is not well understood. It is thought that the energy necessary to heat the corona is provided by turbulent motion in the convection zone below the photosphere, and two main mechanisms have been proposed to explain coronal heating:

The first is wave heating, in which sound, gravitational or magnetohydrodynamic waves are produced by turbulence in the convection zone. These waves travel upward and dissipate in the corona, depositing their energy in the ambient gas in the form of heat. The other is magnetic heating, in which magnetic energy is continuously built up by photospheric motion and released through magnetic reconnection in the form of large solar flares and myriad similar but smaller events—nanoflares. Currently, it is unclear whether waves are an efficient heating mechanism.

The field of MHD was initiated by Hannes Alfvén, for which he received the Nobel Prize in Physics in 1970. He described the class of MHD waves now known as Alfvén waves. Observations show that all waves except Alfvén waves have been found to dissipate or refract before reaching the corona. Current research focus has therefore shifted towards flare heating mechanisms.

The magnetic filament above erupted on April 19, 2010. The black “hair-like object” is a speck of dust on the CCD camera.

Credit: SDO/AIA

It may look like a giant ball oozing with earthworms, but it’s actually a simulation of Jupiter’s massive and complex magnetosphere — a magnetic field that extends more than four million miles from its surface.

The Earth generates a magnetic field by the convection of molten nickel-iron alloys in its outer core. Jupiter’s outer core is also thought to be responsible for its enormous magnetic field, though it is liquid hydrogen crushed by intense pressure into a metallic form that generates the magnetism rather than iron compounds. In addition, the gas giant’s surface is buffeted by powerful winds and huge storms, like the famous Great Red Spot. Scientists believe that these surface winds interact with the metallic liquid hydrogen below to stimulate some of the secondary properties of the magnetic field. 

Magnetic fields of planets compared:

(Sources 1, 2, 3

For teaching: astrophysics

Coronal loop

The corona is the outer part of the solar atmosphere. Its name derives from the fact that, since it is extremely tenuous with respect to the lower atmosphere, it is visible in the optical band only during the solar eclipses as a faint crown (corona in Latin) around the black moon disk. When inspected through spectroscopy the corona reveals unexpected emission lines, which were first identified as due to a new element (coronium) but which were later ascertained to be due to high excitation states of iron. It became then clear that the corona is made of very high temperature gas, hotter than 1 MK(megakelvin). Almost all the gas is fully ionized there and thus interacts effectively with the ambient magnetic field. It is for this reason that the corona appears so inhomogeneous when observed in the X-ray band, in which plasma at million degrees emits most of its radiation. In particular, the plasma is confined inside magnetic flux tubes which are anchored on both sides to the underlying photosphere. When the confined plasma is heated more than the surroundings, its pressure and density increase. Since the tenuous plasma is optically thin, the intensity of its radiation is proportional to the square of the density, and the tube becomes much brighter than the surrounding ones and looks like a bright closed arch: a coronal loop.

Credit: Fabio Reale