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Shear-induced structural transitions happen when the structure of a material changes due to the application of force. It’s a phenomenon observed in various systems, including metals like aluminium and iron, molecular crystals such as ice and quartz, and even the Earth’s mantle.

A better understanding of how it works could lead to an improvement in the processing and fabrication of materials with more control on defect formation.

Measuring microscopic processes like this is usually challenging because electron microscopy cannot resolve individual atoms’ motions in bulk solids, and the strong shear force makes things especially difficult.

Here, the researchers used colloidal crystals, allowing them to observe transitions at the single-particle level. As a soft material (one that can easily be deformed), colloid crystals are particularly well-suited for this type of study.

They found that under certain conditions, a liquid layer formed around the growing new crystal structure. This phenomenon is known as “virtual melting” because it occurs well below the effective melting temperature. This liquid layer facilitates the transition by reducing the strain energy at the interface between the old and new crystal structures.

Virtual melting has been proposed in theory and simulation, but had never been directly observed in experiments before. The team’s results not only represent the first experimental observation of this process but also help us to better understand under what circumstances it takes place.

The study has potential applications across various fields, including metallurgy, materials science, and geophysics. The concept of virtual melting could also provide new a new way of thinking about stress relaxation and phase transitions in other systems.

Protons and neutrons in atomic nuclei are themselves made up of fundamental particles known as quarks. These quarks are held together by the strong interaction via force carriers called gluons.

When heavy atomic nuclei collide at high energies close to the speed of light, these constituent particles can break free from each other. The resulting substance, called a quark–gluon plasma, exhibits collective flowlike behaviour much like an everyday liquid.  Unlike a normal viscous liquid however, these near-perfect fluids lose very little energy as they flow.

Researchers are very interested quark–gluon plasmas because they filled the entire Universe just after the Big Bang before matter as we know it was created.

The CMS Collaboration of scientists at CERN routinely create this state of matter for a very brief moment by colliding large nuclei with each other.  In this paper, the researchers used sound waves as a way of understanding the plasma’s fundamental properties.

Sound is a longitudinal wave that produces compressions and rarefactions of matter in the same direction as its movement. The speed of these waves depends on the medium’s properties, such as its density and viscosity. It can, therefore, be used as a probe of the medium.

The team were able to show that the speed of sound in their quark–gluon plasma was nearly half the speed of light – a measurement they made with record precision compared to previous studies.

The results will help test our theories of the fundamental forces that hold matter together, allowing us to better understand matter in the very early Universe as well as future results at particle colliders.

Astronomers studying the night sky from the Southern Hemisphere have uncovered a supernova — the powerful explosion of a star — that appears to detonated twice. The unique discovery of the double-detonation supernova comes as two smaller nova explosions have caused stars to suddenly become visible to the naked eye.

A supernova, according to NASA, is an extremely bright, super-powerful explosion of a star and the biggest explosion that humans have ever seen. Astronomers uncovered the rare double-detonation supernova by studying a “cosmic bubble” — known as a supernova remnant — called SNR 0509-67.5. It’s 23 light-years across and expanding at over 11 million miles per hour. It’s previously been imaged by NASA’s Hubble Space Telescope.

SNR 0509-67.5 is in the Large Magellanic Cloud, a dwarf galaxy that orbits the Milky Way about 160,000 light-years distant in the constellation Dorado. SNR 0509-67.5 is Type Ia supernovae, which are known to produce iron on Earth, including in blood. Understanding these explosions of white dwarf stars is critical to astronomers who use them to measure distances in space.

How A Supernova Exploded Twice

SNR 0509-67.5 is a Type Ia supernova, the result of two stars orbiting each other. One, a white dwarf star — the dense core of a dead sun-like star — sucks matter onto its surface from the other star until a thermonuclear explosion occurs. The new discovery of a double-detonation supports the theory that, in at least some Type Ia supernovae, the white dwarf can be covered by a bubble of helium that, when it ignites, causes a shockwave that triggers a second detonation in the core of the star.

Astronomers predicted that if a double detonation had occurred, the remnant of the supernova would contain two separate shells of calcium. That’s exactly what was observed using the European Southern Observatory’s Very Large Telescope in Chile. The discovery was published today in Nature Astronomy.

Hubble Spots A Supernova

Earlier this year, NASA’s Hubble Space Telescope imaged a supernova about 600 million light-years away in the constellation Gemini. Visible as a blue dot at the center of the image above, supernova SN 2022aajn is also a Type Ia supernova. Exactly these types of supernovae are useful for astronomers because they all have the same intrinsic luminosity. That means they can be used as beacons to measure the distance to faraway galaxies.

ForbesA ‘New Star’ Suddenly Got 3 Million Times Brighter — How To See ItBy Jamie Carter

Background

Although they fall into the category of smaller explosions called a nova, two exploding stars are currently visible in the night sky. V572 Velorum, in the constellation Vela and V462 Lupi, in the constellation Lupus — only visible from the Southern Hemisphere — are currently shining millions of times brighter than usual.

Later this year or next year, if predictions are correct, a star in the Northern Hemisphere called T Coronae Borealis (T CrB and “Blaze Star”) in the constellation Corona Borealis will explode and become visible to the naked eye for several nights. This star system, about 3,000 light-years away, is a recurrent nova, meaning it experiences predictable eruptions. The last time T CrB brightened noticeably was in 1946.

Wishing you clear skies and wide eyes.