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Category: physics – Page 201

Today, the greatest mysteries facing astronomers and cosmologists are the roles gravitational attraction and cosmic expansion play in the evolution of the Universe.

To resolve these mysteries, astronomers and cosmologists are taking a two-pronged approach. These consist of directly observing the cosmos to observe these forces at work while attempting to find theoretical resolutions for observed behaviors – such as dark matter and dark energy.

In between these two approaches, scientists model cosmic evolution with computer simulations to see if observations align with theoretical predictions. The latest of which is AbacusSummit, a simulation suite created by the Flatiron Institute’s Center for Computational Astrophysics (CCA) and the Harvard-Smithsonian Center for Astrophysics (CfA).

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If you think of very low temperatures, there’s a good chance you are picturing ice. Ice is a quintessential “cold” thing for us. But at extreme pressures, like in the core of large planets, something peculiar can happen. Ice can remain solid but have a temperature hotter than the surface of the Sun.

This type of water ice is called “superionic ice” and has been added to the list of around 20 phases water can structurally form, including ice, liquid, and vapor. Now, researchers report in Nature Physics the discovery and characterization of two superionic ice phases, having found a way of reliably and stably recreating the ice for longer than has previously been achieved to be able to study it.

One superionic phase extends between 200,000 and 60,000 times the atmospheric pressure at sea level and at a temperature of several hundred to over 1,000 ° C. The other phase extends to half the pressure experienced at the center of the Earth and with temperatures of thousands of degrees.

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Scientists have released the largest catalog of gravitational wave detections to date, shedding new light on interactions between the most massive objects in the universe, black holes and neutron stars.

The catalog was compiled by three groundbreaking detectors: the two Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors located in Hanford, Washington, and Livingston, Louisiana, and the European Virgo gravitational wave antenna in Pisa, Italy.

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Of the cosmos’ four fundamental forces, gravity is the one that grasps us even before we exit the womb. From our first few minutes of life until we lose the fight to lift our heads from death’s pillow, this weakest of nature’s fundamental forces continues to elude researchers.

In the last few years, however, gravitational wave astronomy has made great strides in detecting gravitational radiation rippling through spacetime at the speed of light.

Einstein first predicted that any accelerating mass should emit gravitational radiation in the form of waves. Gravitational waves were first indirectly detected almost 20 years ago. But it was only recently, in 2,015 that the ground-based LIGO (Laser Interferometer Gravitational-wave Observatory) detected waves from two merging stellar mass black holes over a billion light years distant in the general direction of the Southern Hemisphere’s Magellanic Clouds.

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A team of international scientists, including researchers from The Australian National University (ANU), have unveiled the largest number of gravitational waves ever detected.

The discoveries will help solve some of the most complex mysteries of the Universe, including the building blocks of matter and the workings of space and time.

The global team’s study, published on ArXiv, made 35 new detections of gravitational waves caused by pairs of merging or neutron stars and black holes smashing together, using the LIGO and Virgo observatories between November 2019 and March 2020.

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In a new report now published in Science, primary authors Zhen Zhu, Michal Papaj, and an international research team in physics, materials science, and condensed matter at the Jiao Tong University, China, Massachusetts Institute of Technology, U.S., and the Chinese Academy of Sciences discovered the Fermi surface of supercurrent-induced quasiparticles in a superconducting system for the first time. This discovery comes 50 years after the initial theoretical prediction was made by physicist Peter Fulde and revealed the impact of the finite Cooper pair momentum on the quasiparticle spectrum. In condensed matter physics, Cooper pairs are a pair of electrons with opposite spins loosely bound due to electron-lattice interactions. Superconductivity is based on their condensation to Bosonic states at low temperatures. The interplay of superconductivity and magnetic fields leads to the phenomenon of a ‘segmented Fermi surface. A leading author of this work, MIT Professor of Physics Liang Fu, outlined the significance of this discovery.

Supercurrent flow in a superconductor

Physicists assume that a sufficiently large supercurrent can close the energy gap in a superconductor and create gapless quasiparticles via the Doppler shift of quasiparticle energy. This is facilitated by the finite momentum of Cooper pairs in the presence of supercurrent flow in a superconductor, where the shift in Cooper pair momentum can result in a Doppler shift. In this work, Zhu et al. used quasiparticle interference to image the field-controlled Fermi surface of bismuth telluride (Bi2Te3) thin films proximitized by the superconductor niobium diselenide (NbSe2). A small applied in-plane magnetic field induced a screening supercurrent, which led to finite momentum pairing on the topological surface states of Bi2Te3. The scientists identified distinct interference patterns to indicate a gapless superconducting state with a segmented Fermi surface to reveal the strong impact of the finite Cooper pair momentum on the quasiparticle spectrum.

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