Hierarchical Merging: Black Holes' Past Lives

Some merging black holes may be second-generation black holes that formed from the previous merging of two smaller black holes, according to a new study. Pictured is an artist’s concept of the hierarchical formation of black holes.
Image Credit: LIGO/Caltech/MIT/R. Hurt (IPAC)
(CC BY-NC-ND 3.0)

Scientific Frontline: Extended "At a Glance" Summary: Hierarchical Black Hole Mergers

The Core Concept: Hierarchical merging is an alternative black hole formation pathway wherein a massive black hole is created not from a dying star, but from the collision and merging of two smaller, previously formed black holes.

Key Distinction/Mechanism: Unlike first-generation black holes formed by stellar collapse—which lose most of their angular momentum and possess very little spin—second-generation black holes spin rapidly. When a highly spinning second-generation black hole merges again, it causes the system's orbital plane to wobble, or precess, just before the collision.

Major Frameworks/Components: 

• Gravitational Wave Transient Catalog 4.0 (GWTC-4.0): The dataset used to identify the characteristic orbital wobble signatures across 155 binary black hole pairs.
• Angular Momentum and Spin: The physical properties used to distinguish low-spin, star-born black holes from rapid-spin, merger-born black holes.
• Orbital Precession: The wobbling effect in a binary system's orbital plane caused by the misaligned, rapid spins of second-generation black holes.
• Stellar Evolution Theory: The standard framework predicting that supernovas cannot leave behind black holes larger than 45 solar masses, making hierarchical merging a necessary model to explain the existence of more massive black holes.

Ultrafast Optical Beam Steering Chip

Caltech researchers created a chip that uses a patterned beam of light to modify the optical properties of a meta-material. A second beam can then pass through the material and get deflected according to the first beam's projected pattern.
Image Credit: Claudio Hail

Scientific Frontline: Extended "At a Glance" Summary: Ultrafast All-Optical Beam Steering

The Core Concept: Researchers have developed a novel photonic device utilizing an optical meta-surface that redirects a beam of light using a second light beam in merely 74 femtoseconds (74 quadrillionths of a second).

Key Distinction/Mechanism: Traditional optical chips modulate light by altering a material's electronic properties, a process fundamentally bottlenecked by the time required for electrons to relax to lower energy states. This new approach bypasses electronic relaxation by leveraging the optical Kerr effect, employing a patterned "pump" beam to momentarily alter the refractive index of a meta-surface, which instantly deflects a weaker "probe" beam.

Major Frameworks/Components:

• Optical Meta-surfaces: Ultrathin sheets of amorphous silicon patterned with nanoscale pillars smaller than the wavelength of the light, specifically designed to trap and recirculate photons to amplify interaction strength.
• Optical Kerr Effect: A phenomenon in which an intense beam of light alters the motion of electrons within their orbitals, briefly changing the material's refractive index without exciting the electrons into longer-lived energy states.
• Pump-Probe System: An intense, patterned light beam (the pump) modulates the optical properties of the material, while a secondary beam (the probe) passes through and is steered by the resulting modifications.

Tumbleweed: The First Artificial Protein Motor

Tumbleweed stands with two of its three feet attached to a DNA strand, with each foot binding to a specific DNA sequence. By adding or removing molecules that control which feet can bind, the protein motor can be guided on a walk along the DNA strand.
Illustration Credit: Courtesy of the research group

Scientific Frontline: Extended "At a Glance" Summary: Artificial Protein Motor "Tumbleweed"

The Core Concept: An international research team has engineered "Tumbleweed," an artificial protein motor capable of taking externally controlled, directed steps along a DNA track to mimic the biological engines found inside living cells.

Key Distinction/Mechanism: Unlike previous molecular machines constructed from synthetic molecules or DNA, or static AI-designed proteins, Tumbleweed is built entirely from complex protein components. It navigates by alternating three distinct "feet" that bind to specific DNA sequences; researchers direct its movement by modifying the surrounding chemical environment to control which feet attach to the track..

Major Frameworks/Components:

• Tumbleweed Protein Motor: A dynamic, engineered protein structure featuring three distinct binding appendages, or "feet."
• DNA Track: A structured nucleic acid pathway containing specific sequences that correspond to the motor's feet.
• Chemical Environment Control: A mechanism where the addition or removal of specific molecules triggers the binding and unbinding of the feet, forcing the motor to take a step.
• Biological Analogs: Modeled after naturally occurring motor proteins such as myosin, which powers muscle contraction and cell division, and kinesin, which transports intracellular signaling molecules.

Brain-Inspired Oxide Electronics for AI

Novel components based on an oxide interface, developed by researchers at the ctd.qmat Cluster of Excellence in Würzburg, electronically replicate central functions of neural networks and open up new perspectives for energy-efficient hardware.
Image Credit: Jochen Thamm, think-design

Scientific Frontline: Extended "At a Glance" Summary: Neuromorphic Oxide-Interface Electronics

The Core Concept: A novel class of polymorphic electronic devices utilizes complex oxide materials to emulate the neural structure of the human brain, allowing hardware to process and store information simultaneously.

Key Distinction/Mechanism: Unlike traditional computing architecture that spatially separates processing and memory, this technology uses an ultrathin, conductive quasi-two-dimensional electron gas formed between two insulating oxides. Electrical currents displace oxygen atoms, altering electrical resistance and allowing the device to learn and adapt based on past activity, a process closely mimicking synaptic neuroplasticity.

Major Frameworks/Components:

• Lanthanum aluminate (\(\text{LaAlO}_3\)) and strontium titanate (\(\text{SrTiO}_3\)): The two insulating complex oxides that combine to create a highly conductive interface.
• Polymorphic nanoscale architecture: A single device that can function variably as a transistor (for current switching), a memristor (for resistance-based memory), and a memcapacitor (for electrical history-dependent capacitance).
• Quasi-two-dimensional electron gas: Microscopic electronic pathways that enable the precise, targeted control of charge carrier transport.

Quantum Control via Carbon Nanotori

The doughnut-shaped carbon molecule develops stable toroidal moments when an electric voltage is applied. The image shows the distribution of the corresponding electron density.
Image Credit: AG Berakdar

Scientific Frontline: Extended "At a Glance" Summary: Quantum Control via Carbon Nanotori

The Core Concept: Researchers have discovered a method to generate and control toroidal moments—a rare class of electromagnetic dipoles—at the nanoscale using doughnut-shaped rings of carbon atoms known as nanotori.

Key Distinction/Mechanism: Unlike standard electric or magnetic dipoles, toroidal systems enclose a magnetic field but remain electrically neutral, generating no external electric or magnetic fields. By applying a constant electric field to carbon nanotori, electrons are forced into a 3D vortex around the ring, generating a stable, loss-free toroidal moment that overcomes the energy dissipation of conventional, macroscopic toroidal coils.

Major Frameworks/Components:

• Toroidal Dipoles: A third, traditionally elusive class of charge-current distributions alongside conventional electric and magnetic dipoles.
• Carbon Nanotori: Doughnut-shaped nanoscale carbon structures that host the requisite electron vortices.
• Quantum Mechanical Phases: The underlying physical states that these localized toroidal moments can directly alter without producing stray fields.

Superconductivity in Quantum Materials Under Pressure

The quantum material tantalum disulfide has paradoxical properties: it consists of layers, one of which becomes superconducting upon cooling while the other acts as an insulator. Under pressure, this interplay changes – and the material becomes superconducting at temperatures roughly three times higher.
Image Credit: © Studio HübnerBraun

Scientific Frontline: Extended "At a Glance" Summary: Quantum Materials Under Pressure

The Core Concept: Applying high pressure to the quantum material tantalum disulfide dramatically increases the temperature at which it achieves superconductivity and fundamentally alters the nature of its superconducting state.

Key Distinction/Mechanism: Unlike under standard atmospheric conditions where insulating atomic layers disrupt the process, immense pressure compresses the crystal layers of tantalum disulfide. This physical squeezing brings superconducting layers into closer contact, releases electrons from the insulating layer, and enables a robust, three-dimensional superconductivity with a sevenfold increase in participating electrons.

Major Frameworks/Components:

• Muon Spin Spectroscopy: The use of muons—heavy, unstable elementary particles—as highly sensitive microscopic probes to investigate the magnetic fields and superconducting properties within the material.
• Crystal Lattice Compression: The physical mechanism of squeezing the atomic layers of tantalum disulfide with pressures hundreds of times greater than a car tire to overcome insulating barriers.
• Altered Electron Pairing: The pressure-induced shift in how electrons pair up and move together through the material, resulting in a more robust superconducting state.

Programmable Thermal Radiation Explained

New device enables flexible control of heat
Heat is absorbed from the right, heating the structure, where it is radiated to the left, cooling the structure.
Image Credit: Osaka Metropolitan University

Scientific Frontline: Extended "At a Glance" Summary: Programmable Thermal Radiation

The Core Concept: Programmable thermal radiation refers to the ability to independently control the absorption and emission of heat, allowing thermal energy to be directed, switched on and off, and stored like data in a microchip. This circumvents the traditional thermodynamic rule of reciprocity, which dictates that a material must absorb and emit heat symmetrically.

Key Distinction/Mechanism: Unlike conventional materials that exhibit reciprocal thermal behavior, this new device separates absorption and emission by combining magneto-optical materials with a phase-change material known as GST. This integration allows the material to absorb heat from one direction and emit it in another even at near-normal angles of incidence, while retaining its thermal state without continuous electrical power.

Major Frameworks/Components:

• The Reciprocity Principle: The fundamental thermodynamic limitation being bypassed, which normally links a surface's efficiency in absorbing heat at a specific wavelength and direction to its emission.
• Magneto-Optical Materials: Substances manipulated by an external magnetic field to alter their interaction with light, allowing the separation of thermal absorption and emission behaviors.
• Phase-Change Material (GST): A specialized compound integrated into the device that acts as a switch and a memory cell, enabling the system to "remember" its thermal configuration after power is disconnected.
• Metagratings: The structural nanoscale architecture used to achieve nonreciprocity at near-normal incidence, overcoming the limitations of previous devices that required extreme, highly inefficient angles of incoming light.

Understanding the Physical Upper Limit of Viscosity

Scientific Frontline: Extended "At a Glance" Summary: Viscosity Upper Limit

The Core Concept: Researchers have identified a practical upper bound for material viscosity, estimated at \(10^{30 \pm 2}\) Pa s, beyond which substances function as essentially rigid bodies over finite timescales.

Key Distinction/Mechanism: Unlike classical assumptions of infinite viscosity for solid materials, this study establishes a finite quantitative threshold determined by the convergence of geodetic, experimental, and numerical simulation data.

Major Frameworks/Components:

• Geodetic observations of tectonic plate stability.
• Laboratory-derived flow laws for major rock-forming minerals, including olivine, clinopyroxene, diopside, anorthite, and quartz.
• Numerical simulations of mantle convection and visco-elasto-brittle deformation.

Little Red Dots and Cosmic Neutrinos

At the center of the Little Red Dot, there may be a black hole surrounded by a thick outer gaseous envelope. In this environment, photons produced near the center are absorbed and scattered by the gas, so neutrinos can escape the envelope without interacting with the surrounding gases. If there are many Little Red Dots, they may account for a part of the high-energy neutrinos arriving from the universe.
 Image Credit: KyotoU / Riku Kuze

Scientific Frontline: Extended "At a Glance" Summary: Little Red Dots as Hidden Neutrino Sources

The Core Concept: "Little Red Dots" are abundant, high-redshift, small red galaxies recently observed by the James Webb Space Telescope. Researchers hypothesize that these galaxies harbor growing supermassive black holes enveloped in dense gas, making them a primary candidate for the universe's mysterious all-sky high-energy neutrino background.

Key Distinction/Mechanism: High-energy neutrinos are produced when accelerated particles collide with surrounding matter or photons. Unlike typical high-energy neutrino sources, which also emit detectable gamma rays, the dense gaseous envelopes surrounding the black holes in Little Red Dots suppress gamma-ray emissions while allowing neutrinos to escape, thereby matching observed cosmic background levels.

Major Frameworks/Components:

• Supermassive Black Holes: Central celestial objects generating the extreme energetic forces required for particle collisions.
• Particle Acceleration: The mechanism by which protons and other particles achieve high velocities within buried jets, leading to the production of secondary particles.
• Gaseous Envelopes: Thick, dense layers of gas surrounding the central black hole that absorb scattered photons (gamma rays) while permitting electrically neutral neutrinos to escape.
• Neutrino Spectrum Analysis: Complex numerical modeling utilized to evaluate cooling processes, particle collisions, and the expected neutrino output from these distant galaxies.

AI Unlocks New Superconductors

\(\mathrm{YRu}_3\mathrm{B}_2\) and \(\mathrm{Lu}_3\mathrm{B}_2\) gain their superconductivity from electrons forming flat bands in a kagome lattice, named after a hexagonal Japanese basket-weaving pattern.
Photo Credit: Esa Kapila

Scientific Frontline: Extended "At a Glance" Summary: Machine Learning in Superconductor Discovery

The Core Concept: Researchers have utilized machine-learning algorithms to identify two new superconductive materials, \(\mathrm{YRu}_3\mathrm{B}_2\) and \(\mathrm{Lu}_3\mathrm{B}_2\), demonstrating a novel methodology to rapidly filter practically infinite elemental combinations. The superconductivity of these materials arises from electrons forming flat bands within a specific geometric atomic structure.

Key Distinction/Mechanism: Unlike traditional superconductor discovery, which has historically relied on serendipity or computationally exhaustive processes, this new framework deploys a machine-learning-based pre-screening process to filter billions of candidates before executing targeted calculations and physical synthesis.

Major Frameworks/Components: 

• Machine-Learning Pre-screening: Advanced algorithms capable of computationally processing and filtering billions of potential elemental combinations to find viable material candidates.
• Quantum Geometry: The theoretical and mathematical foundation used to model the quantum properties and viability of the pre-screened combinations.
• Kagome Lattice: A distinct structural atomic arrangement, mirroring a traditional Japanese hexagonal basket-weaving pattern, that facilitates the flat electron bands necessary for superconductivity in \(\mathrm{YRu}_3\mathrm{B}_2\) and \(\mathrm{Lu}_3\mathrm{B}_2\).

Manganese Spintronics: Light-Switched Data Storage

A coin-sized area of the new material is illuminated through a mask: The spins change their state, and the material changes color.
Illustration Credit: ©: Katja Heinze / JGU

Scientific Frontline: Extended "At a Glance" Summary: Switching Spin States in Manganese Ions

The Core Concept: Researchers have synthesized a novel manganese-based molecular material that allows for the stable switching of electron spin states using light, functioning as a highly compact data storage device.

Key Distinction/Mechanism: Unlike traditional iron-containing molecular memory devices that max out at temperatures around 130 Kelvin, this new material utilizes manganese. By combining manganese ions with N-heterocyclic carbene ligands, the strong chemical bond stabilizes the low-spin state and creates a high energy barrier. When irradiated with light, the electrons change spin states (shifting the material's color from dark red to light yellow), and thes magnetic data persists at higher temperatures (approximately minus 132 degrees Celsius) even after the light source is removed.

Major Frameworks/Components:

• Spintronics: The study and exploitation of the intrinsic spin of the electron and its associated magnetic moment for solid-state devices.
• Binary Spin States: The alignment of individual electron spins in either a parallel (high-spin) or antiparallel (low-spin) configuration, acting as digital "1s" and "0s."
• N-Heterocyclic Carbene Ligands: Specific chemical ligands used to bind strongly to the manganese ions, thereby widening the energy barrier between the distinct spin states.
• Photomagnetic Relaxation/Switching: The mechanism by which incoming light is utilized to physically alter the electron spin states and write digital information into the material.

Automated Semiconductor Defect Detection

Rice doctoral alumna Tia Gray holding a sample of selectively grown diamond microstructure in the shape of an owl.
Photos Credit: Brandon Martin/Rice University

Scientific Frontline: Extended "At a Glance" Summary: Automated Defect Detection in Advanced Semiconductors

The Core Concept: Materials scientists have developed a custom, Python-based software workflow to rapidly analyze high-resolution X-ray diffraction data, successfully measuring microscopic defects in diamond and other wide-bandgap semiconductors.

Key Distinction/Mechanism: Rather than relying on time-consuming and labor-intensive manual analysis, this approach utilizes automated software to process X-ray diffraction patterns. It rapidly identifies structural irregularities and calculates the precise density of atomic lattice dislocations across diverse crystal structures.

Major Frameworks/Components:

• High-resolution X-ray diffraction (HRXRD) analysis.
• Custom Python-based automation and data processing software.
• Lattice dislocation density calculation modeling.
• Wide-bandgap semiconductor evaluation protocols (specifically focusing on synthetic single-crystal diamond and gallium nitride).

Janus 2D Semiconductors: Synthesis Physics Solved

An image of the Janus formation reaction in which the outermost chalcogen atom in an atomic layer material is replaced by another chalcogen atom with the support of electron accumulation.
Image Credit: ©Toshiaki Kato

Scientific Frontline: Extended "At a Glance" Summary: Janus Two-Dimensional Semiconductors

The Core Concept: Janus two-dimensional (2D) semiconductors are asymmetrical materials featuring top and bottom surfaces composed of different elements. This structural asymmetry generates a robust internal electric field, making the materials highly reactive and versatile for technological applications.

Key Distinction/Mechanism: While atom substitution traditionally requires immense heat, Janus materials can be synthesized efficiently at room temperature via plasma treatment. The mechanism relies on electrons from the plasma accumulating at the interface between the 2D material and its substrate, which weakens chemical bonds and significantly lowers the activation energy required for the selective replacement of top-layer chalcogen atoms.

Major Frameworks/Components:

• In-Situ Optical-Electrical Measurement: A newly developed monitoring system utilized to observe structural and electrical changes in real time during plasma treatment.
• The Electron Accumulation Model: A theoretical framework demonstrating that excess accumulated electrons at the substrate interface drive the room-temperature substitution process.
• Ultraviolet Light Acceleration: The application of UV light to increase electron accumulation, a process shown to accelerate the substitution reaction by more than twofold.
• First-Principles Calculations: Computational methods utilized to successfully validate the electron accumulation theory and formalize the predictable synthesis model.

Quantum Mechanics Without Imaginary Numbers

Explanatory diagram for the research question – is quantum mechanics possible with only real numbers? – and results of the study.
Image Credit: © HHU / Pedro Barrios Hita

Scientific Frontline: Extended "At a Glance" Summary: Real-Number Quantum Mechanics

The Core Concept: Quantum mechanics, the physical theory describing the behavior of atomic and subatomic particles, can be successfully formulated using solely real numbers. This mathematically rigorous alternative challenges the traditional reliance on complex numbers, which incorporate both real and imaginary components, to describe quantum states.

Key Distinction/Mechanism: Standard quantum mechanics uses complex numbers where a state's amplitude is represented by the real part and its phase by the imaginary part. By utilizing a physically motivated, less restrictive postulate for system composition, researchers have developed an alternative framework that strictly uses real numbers while remaining experimentally indistinguishable from standard quantum mechanics.

Origin/History: The development of quantum mechanics began in the 1900s through the foundational work of physicists such as Max Planck, Niels Bohr, Werner Heisenberg, and Erwin Schrödinger. The modern debate over the mathematical necessity of imaginary numbers was highlighted by a 2021 study declaring them essential, which was subsequently overturned in 2026 by physicists from Heinrich Heine University Düsseldorf and the German Aerospace Center.

Limnology: In-Depth Description

Photo Credit: Claudia Chiavazza

Limnology is the comprehensive scientific study of inland aquatic ecosystems, focusing on both natural and man-made bodies of water. This discipline encompasses lakes, reservoirs, ponds, rivers, streams, wetlands, and groundwater. The primary goal of limnology is to understand the complex interactions between the physical, chemical, and biological components of these ecosystems, elucidating how they function, how they change over time, and how they respond to environmental stressors and human activities.

Biophotonics: In-Depth Description

Biophotonics is the interdisciplinary applied science of generating, manipulating, and utilizing photons to image, identify, and engineer biological materials at the molecular, cellular, and tissue levels. The primary goal of this field is to harness the unique properties of light to non-invasively probe biological functions, detect diseases in their nascent stages, and develop targeted therapeutic interventions without compromising the structural integrity of the living systems under investigation.

Dark Matter & Galactic Center Excess

An image of the excess of gamma rays that occurs at the center of our Milky Way superimposed with an optical image of the galaxy. The cause of this excess and whether it could have come from dark matter has been debated for over a decade.
Image Credit: NASA Goddard/A. Mellinger (Central Michigan Univ.) and T. Linden (Univ. of Chicago).

Scientific Frontline: Extended "At a Glance" Summary: Galactic Center Excess and Dark Matter

The Core Concept: The Galactic Center Excess (GCE) is an unexplained, roughly spherical glow of massive gamma-ray emissions originating from the center of the Milky Way galaxy.

Key Distinction/Mechanism: While previous models leaning toward stellar sources lacked individual photon energy data, a newly developed machine-learning method incorporates this spectral information. The analysis reveals that if the GCE is caused by neutron stars, there must be at least 35,000 extremely faint sources, making their collective signal nearly indistinguishable from self-annihilating dark matter.

Major Frameworks/Components:

• Self-Annihilating Dark Matter: A theoretical model postulating that dark matter particles collide and destroy one another, producing the detectable gamma-ray glow.
• Millisecond Pulsars: The primary alternative hypothesis attributing the excess radiation to a massive, unresolved population of rapidly spinning, dense neutron stars.
• Machine-Learning Spatial-Spectral Analysis: A novel computational framework trained on over a million simulated observations to simultaneously evaluate spatial data and individual photon energies.

Computational Chemistry: In-Depth Description

Computational chemistry is a vital sub-discipline of chemical science that leverages advanced mathematical algorithms, computer software, and theoretical physics to simulate, predict, and analyze molecular structures, dynamic behaviors, and material properties. Its primary goal is to translate the fundamental laws of quantum and classical mechanics into functional computational models. By doing so, it allows scientists to explore complex chemical phenomena that may be too rapid, hazardous, or challenging to observe directly in a laboratory setting, while also guiding experimentalists toward promising discoveries prior to physical synthesis.

Hardy Ice Plant Optics: Biomimetic Materials

Petals that Reflect: Parabolic Surface Structures in the Hardy Ice Plant
Microscopic parabolic ridges in the hardy ice plant’s petals create a natural glossy effect by controlling light reflection.
Image Credit: Professor Hiroshi Moriwaki from Shinshu University, Japan

Scientific Frontline: Extended "At a Glance" Summary: Biomimetic Optics of the Hardy Ice Plant

The Core Concept: The hardy ice plant (Delosperma cooperi) possesses microscopic parabolic surface grooves on its petals that manipulate light to produce a striking, pigment-free glossy appearance. This structural optic phenomenon allows the plant to scatter and directionally reflect light across a broad range of viewing angles.

Key Distinction/Mechanism: Unlike plants that generate gloss through thin-film interference, surface waxes, or prism-like structures, the hardy ice plant utilizes a specialized parabolic surface architecture. The front surface of the petal broadly scatters light akin to a traffic mirror, while the back surface concentrates light that has passed through the upper layer.

Major Frameworks/Components:

• Structural Coloration: The principle that physical microscopic geometries, rather than chemical pigments or waxes, dictate optical behaviors like light reflection, absorption, and scattering.
• Advanced Metrology: The employment of scanning electron microscopy (SEM), confocal laser microscopy, and angle-dependent reflectance measurements to isolate and map the parabolic geometries.
• Biomimetic Replication: The use of silicone molds and UV-curable resin to synthetically reproduce the petal's biological optical architecture for materials testing.

Macroscopic Quantum Entanglement Explained

Proof of quantum effects in a strange metal
Image Credit: © TU Wien / Harald Ritsch

Scientific Frontline: Extended "At a Glance" Summary: Macroscopic Quantum Entanglement (Schrödinger's Anthill)

The Core Concept: For the first time, physicists have detected a high degree of multipartite quantum entanglement within a macroscopic, centimeter-sized crystal of a "strange metal." This demonstrates that massive objects made of countless particles can collectively exhibit fundamental quantum effects.

Key Distinction/Mechanism: Rather than attempting to force an entire object into a superposition state (akin to the theoretical Schrödinger's cat), researchers measured the material's sensitivity to neutron bombardment. Using a metric called quantum Fisher information, they found that the material responds to disturbances collectively—much like a disturbed anthill—with groups of at least nine particles acting as single, quantum-entangled entities rather than independent atoms.

Major Frameworks/Components:

• Quantum Fisher Information: A theoretical tool from quantum information science used to quantify the sensitivity of a many-body system to external changes, directly indicating its degree of entanglement.
• Strange Metals: A complex class of materials (in this experiment, a crystal of cerium, palladium, and silicon) known for highly unusual quantum properties, such as suppressing electrical current fluctuations.
• Neutron Scattering: An experimental technique where neutrons are fired at the crystal to observe the transfer of energy and measure the resulting collective particle response.