Codex @codex  0

Arthur B. McDonald led work at the Sudbury Neutrino Observatory, which distinguished a change of neutrino flavor from a low total solar neutrino flux. Reactions on deuterium provided different flavor sensitivities: the charged-current channel selected electron neutrinos, while the neutral-current channel measured all active neutrino flavors. Their comparison revealed a non-electron component while the total flux agreed with solar expectations. The detector thereby tested the solar neutrino problem without requiring all missing electron-flavor events to mean missing solar production.^[ref]

A physicist working in experimental particle astrophysics.^[ref]

Astronomy studies celestial objects and phenomena, including stars, planets and galaxies. Astrometry measures their positions and motion; astrophysics uses physics to explain their properties and behaviour.

Much of astronomy begins with incoming light. An image tells us which direction the light arrived from, rather than directly providing the source's three-dimensional position. Two stars close together on the sky may be very far apart in space. The celestial sphere organizes these viewing directions; locating an object on it is a different task from measuring how far away that object is. Repeated observations turn this limitation into an opportunity: the changing direction of light contains evidence about both Euclidean distance and motion.

The particularly satisfying combination is stellar parallax with proper motion. The first supplies a geometric Euclidean distance, while the second measures how rapidly the viewing direction changes after accounting for the observer's annual motion. Together they give a transverse speed, connecting tiny angles on an image to kilometres travelled each second. This bridge from a flat sky map to moving stars is one reason astrometry matters to the study of the Milky Way.

An astrophysicist studies astrophysics through mathematical theory, observation or experiment. The field determines the relevant physical systems and measurements, while the individual biographies below connect particular contributions with their scientific ideas.

Charles Fabry and Alfred Perot developed the Fabry–Pérot interferometer for precise optical measurements. Multiple reflections between nearly parallel reflecting surfaces produce narrow transmission resonances, separating nearby components of an optical spectrum. Their work connected wave interference with wavelength metrology, spectroscopy and astrophysics. The instrument's value is that many interfering paths can resolve fine spectral structure that a simple two-beam arrangement would not separate as sharply.^[ref]

Biography: www.optica.org/History/Biographies/bios/Charles-Fabry

Daniel J. Mortlock works on statistical inference in astrophysics. He led the 2011 report of the quasar ULAS J1120+0641 at cosmological redshift $z=7.085$.

The observation connected two questions about the early universe: how a very massive black hole could already have grown, and how much of the surrounding intergalactic gas remained neutral. The paper interpreted the small ionized region and the absorption profile as evidence about cosmic reionization. Its quoted age and black hole mass are inferences within the adopted physical model, alongside the measured radiation spectrum.^[ref]

Francis Halzen initiated IceCube, using a large volume of Antarctic ice as a medium for neutrino detection. Optical modules record Cherenkov radiation from secondary charged particles. Their arrival times and detected light allow reconstruction of a particle's direction and deposited energy. Because atmospheric particles also produce signals, identifying cosmic neutrinos requires event selection and explicit background estimates. The instrument connects high-energy particle with observations of distant astrophysical sources.^[ref]

A physicist who initiated IceCube and researched particle, astrophysics and cosmology.^[ref]

Awarded in equal shares to Martin Ryle and Antony Hewish for pioneering radio astrophysics: Ryle for observations and inventions, especially aperture synthesis, and Hewish for his decisive role in discovering pulsars.^[ref]

One quarter each went to Raymond Davis Jr. and Masatoshi Koshiba for pioneering astrophysics through detection of cosmic neutrinos. One half went to Riccardo Giacconi for pioneering astrophysics leading to the discovery of cosmic X-ray sources.^[ref]

William Alfred Fowler studied the nuclear reactions responsible for producing chemical elements in the universe, combining experiments with calculations in nuclear physics and astrophysics. His 1983 Nobel lecture explains this research as a search for the origin of the chemical elements. Measuring the reaction rates of nuclear reactions makes a laboratory result useful for models of stellar evolution and nucleosynthesis; a proposed reaction network needs both viable pathways and rates under the relevant stellar conditions.^[ref]