Cosmology and observation

Primordial gravitational waves

Primordial gravitational waves are ripples in spacetime generated during inflation, leaving a B-mode imprint in the cosmic microwave background polarization that experiments search for today.

Primordial magnetic fields

Primordial magnetic fields are magnetic fields generated in the early universe, during inflation or cosmological phase transitions. None has been directly detected; they are constrained through the cosmic microwave background, nucleosynthesis, and gamma-ray observations.

Primordial power spectrum

The primordial power spectrum describes the amplitude of density and curvature fluctuations in the very early Universe as a function of scale, seeding CMB anisotropies and galaxy distribution.

Proxima Centauri b

Proxima Centauri b, also known as Proxima b, is an exoplanet orbiting Proxima Centauri, the Sun's closest neighbor, detected in 2016 with a minimum mass of about 1.2 Earth masses.

Proxima Centauri d

Proxima Centauri d (also written Proxima d) is a terrestrial exoplanet orbiting Proxima Centauri, the closest star to the Sun, with a minimum mass of about 0.26 Earth masses.

QSO B0420-0127

QSO B0420-0127, also known as PKS 0420-014 and 4FGL J0423.3-0120, is a blazar in Orion at redshift 0.916, a flat-spectrum radio quasar whose superluminal jet has been monitored across the spectrum since 1969.

QSO B1730-130

QSO B1730-130, also known as NRAO 530 or PKS 1730-130, is a blazar at redshift 0.90 and the most distant object imaged by the Event Horizon Telescope.

QSO J0529−4351

QSO J0529−4351 (SMSS J052915.80−435152.0) is a quasar in the constellation Pictor identified in 2024 as the most luminous quasar known, powered by a 17-billion-solar-mass black hole.

QSO J0738+1742

QSO J0738+1742, also known as PKS 0735+178, is a BL Lacertae object, a blazar whose relativistic jet points nearly at Earth; in 2021 it became a candidate source of an IceCube neutrino.

QSO J1512-0906

QSO J1512-0906, better known in the literature as PKS 1510-089, is a flat-spectrum radio quasar at redshift 0.361 with a jet pointed almost directly at Earth.

Quantum Circuits

S. Harvey Moseley is an American astronomer and instrumentation physicist elected to the National Academy of Sciences in 2023, known for NASA's COBE, cryogenic X-ray detectors, and JWST microshutters.

Quasar clustering

Quasar clustering is the statistical excess of quasar pairs at given separations, measured to show how these active supermassive black holes trace the large-scale structure of the universe.

Quasar Hubble diagram

The quasar Hubble diagram is a plot of distance against redshift for quasars, using their UV and X-ray luminosity relation to test cosmology at redshifts beyond Type Ia supernovae.

Quasar luminosity function

The quasar luminosity function is the comoving number density of quasars per unit luminosity, whose evolution with redshift traces the history of accretion onto supermassive black holes.

Quasar quartet

The quasar quartet is the first known system of four quasars in close proximity, discovered in 2015 with the Keck I Telescope in Hawaii and announced in Science.

QUBIC

QUBIC, the Q&U Bolometric Interferometer for Cosmology, is a ground-based experiment measuring CMB polarization to detect B-modes from inflationary gravitational waves, observing from about 4,900 meters in Salta, Argentina.

QUIJOTE CMB experiment

QUIJOTE (Q-U-I JOint TEnerife) is a ground-based polarimeter at the Teide Observatory in Tenerife, Spain, measuring cosmic microwave background polarization at 10–42 GHz since 2012.

Quipu (cosmic structure)

Quipu, named for the Incan knotted cords, is a filamentary superstructure of galaxy clusters identified in 2025 as the largest found in its survey, about 1.3 billion light-years long with a mass of 200 quadrillion Suns.

Radial acceleration relation

The radial acceleration relation (RAR) is an empirical correlation in galaxies between observed gravitational acceleration and that predicted from visible matter, established by McGaugh, Lelli, and Schombert in 2016.

Sep 29, 2026

Radial velocity method

The radial velocity method detects exoplanets by measuring periodic Doppler shifts in a star's spectral lines as the star moves under an orbiting planet's gravity.

Radiation-dominated era

The radiation-dominated era is the period of cosmic history, from the Big Bang until roughly 50,000 years after it, when radiation's energy density exceeded matter's and controlled the universe's expansion, ending at matter-radiation equality.

Radio halo

A radio halo is a diffuse region of synchrotron radio emission at the center of a galaxy cluster, produced by relativistic electrons in magnetic fields.

Sep 29, 2026

Radio interferometry

Radio interferometry is a radio astronomy technique that combines signals from separated antennas to synthesize high-resolution sky images, developed by Martin Ryle, who won the 1974 Nobel Prize in physics.

Radio mode feedback

Radio mode feedback is a mode of active galactic nucleus feedback in which the mechanical energy of radio jets heats gas in massive elliptical galaxies and suppresses cooling and star formation.

Radio telescope

A radio telescope is an antenna and receiving system that collects and measures radio waves from celestial bodies; most are parabolic dishes, and the largest are interferometer arrays.

Radio transient

A radio transient is an astronomical source that appears at radio wavelengths where no quiescent counterpart is detected, arising from flaring stars, neutron stars, supernovae, and active galactic nuclei.

Radio-loud quasar

A radio-loud quasar is a quasar whose radio emission, powered by relativistic jets from its central black hole, is strong compared with its optical emission.

Radio-loudness parameter

The radio-loudness parameter R is the ratio of a quasar's radio to optical flux, classically 5 GHz to 4400 Å, dividing quasars into radio-loud and radio-quiet classes.

Radius valley

The radius valley, also known as the radius gap or Fulton gap, is a scarcity of close-in exoplanets between 1.5 and 2.0 Earth radii, first resolved by the California-Kepler Survey in 2017.