Physical world and mathematics

Gaia Data Release 3

Gaia Data Release 3, or Gaia DR3, is a 2022 catalog from the European Space Agency's Gaia mission covering about 1.8 billion stars and other objects.

Gaia Sausage

The Gaia Sausage, also called Gaia-Enceladus, is a structure of radial-orbit stars in the Milky Way's inner halo from a dwarf galaxy merger about 10 billion years ago.

Gaia-ESO Survey

The Gaia-ESO Survey was a public spectroscopic survey by the European Southern Observatory that obtained spectra of more than 100,000 stars across all major components of the Milky Way.

Gail Kineke

Gail C. Kineke is an American coastal oceanographer at Boston College who studies fine-sediment transport and fluid muds, and received a Presidential Early Career Award in 1996.

Gain saturation is the reduction of a laser medium's optical gain as signal intensity rises, when stimulated emission depletes the pumping-built population inversion, clamping laser gain at threshold.

Gaining stream

A gaining stream is a stream reach that receives groundwater, which discharges through the streambed where the water table stands higher than the stream's water surface, sustaining baseflow.

Galactic anticenter

The galactic anticenter is the direction on the sky exactly opposite the Milky Way's center, in Gemini, used by astronomers to study the Galaxy's outer disk.

Galactic bar

A galactic bar is an elongated concentration of stars, gas, and dust cutting across the center of a disc galaxy, found in nearly two-thirds of nearby disc galaxies.

Galactic bulge

A galactic bulge is the dense central concentration of stars, mostly old, that swells out of the disk of a spiral galaxy. The Milky Way's bulge is a bar with an X-shaped structure.

Galactic Center

The Galactic Center is the rotational and gravitational center of the Milky Way, about 26,000 light-years from Earth, marked by the supermassive black hole Sagittarius A.

Galactic Center GeV excess

The Galactic Center GeV excess, also called GCE, is an unexplained gamma-ray glow at the Milky Way's center, first seen in 2009 and debated as dark matter or pulsars.

Galactic Center radio filaments

Galactic Center radio filaments, also called non-thermal filaments, are narrow magnetic structures up to 100 light-years long near the Milky Way's center, first identified in 1984.

Galactic Center X-ray chimneys

The Galactic Center X-ray chimneys are two plumes of hot plasma, hundreds of parsecs long, extending from the center of the Milky Way toward the Fermi bubbles, first reported in 2019.

Galactic chimney

A galactic chimney is a collimated channel of hot, overpressured gas created when a supernova-driven superbubble bursts out of a galaxy's disk into its halo, carrying mass and energy upward.

Galactic disk

The galactic disk is the flattened, rotating component of a disk galaxy, made of stars, gas, and dust and distinct from the central bulge and halo.

Galactic dynamics

Galactic dynamics is the study of motions within the Milky Way, where Gaia data since 2018 revealed a phase spiral showing the disk was perturbed hundreds of millions of years ago.

Galactic fountain

A galactic fountain is the circulation of interstellar gas in a spiral galaxy in which supernova-heated gas rises into the halo, cools, and falls back.

Galactic halo

A galactic halo, or galaxy halo, is the roughly spherical component surrounding a galaxy's visible disk and bulge, dominated by dark matter and containing old, metal-poor stars.

Galactic plane

The galactic plane is the plane containing most of the disk of the Milky Way Galaxy, appearing in the sky as the luminous band of the Milky Way.

Galactic tide

A galactic tide is the differential gravitational field of a galaxy, which torques distant Oort cloud comets and sends long-period comets into the inner Solar System.

Galactic warp

A galactic warp is a bending of a spiral galaxy's disk out of its own midplane, and the Milky Way's outer disk shows such a warp.

Galactose

Galactose is a monosaccharide sugar and the C-4 epimer of glucose, found mainly in lactose in milk and metabolized by the Leloir pathway, whose enzyme deficiencies cause galactosemia.

Galacturonic acid

Galacturonic acid (GalA) is a sugar acid derived from galactose by oxidation of its terminal alcohol, best known as the principal building block of pectin in plant cell walls.

Galanin

Galanin is a 29-amino-acid neuropeptide (30 in humans), isolated from porcine intestine at the Karolinska Institute in 1983, that modulates neurotransmission and endocrine secretion through the receptors GalR1, GalR2, and GalR3.

Galaxy

A galaxy is a gravitationally bound system of stars, gas, dust, and dark matter, ranging from dwarfs with a few thousand stars to giants with trillions.

Galaxy And Mass Assembly survey

The Galaxy And Mass Assembly (GAMA) survey is a spectroscopic survey of about 290,000 nearby galaxies, made with the AAOmega spectrograph on the Anglo-Australian Telescope from 2008 to 2014.

Galaxy cluster

A galaxy cluster is a gravitationally bound system of galaxies, hot X-ray-emitting plasma, and dark matter, about 80% dark matter, and the site of the most energetic events since the Big Bang.

Galaxy color–magnitude diagram

The galaxy color–magnitude diagram is a scatter plot of galaxies by color and absolute magnitude, separating them into a red sequence, a blue cloud, and a green valley.

Galaxy filament

A galaxy filament, also called a cosmic filament, is a thread-like concentration of dark matter, gas, and galaxies, a few to hundreds of megaparsecs long, connecting clusters and bounding voids.