spiral galaxy

spiral galaxy
Name	Spiral galaxy
Caption	Artist's impression of a grand-design spiral
Type	Disk galaxy
Constellation	Various
Redshift	Various
Dist ly	Various
Mass	10^9–10^12 M☉
Radius	5–50 kpc
Stars	10^8–10^12

spiral galaxy

Spiral galaxies are rotating disk-shaped stellar systems characterized by prominent arms, a central bulge, and a surrounding dark matter halo. They appear across the local universe in environments ranging from the Local Group to the Virgo Cluster and are exemplified by systems such as Milky Way, Andromeda Galaxy, and Pinwheel Galaxy. Spiral galaxies play central roles in studies by observatories and missions like Hubble Space Telescope, Sloan Digital Sky Survey, and ALMA.

Overview

Spiral galaxies are major constituents of the Hubble sequence alongside elliptical galaxy and lenticular galaxy, occupying diverse environments in structures like the Local Supercluster and the Coma Cluster. Surveys such as 2MASS and GALEX quantify their stellar populations and star-formation rates, while theoretical frameworks from groups at Max Planck Institute for Astronomy and Harvard–Smithsonian Center for Astrophysics model their dynamics. Iconic nearby examples include Milky Way and Andromeda Galaxy; more distant spirals are mapped in campaigns like COSMOS and CANDELS.

Structure and Components

The canonical components are the stellar disk, spiral arms, central bulge, bar (when present), interstellar medium, and an extended dark matter halo traced by rotation curves measured by teams using Very Large Array and Keck Observatory. The bulge in systems such as M31 (Andromeda Galaxy) hosts older populations studied with instruments like James Webb Space Telescope, while disks contain mixed-age populations probed by Gaia and Chandra X-ray Observatory. Gas phases include cold molecular clouds observable with ALMA, warm neutral gas mapped by Arecibo Observatory surveys, and ionized gas revealed by Sloan Digital Sky Survey spectroscopy. Supermassive black holes in centers, exemplified by measurements of Sagittarius A* and nuclei in M81, influence nuclear activity classified by catalogs from Sloan Digital Sky Survey and monitored by facilities such as Very Large Telescope.

Formation and Evolution

Formation scenarios invoke hierarchical assembly in the context of Lambda-CDM cosmology studied by simulation suites like Illustris and EAGLE. Disk formation follows gas cooling in halos described in work from Kip Thorne-era theory and later by groups at Cambridge University, with angular momentum acquisition via tidal torques from structures identified in Large-scale structure of the cosmos. Secular processes driven by bars and spiral density waves, investigated by researchers at Max Planck Institute for Astrophysics and Carnegie Institution for Science, re-distribute mass and angular momentum, while major mergers catalogued in surveys such as GAMA can transform spirals into elliptical galaxy or produce peculiar systems like Antennae Galaxies. Chemical evolution traced by projects like APOGEE records enrichment from generations of stars and contributions from events such as Type Ia supernova and core-collapse supernova.

Classification and Morphology

Classification schemes include the original Hubble tuning fork refined by de Vaucouleurs' system used at institutes like NASA and European Southern Observatory. Subclasses—grand-design, flocculent, and multi-armed—are exemplified by M51 (grand-design) and NGC 2841 (flocculent). Bars produce SB types as in NGC 1300, while unbarred SA types include M33. Morphological metrics from projects like Galaxy Zoo and instruments such as Hubble Space Telescope enable statistical distinctions between early-type and late-type spirals across catalogs like HyperLeda.

Star Formation and Dynamics

Star formation in spiral arms is regulated by processes such as spiral density waves and feedback from massive stars and supernova remnants; observational programs like PHANGS and HERACLES quantify cloud-scale star formation with facilities including ALMA and HST. Rotation curves measured by teams using Keck Observatory and Very Large Array reveal flat profiles attributed to dark matter halos studied in works at University of California, Berkeley and Princeton University. Pattern speeds of bars and spiral modes are constrained with methods developed at University of Chicago and applied to galaxies like NGC 1365. Stellar populations are dated via spectroscopy from Sloan Digital Sky Survey and resolved-star photometry by Hubble Space Telescope in nearby systems such as NGC 300.

Interactions and Environmental Effects

Environment shapes spiral evolution: tidal interactions with companions like Small Magellanic Cloud and Large Magellanic Cloud influence Milky Way morphology, while ram-pressure stripping in clusters such as Virgo Cluster and Coma Cluster can remove gas as observed in NGC 4522. Galaxy mergers cataloged by CANDELS produce morphological transformation and trigger starbursts exemplified by Mice Galaxies and Antennae Galaxies. Satellite accretion events revealed by surveys such as SDSS and analyses by institutions including Max Planck Institute for Astrophysics leave stellar streams and thickened disks as seen around Andromeda Galaxy and Milky Way. Active nuclei in cluster and field environments, cataloged by Chandra X-ray Observatory and Very Large Telescope, further modulate star formation through feedback processes.

Category:Galaxies