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| Galactic plane | |
|---|---|
| Name | Galactic plane |
| Caption | Edge-on view of a spiral galaxy illustrating a thin stellar disk and midplane dust lane |
| Type | Astronomical plane |
| Galaxy | Milky Way |
| Coordinates | Galactic coordinates |
Galactic plane is the flattened, median plane defining the disk-like distribution of stars, gas, dust, and compact objects in a disk galaxy. It serves as a reference for Milky Way coordinate systems, informs models used by Hubble Space Telescope, Gaia, Spitzer Space Telescope, Sloan Digital Sky Survey, and structures studied by missions such as Chandra X-ray Observatory, James Webb Space Telescope, and WISE. Studies of the plane employ instruments from observatories like Very Large Array, ALMA, Keck Observatory, and Arecibo Observatory (historical).
The plane is defined observationally by the median distribution of luminous tracers such as OB stars cataloged by Hipparcos, Gaia sources, masers from Very Long Baseline Array, and pulsars compiled by the ATNF Pulsar Catalogue. Orientation references include the International Astronomical Union-established galactic coordinate system tied to the position of the Galactic Center and the radio source Sagittarius A*. Historically, determinations used catalogs from Henry Draper Catalogue, Messier catalog, and surveys like Two Micron All-Sky Survey and IRAS to refine tilt and warp relative to surveys by William Herschel and analyses by Jan Oort and Bertil Lindblad.
Within disk galaxies, the plane coincides with the thin disk and the midplane dust lane seen in images of systems such as Andromeda Galaxy, NGC 4565, and NGC 891. Components concentrated near the plane include populations from the Hipparcos and Gaia catalogs, open clusters cataloged in New General Catalogue, molecular clouds mapped by CO surveys and instruments like FCRAO, and H II regions identified in surveys by Sharpless, Reynolds and radio recombination line studies by GBT. The plane hosts young OB associations, star-forming regions like Orion Nebula and Carina Nebula, giant molecular complexes such as the Perseus Arm, Scutum–Centaurus Arm, and the Sagittarius Arm. Embedded within are compact remnants connected to Cassiopeia A, Crab Nebula, and X-ray binaries cataloged by RXTE. Metallicity gradients measured by teams associated with European Southern Observatory and Keck Observatory show radial variation across the plane. Vertical structure includes the thin disk, thick disk described in work by Gilmore and Reid, and flaring/warp features analogous to those modeled in Lambda-CDM cosmology simulations by groups at Princeton University and Max Planck Institute for Astrophysics.
The plane is prominent in optical surveys like Palomar Observatory Sky Survey but heavily obscured by dust seen in Infrared Astronomical Satellite and Spitzer Space Telescope maps; radio surveys by Parkes Observatory and Arecibo Observatory (historical) penetrate extinction. Emission-line tracers include 21 cm neutral hydrogen mapped by HI4PI and Leiden/Argentine/Bonn Survey, molecular CO mapped by FCRAO and Nobeyama Radio Observatory, and far-infrared emission from Herschel Space Observatory and Planck (spacecraft). High-energy population studies leverage Fermi Gamma-ray Space Telescope, INTEGRAL, and Chandra X-ray Observatory catalogs to probe cosmic-ray interactions and supernova remnants like Tycho's Supernova Remnant. Polarimetric surveys by SOFIA and Planck trace magnetic field geometry across the plane.
Dynamical influence arises through mass distribution in the plane driving rotation curves measured by Vera C. Rubin Observatory-era analogs, HI surveys, and stellar kinematics from Gaia. Nonaxisymmetric structures such as bars (modeled after the Milky Way bar) and spiral density waves studied in contexts like the Lin–Shu hypothesis influence streaming motions and resonances cataloged in research by Toomre, Athanassoula, and Sellwood. Secular processes including radial migration described by Sellwood and Binney alter stellar populations along the plane; interactions with satellites like Sagittarius Dwarf Spheroidal Galaxy and mergers recorded in observations of Gaia-Enceladus imprint phase-space substructure. Torque exchange with dark matter halos investigated by groups at Harvard–Smithsonian Center for Astrophysics and University of Cambridge shapes warp evolution.
The plane concentrates cold gas reservoirs fueling star formation rates benchmarked against galaxies in surveys like SINGS and THINGS. Giant molecular clouds studied with ALMA, IRAM, and JCMT collapse to form clusters comparable to those in 30 Doradus and Westerlund 1. Feedback from massive stars cataloged by Hubble Space Telescope and supernovae observed by Chandra X-ray Observatory and Fermi drives turbulence, regulates the Kennicutt–Schmidt relation popularized by Robert Kennicutt, and sculpts shells seen in surveys by Large Millimeter Telescope. Cosmic-ray propagation along the plane interacts with magnetic structures examined by LOFAR and VLA.
Mapping uses astrometry from Gaia and Hipparcos for stellar midplane definition, spectroscopic surveys like APOGEE, LAMOST, and RAVE for radial velocities and chemistry, and radio interferometry from VLBI arrays to measure parallaxes to masers in high-mass star-forming regions. Emission mapping employs 21 cm observations by GBT and Parkes Observatory, CO surveys using Nobeyama and IRAM, and infrared surveys from WISE, Spitzer Space Telescope, and Herschel Space Observatory. Machine-learning analyses developed at institutions such as Stanford University and Massachusetts Institute of Technology combine datasets from missions like Sloan Digital Sky Survey and Pan-STARRS to produce 3D dust maps and extinction-corrected stellar density reconstructions.
Understanding the plane informs comparative studies of disk galaxies like M81, M33, and NGC 2403 and guides interpretation of edge-on systems observed by Hubble Space Telescope and James Webb Space Telescope. Extinction and foreground contamination along the plane affect extragalactic surveys including Dark Energy Survey and Euclid (spacecraft), biasing detection of high-redshift objects cataloged by Keck Observatory and Very Large Telescope. Models of baryonic distribution in the plane constrain mass decomposition used in rotation curve studies pioneered by Vera Rubin and dark matter halo analyses conducted at Los Alamos National Laboratory and CERN-affiliated groups. Mapping of the plane is essential for planning transient follow-up by facilities like LIGO, Zwicky Transient Facility, and Neil Gehrels Swift Observatory.