{"dataset":{"slug":"galactic-astronomy","title":"Galactic Astronomy & the Milky Way","description":"The anatomy and life of our Galaxy — the structural components (thin & thick discs, bulge, bar, stellar halo, spiral arms, warp, Galactic Centre, central molecular zone, corona) and the dynamical & archaeological phenomena (rotation & dark matter, stellar streams, radial migration, galactic archaeology, magnetic field, satellite accretion, the Andromeda collision).","version":"1.0.0","lastGenerated":"2026-06-29","license":"CC BY-SA 4.0","entityCount":20,"sources":["nasa","eso"]},"entities":[{"id":"galactic_dynamics:galactic-archaeology","name":"Galactic Archaeology","type":"galactic_dynamics","domain":"science","description":"The reconstruction of how the Milky Way formed by reading the ages, chemistry, and motions of its stars, which preserve the imprint of their birth. Gaia's precise positions and velocities for over a billion stars have turned this into a precision science, revealing ancient mergers frozen into the halo.","entryPath":"/galactic-astronomy/galactic-archaeology"},{"id":"galactic_dynamics:galactic-rotation","name":"Galactic Rotation","type":"galactic_dynamics","domain":"science","description":"The Milky Way's disc does not turn as a solid body: inner and outer stars complete their orbits at different rates. Yet the orbital speed stays surprisingly flat far from the centre instead of falling off, one of the clearest signs that the visible Galaxy is embedded in a massive halo of unseen dark matter.","entryPath":"/galactic-astronomy/galactic-rotation"},{"id":"galactic_dynamics:stellar-migration","name":"Radial Migration","type":"galactic_dynamics","domain":"science","description":"Stars do not stay at the galactocentric radius where they were born. Resonances with the spiral arms and the bar can shuffle a star inward or outward across the disc without heating its orbit, mixing the disc's chemistry over billions of years and complicating any attempt to read history from composition alone.","entryPath":"/galactic-astronomy/stellar-migration"},{"id":"galactic_dynamics:satellite-galaxies-and-accretion","name":"Satellite Galaxies & Accretion","type":"galactic_dynamics","domain":"science","description":"The Milky Way is orbited by dozens of smaller galaxies, the brightest being the Large and Small Magellanic Clouds. In the hierarchical picture of galaxy formation, big galaxies grow by swallowing small ones, and the Milky Way is still feeding — its halo and streams are the debris of satellites consumed long ago.","entryPath":"/galactic-astronomy/satellite-galaxies-and-accretion"},{"id":"galactic_dynamics:stellar-streams","name":"Stellar Streams","type":"galactic_dynamics","domain":"science","description":"Ribbons of stars strung out across the halo, torn from dwarf galaxies and globular clusters as the Milky Way's tides pull them apart. The great Sagittarius stream wraps entirely around the Galaxy; mapped in their dozens by Gaia, these streams trace the shape of the dark-matter halo and record the Galaxy's past meals.","entryPath":"/galactic-astronomy/stellar-streams"},{"id":"galactic_structure:central-molecular-zone","name":"The Central Molecular Zone","type":"galactic_structure","domain":"science","description":"The reservoir of dense molecular gas within a few hundred parsecs of the Galactic Centre — a fraction of the Galaxy's volume that holds a large share of its molecular material. Turbulent, magnetised, and forming stars under extreme conditions, it is a nearby laboratory for the hearts of other galaxies.","entryPath":"/galactic-astronomy/central-molecular-zone"},{"id":"galactic_structure:galactic-bar","name":"The Galactic Bar","type":"galactic_structure","domain":"science","description":"An elongated bar of stars spanning the central few kiloparsecs, which makes the Milky Way a barred spiral galaxy. The bar funnels gas inward, drives the boxy bulge, and sets up resonances that shape the orbits of disc stars far from the centre.","entryPath":"/galactic-astronomy/galactic-bar"},{"id":"galactic_structure:galactic-bulge","name":"The Galactic Bulge","type":"galactic_structure","domain":"science","description":"The dense, roughly spheroidal concentration of mostly old stars at the heart of the Milky Way. Boxy and peanut-shaped when seen edge-on, the bulge is intimately tied to the central bar and holds clues to how the inner Galaxy assembled.","entryPath":"/galactic-astronomy/galactic-bulge"},{"id":"galactic_structure:galactic-center","name":"The Galactic Centre","type":"galactic_structure","domain":"science","description":"The crowded, dust-shrouded core of the Milky Way, about 26,000 light-years away, home to a dense star cluster and the four-million-solar-mass black hole Sagittarius A*. Hidden at optical wavelengths, it is studied in radio, infrared, and X-rays, and its stars' orbits weigh the central black hole directly.","entryPath":"/galactic-astronomy/galactic-center"},{"id":"galactic_structure:galactic-corona","name":"The Galactic Corona","type":"galactic_structure","domain":"science","description":"An enormous halo of tenuous, million-degree gas that surrounds the Milky Way, detectable in X-rays and in absorption against distant sources. This hot corona is a reservoir of baryons and the medium through which fresh gas accretes onto the Galaxy and enriched gas is expelled.","entryPath":"/galactic-astronomy/galactic-corona"},{"id":"galactic_dynamics:galactic-fountain","name":"The Galactic Fountain","type":"galactic_dynamics","domain":"science","description":"Star formation and supernovae blow hot gas out of the disc, which cools, condenses, and rains back down as clouds — a continual circulation between the disc and the halo. This galactic fountain recycles and mixes gas, and helps deliver the fresh material that keeps the Milky Way forming stars.","entryPath":"/galactic-astronomy/galactic-fountain"},{"id":"galactic_dynamics:the-galactic-habitable-zone","name":"The Galactic Habitable Zone","type":"galactic_dynamics","domain":"science","description":"A proposed — and much-debated — region of the Galaxy thought to be most favourable to complex life: far enough from the crowded, radiation-soaked centre yet metal-rich enough to build planets. Whether such a zone is truly well-defined remains an open question, and it is offered as a hypothesis rather than an established boundary.","entryPath":"/galactic-astronomy/the-galactic-habitable-zone"},{"id":"galactic_dynamics:galactic-magnetic-field","name":"The Galactic Magnetic Field","type":"galactic_dynamics","domain":"science","description":"A large-scale magnetic field of a few microgauss threads the Milky Way, ordered along the spiral arms and tangled on smaller scales. Weak though it is, it guides cosmic rays, shapes the interstellar medium, and helps regulate star formation; it is traced through synchrotron radiation, Faraday rotation, and polarised starlight and dust.","entryPath":"/galactic-astronomy/galactic-magnetic-field"},{"id":"galactic_structure:galactic-warp","name":"The Galactic Warp","type":"galactic_structure","domain":"science","description":"The outer disc of the Milky Way is not flat but bent, curving up on one side and down on the other like a vinyl record left in the sun. This warp, traced by gas and by young stars, is likely stirred by the gravitational tug of the Magellanic Clouds and the dark-matter halo.","entryPath":"/galactic-astronomy/galactic-warp"},{"id":"galactic_dynamics:the-milky-way-andromeda-collision","name":"The Milky Way–Andromeda Collision","type":"galactic_dynamics","domain":"science","description":"The Milky Way and the Andromeda Galaxy are approaching each other and are predicted to merge into a single elliptical galaxy in roughly four to five billion years, though the exact timing and geometry remain uncertain. Stars will almost never collide, but both discs will be transformed as the two giants of the Local Group become one.","entryPath":"/galactic-astronomy/the-milky-way-andromeda-collision"},{"id":"galactic_structure:the-solar-neighbourhood","name":"The Solar Neighbourhood","type":"galactic_structure","domain":"science","description":"The Sun's local patch of the Galaxy — the stars, gas, and structure within a few hundred light-years. It includes the Local Bubble, a cavity of hot, thin gas blown by ancient supernovae, and it is the vantage point from which we map the entire Milky Way, orbiting the Galactic Centre once every roughly 230 million years.","entryPath":"/galactic-astronomy/the-solar-neighbourhood"},{"id":"galactic_structure:spiral-arms","name":"The Spiral Arms","type":"galactic_structure","domain":"science","description":"The bright lanes that wind through the disc, marked out by gas, dust, and freshly-formed luminous stars. The arms are thought to be density waves — regions where orbits crowd together and trigger star formation — rather than fixed structures, so stars drift in and out of them over time.","entryPath":"/galactic-astronomy/spiral-arms"},{"id":"galactic_structure:stellar-halo","name":"The Stellar Halo","type":"galactic_structure","domain":"science","description":"A vast, sparse, roughly spherical cloud of the Galaxy's oldest and most metal-poor stars, together with its globular clusters, reaching far beyond the disc. Built largely from the shredded remains of smaller galaxies, the stellar halo is the Milky Way's deep archaeological archive.","entryPath":"/galactic-astronomy/stellar-halo"},{"id":"galactic_structure:galactic-thick-disk","name":"The Thick Disk","type":"galactic_structure","domain":"science","description":"A more extended, puffed-up disc of older, more metal-poor stars that envelops the thin disk. Its stars move on hotter orbits and formed early in the Galaxy's history, making the thick disk a fossil record of a more turbulent youth — perhaps heated by an ancient merger.","entryPath":"/galactic-astronomy/galactic-thick-disk"},{"id":"galactic_structure:galactic-thin-disk","name":"The Thin Disk","type":"galactic_structure","domain":"science","description":"The flattened, rotating layer that holds most of the Milky Way's stars, gas, and dust, and where stars are still being born today. Only a few hundred parsecs thick but tens of thousands across, it contains the spiral arms and the young, metal-rich stars of the Galactic disc — the Sun among them.","entryPath":"/galactic-astronomy/galactic-thin-disk"}]}