{"dataset":{"slug":"deep-sky-object-classes","title":"Deep-Sky Object Classes","description":"The taxonomy of astrophysical object classes, including the deep-sky classes added by the Deep Sky Objects Encyclopedia (open & globular clusters, stellar associations, the emission/reflection/dark nebula subtypes, HII regions, Bok globules, planetary nebulae, supernova remnants) alongside the compact-object, AGN and large-scale-structure classes. Only well-established astrophysics; nothing fabricated.","version":"1.0.0","lastGenerated":"2026-06-29","license":"CC BY-SA 4.0","entityCount":32,"sources":["nasa","eso"]},"entities":[{"id":"astrophysical_object_class:active-galactic-nucleus","name":"Active Galactic Nucleus","type":"astrophysical_object_class","domain":"science","description":"A galaxy centre made unusually luminous by matter accreting onto a supermassive black hole.","entryPath":"/cosmology/active-galactic-nucleus"},{"id":"astrophysical_object_class:black-hole","name":"Black Hole","type":"astrophysical_object_class","domain":"science","description":"A region of spacetime where gravity is so strong that nothing, not even light, can escape.","entryPath":"/cosmology/black-hole"},{"id":"astrophysical_object_class:blazar","name":"Blazar","type":"astrophysical_object_class","domain":"science","description":"An active galactic nucleus whose relativistic jet points almost directly at Earth.","entryPath":"/cosmology/blazar"},{"id":"astrophysical_object_class:bok-globule","name":"Bok Globule","type":"astrophysical_object_class","domain":"science","description":"A small, dense, isolated cloud of cold gas and dust — a compact kind of dark nebula, named for Bart Bok — within which one or a few stars are collapsing into being. Bok globules are among the coldest objects in the Universe and are studied as the birthplaces of low-mass stars.","entryPath":"/deep-sky-encyclopedia/bok-globule"},{"id":"astrophysical_object_class:brown-dwarf","name":"Brown Dwarf","type":"astrophysical_object_class","domain":"science","description":"A 'failed star' too massive to be a planet but too light to sustain hydrogen fusion.","entryPath":"/cosmology/brown-dwarf"},{"id":"astrophysical_object_class:cosmic-filament","name":"Cosmic Filament","type":"astrophysical_object_class","domain":"science","description":"A thread of galaxies and dark matter stretching between clusters, forming the strands of the cosmic web.","entryPath":"/cosmology/cosmic-filament"},{"id":"astrophysical_object_class:void","name":"Cosmic Void","type":"astrophysical_object_class","domain":"science","description":"An enormous, nearly empty region of space between the filaments of the cosmic web.","entryPath":"/cosmology/void"},{"id":"astrophysical_object_class:dark-matter-halo","name":"Dark Matter Halo","type":"astrophysical_object_class","domain":"science","description":"An extended, roughly spherical cloud of dark matter within which a galaxy or cluster is embedded.","entryPath":"/cosmology/dark-matter-halo"},{"id":"astrophysical_object_class:dark-nebula","name":"Dark Nebula","type":"astrophysical_object_class","domain":"science","description":"A dense cloud of interstellar dust so opaque that it blots out the light of the stars and glowing gas behind it, appearing as a dark silhouette. Catalogued systematically by E. E. Barnard, dark nebulae are the cold, dusty reservoirs — often molecular clouds — from which new stars condense.","entryPath":"/deep-sky-encyclopedia/dark-nebula"},{"id":"astrophysical_object_class:deep-sky-object","name":"Deep-Sky Object","type":"astrophysical_object_class","domain":"science","description":"A catch-all term for any object beyond the Solar System that is neither a single star nor a planet — the star clusters, nebulae, and galaxies that fill catalogues from Messier to the NGC. Deep-sky objects are the classic targets of the amateur telescope and the workhorses of stellar and galactic astrophysics.","entryPath":"/deep-sky-encyclopedia/deep-sky-object"},{"id":"astrophysical_object_class:emission-nebula","name":"Emission Nebula","type":"astrophysical_object_class","domain":"science","description":"A cloud of interstellar gas that glows with its own light, ionised by the ultraviolet radiation of nearby hot stars so that it re-emits in characteristic lines — most famously the red of hydrogen. Emission nebulae mark regions of active star formation and include the great HII regions of the Galaxy.","entryPath":"/deep-sky-encyclopedia/emission-nebula"},{"id":"astrophysical_object_class:galaxy-cluster","name":"Galaxy Cluster","type":"astrophysical_object_class","domain":"science","description":"A gravitationally bound collection of hundreds to thousands of galaxies — the largest such structures.","entryPath":"/cosmology/galaxy-cluster"},{"id":"astrophysical_object_class:globular-cluster","name":"Globular Cluster","type":"astrophysical_object_class","domain":"science","description":"A dense, roughly spherical swarm of tens of thousands to millions of very old stars, tightly bound by gravity and orbiting in the halo of a galaxy. Globular clusters are among the oldest structures in the Universe, and their tightly packed, coeval stars make them benchmarks for stellar ages and the early history of the Galaxy.","entryPath":"/deep-sky-encyclopedia/globular-cluster"},{"id":"astrophysical_object_class:hii-region","name":"HII Region","type":"astrophysical_object_class","domain":"science","description":"A large cloud of ionised atomic hydrogen (H II) surrounding one or more hot O- and B-type stars, whose ultraviolet light strips the electrons from the surrounding gas. HII regions are the glowing signposts of massive-star formation, and their sizes and spectra are used to trace star formation across galaxies.","entryPath":"/deep-sky-encyclopedia/hii-region"},{"id":"astrophysical_object_class:intermediate-mass-black-hole","name":"Intermediate-Mass Black Hole","type":"astrophysical_object_class","domain":"science","description":"A black hole between about 100 and 100,000 solar masses — the elusive middle range.","entryPath":"/cosmology/intermediate-mass-black-hole"},{"id":"astrophysical_object_class:magnetar","name":"Magnetar","type":"astrophysical_object_class","domain":"science","description":"A neutron star with an extraordinarily powerful magnetic field, the strongest known in the Universe.","entryPath":"/cosmology/magnetar"},{"id":"astrophysical_object_class:millisecond-pulsar","name":"Millisecond Pulsar","type":"astrophysical_object_class","domain":"science","description":"An old pulsar spun up to hundreds of rotations per second by accreting matter from a companion star — 'recycled' to spin periods of only a few milliseconds. Their extraordinary rotational stability makes them the most precise clocks known and the basis of pulsar-timing arrays searching for low-frequency gravitational waves.","entryPath":"/compact-objects/millisecond-pulsar"},{"id":"astrophysical_object_class:neutron-star","name":"Neutron Star","type":"astrophysical_object_class","domain":"science","description":"The ultra-dense collapsed core of a massive star, packing more than the Sun's mass into a city-sized sphere.","entryPath":"/cosmology/neutron-star"},{"id":"astrophysical_object_class:open-cluster","name":"Open Cluster","type":"astrophysical_object_class","domain":"science","description":"A loose, irregular group of a few dozen to a few thousand stars born together from the same molecular cloud, found in the disk of the Galaxy. Their stars share an age and composition, making open clusters key laboratories for stellar evolution; because they are only weakly bound, they gradually disperse over hundreds of millions of years.","entryPath":"/deep-sky-encyclopedia/open-cluster"},{"id":"astrophysical_object_class:planetary-nebula","name":"Planetary Nebula","type":"astrophysical_object_class","domain":"science","description":"The glowing shell of gas cast off by a dying Sun-like star as it becomes a white dwarf, ionised and lit up by the hot stellar core at its centre. Despite the name — coined because their round disks resembled planets in early telescopes — planetary nebulae have nothing to do with planets; they are a brief, beautiful final phase of low- and intermediate-mass stars.","entryPath":"/deep-sky-encyclopedia/planetary-nebula"},{"id":"astrophysical_object_class:primordial-black-hole","name":"Primordial Black Hole","type":"astrophysical_object_class","domain":"science","description":"A hypothesised black hole formed from density fluctuations in the very early Universe rather than from a star.","entryPath":"/cosmology/primordial-black-hole"},{"id":"astrophysical_object_class:pulsar","name":"Pulsar","type":"astrophysical_object_class","domain":"science","description":"A rapidly rotating, magnetised neutron star observed as a source of regular pulses of radiation, usually in radio. The first was found in 1967 by Jocelyn Bell Burnell and Antony Hewish; thousands are now known, with periods from milliseconds to seconds. Pulsars are precise cosmic clocks used to test gravity and to search for gravitational waves.","entryPath":"/compact-objects/pulsar"},{"id":"astrophysical_object_class:quasar","name":"Quasar","type":"astrophysical_object_class","domain":"science","description":"The extremely luminous core of a distant galaxy powered by a feeding supermassive black hole.","entryPath":"/cosmology/quasar"},{"id":"astrophysical_object_class:reflection-nebula","name":"Reflection Nebula","type":"astrophysical_object_class","domain":"science","description":"A cloud of interstellar dust that shines not by its own emission but by scattering the light of nearby stars. Because fine dust scatters blue light most efficiently, reflection nebulae typically appear blue — as in the wisps of nebulosity draped around the Pleiades.","entryPath":"/deep-sky-encyclopedia/reflection-nebula"},{"id":"astrophysical_object_class:rotation-powered-pulsar","name":"Rotation-Powered Pulsar","type":"astrophysical_object_class","domain":"science","description":"A pulsar whose radiation is powered by the gradual loss of its rotational energy as it slowly spins down — the classic young pulsar, of which the Crab is the archetype. This is distinct from an accretion-powered X-ray pulsar, which draws its energy from infalling matter rather than from its own spin.","entryPath":"/compact-objects/rotation-powered-pulsar"},{"id":"astrophysical_object_class:stellar-association","name":"Stellar Association","type":"astrophysical_object_class","domain":"science","description":"A loose grouping of young, massive stars that formed together but are not gravitationally bound, so they drift apart over tens of millions of years. OB associations trace the sites of recent star formation along a galaxy's spiral arms and are often still embedded in the gas of their parent clouds.","entryPath":"/deep-sky-encyclopedia/stellar-association"},{"id":"astrophysical_object_class:stellar-black-hole","name":"Stellar-Mass Black Hole","type":"astrophysical_object_class","domain":"science","description":"A black hole of a few to a few dozen solar masses, formed when a massive star collapses.","entryPath":"/cosmology/stellar-black-hole"},{"id":"astrophysical_object_class:supercluster","name":"Supercluster","type":"astrophysical_object_class","domain":"science","description":"A vast grouping of galaxy clusters and groups, among the largest structures in the Universe.","entryPath":"/cosmology/supercluster"},{"id":"astrophysical_object_class:supermassive-black-hole","name":"Supermassive Black Hole","type":"astrophysical_object_class","domain":"science","description":"A black hole of millions to billions of solar masses, found at the centre of most large galaxies.","entryPath":"/cosmology/supermassive-black-hole"},{"id":"astrophysical_object_class:supernova-remnant","name":"Supernova Remnant","type":"astrophysical_object_class","domain":"science","description":"The expanding cloud of debris left behind when a star explodes as a supernova, sweeping up and shock-heating the surrounding interstellar medium. Supernova remnants seed the galaxy with heavy elements, accelerate cosmic rays, and — like the Crab — can harbour the neutron star born in the collapse.","entryPath":"/deep-sky-encyclopedia/supernova-remnant"},{"id":"astrophysical_object_class:white-dwarf","name":"White Dwarf","type":"astrophysical_object_class","domain":"science","description":"The dense, Earth-sized remnant left when a low- or medium-mass star sheds its outer layers.","entryPath":"/cosmology/white-dwarf"},{"id":"astrophysical_object_class:x-ray-pulsar","name":"X-ray Pulsar","type":"astrophysical_object_class","domain":"science","description":"A neutron star in a binary system that pulls gas from its companion; the gas is funnelled by the star's magnetic field onto its poles, where it heats up and shines in pulsed X-rays as the star rotates. X-ray pulsars are how many neutron stars are weighed, and how millisecond pulsars are recycled.","entryPath":"/compact-objects/x-ray-pulsar"}]}