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The process by which stars produce heavier elements from hydrogen and helium through nuclear fusion reactions, occurring in the cores of stars.

Chemical reactions involving the transfer of electrons between two species which can take place in various interstellar environments, such as on the surfaces of dust grains.

The process of creating new atomic nuclei from pre-existing nucleons (protons and neutrons) during the explosive death of a star, resulting in the production of many heavy elements.

A form of naturally occurring nuclear fission and nucleosynthesis where cosmic rays impact atoms, causing them to break apart into lighter elements, mainly occurring in interstellar space.

A chemical process that occurs when two atoms or molecules join together as a result of emitting a photon, this commonly occurs in the cold interstellar medium.

The breaking apart of chemical bonds due to the absorption of a photon, seen in regions with strong ultraviolet radiation such as the proximity of massive stars.

The process opposite to adsorption where molecules are released from the surfaces of dust grains into the gas phase, often triggered by thermal, chemical, or photonic stimuli.

The process where a molecular ion recombines with an electron, leading to the ejection of atoms from the molecule, prevalent in regions like planetary nebulae.

The gradual accumulation of matter, such as gas and dust, into larger bodies like stars, planets, and asteroids, driven by gravitational attraction.

The process of ionizing an atom or molecule by absorbing a photon, typically occurring in nebulae where high-energy light from nearby stars is present.

The process by which gas clouds lose heat by emitting radiation, allowing the clouds to cool and eventually collapse to form new stars and planets.

The process where a comet releases gas and dust as it is heated by the Sun, leading to the creation of a coma and tail, and contributing to the delivery of organic compounds to other celestial bodies.

The process by which interstellar clouds collapse under their own gravity to form stars and planetary systems, a fundamental process in the creation of stellar bodies.

A process occurring during the formation of a planet where denser materials sink towards the center while less dense materials rise, creating the layered structure of the planet.

The process of two hydrogen atoms combining to form a hydrogen molecule ($H_2$), predominantly taking place on the surfaces of interstellar dust grains.

The process by which a dense region within a molecular cloud collapses under its own gravity to eventually form a star, often leading to the formation of protostars.

The process by which atoms, ions, or molecules adhere to the surfaces of dust grains in space, playing a vital role in molecular cloud chemistry.

Chemical reactions between ions and neutral molecules, a fundamental process in the chemistry of the interstellar medium, resulting in the formation of complex organic molecules.

A process connected to the absorption of specific wavelengths of light by interstellar dust or gas, causing opaque bands in the spectra of stars, indicative of complex molecules in space.