Astrophysics

The hydrogen anion is a negative ion of hydrogen, H−.

This is a list of black holes (and stars considered probable candidates) organized by size (including black holes of undetermined mass); some items in this list are galaxies or star clusters that are believed to be organized around a black hole.

A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence.

A Cepheid variable (/ˈsɛfiːɪd/ or /ˈsiːfiːɪd/) is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.

The cosmic microwave background (CMB) is the thermal radiation left over from the time of recombination in Big Bang cosmology.

Cosmochemistry (from Greek κόσμος kósmos, "universe" and χημεία khemeía) or chemical cosmology is the study of the chemical composition of matter in the universe and the processes that led to those compositions.

Cosmology (from the Greek κόσμος, kosmos "world" and -λογία, -logia "study of"), is the study of the origin, evolution, and eventual fate of the universe.

Differential rotation is seen when different parts of a rotating object move with different angular velocities (rates of rotation) at different latitudes and/or depths of the body and/or in time.

In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer.

Gamma-ray bursts (GRBs) are extremely energetic explosions that have been observed in distant galaxies.

A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer, that is capable of bending the light from the source as the light travels towards the observer.

In astronomy, the interstellar medium (ISM) is the matter that exists in the space between the star systems in a galaxy.

Photodissociation, photolysis, or photodecomposition is a chemical reaction in which a chemical compound is broken down by photons.

Plasma (from Greek πλάσμα, "anything formed") is one of the four fundamental states of matter, the others being solid, liquid, and gas.

In physics, redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum.

The solar wind is a stream of charged particles released from the upper atmosphere of the Sun.

In astronomy, stellar classification is the classification of stars based on their spectral characteristics.

Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of mass.

The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1926.

Kvant-1 (Russian: Квант-1; English: Quantum-I/1) (37KE) was the first module to be attached in 1987 to the Mir Core Module, which formed the core of the Soviet space station Mir.

Neutronium (sometimes shortened to neutrium) is a proposed name for a substance composed purely of neutrons.

In physics, optical depth or optical thickness, is the natural logarithm of the ratio of incident to transmitted radiant power through a material, and spectral optical depth or spectral optical thickness is the natural logarithm of the ratio of incident to transmitted spectral radiant power through a material.

The proton–proton chain reaction is one of the two (known) sets of fusion reactions by which stars convert hydrogen to helium.

Stellar rotation is the angular motion of a star about its axis.

An accretion disk is a structure (often a circumstellar disk) formed by diffused material in orbital motion around a massive central body.

An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much higher than normal luminosity over at least some portion – and possibly all – of the electromagnetic spectrum.

Compton scattering, discovered by Arthur Holly Compton, is the inelastic scattering of a photon by a charged particle, usually an electron.

A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite.

The Kelvin–Helmholtz mechanism is an astronomical process that occurs when the surface of a star or a planet cools.

A magnetosphere is the region of space surrounding an astronomical object in which charged particles are controlled by that object's magnetic field.

Mira variables /ˈmaɪrə/ ("Mira", Latin, adj. - feminine form of adjective "wonderful"), named for the prototype star Mira, are a class of pulsating variable stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.

In astrophysics and physical cosmology, Olbers' paradox, named after the German astronomer Heinrich Wilhelm Olbers (1758–1840) and also called the "dark night sky paradox", is the argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe.

Wolf–Rayet stars, often abbreviated as WR stars, are a heterogeneous set of stars with unusual spectra showing prominent broad emission lines of highly ionised helium and nitrogen or carbon.

Tired light is a class of hypothetical redshift mechanisms that was proposed as an alternative explanation for the redshift-distance relationship.

Tensor–vector–scalar gravity (TeVeS), developed by Jacob Bekenstein in 2004, is a relativistic generalization of Mordehai Milgrom's Modified Newtonian dynamics (MOND) paradigm.

The Innermost stable circular orbit (often called the ISCO) is the smallest orbit in which a test particle can stably orbit a massive object in general relativity.

In astrophysics, a polytrope refers to a solution of the Lane–Emden equation in which the pressure depends upon the density in the form where P is pressure, ρ is density and K is a constant of proportionality.

Black-body radiation is the type of electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body (an opaque and non-reflective body), assumed for the sake of calculations and theory to be held at constant, uniform temperature.

Physical cosmology is the study of the largest-scale structures and dynamics of the Universe and is concerned with fundamental questions about its origin, structure, evolution, and ultimate fate.

Plasma parameters define various characteristics of a plasma, an electrically conductive collection of charged particles that responds collectively to electromagnetic forces.

In astronomy and cosmology, dark fluid is an alternative theory to both dark matter and dark energy and attempts to explain both phenomena in a single framework.

In astronomical spectroscopy, the Gunn–Peterson trough is a feature of the spectra of quasars due to the presence of neutral hydrogen in the Intergalactic Medium (IGM).

The standard solar model (SSM) is a mathematical treatment of the Sun as a spherical ball of gas (in varying states of ionisation, with the hydrogen in the deep interior being a completely ionised plasma).

Cosmogenic nuclides (or cosmogenic isotopes) are rare isotopes created when a high-energy cosmic ray interacts with the nucleus of an in situ Solar System atom, causing nucleons (protons and neutrons) to be expelled from the atom (see cosmic ray spallation).

Scalar–tensor–vector gravity (STVG) is a modified theory of gravity developed by John Moffat, a researcher at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario.

Bi-scalar tensor vector gravity theory (BSTV) is an extension of the tensor–vector–scalar gravity theory (TeVeS).