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A structure formed by diffuse material in orbital motion around a central body, often a star, planet, or black hole. The material in the disk can heat up and emit radiation as it falls inwards.

A planet located outside of our solar system, orbiting a star other than the Sun. Exoplanets vary widely in size, composition, and distance from their parent stars.

A small, dense stellar remnant that is typically the size of a planet. It is what remains after a low to medium mass star has shed its outer layers and ceased nuclear burning.

A form of matter thought to account for approximately 85% of the matter in the universe. It does not emit, absorb, or reflect light, and can only be detected through its gravitational effects.

A vast cloud of dust and gas in space, often acting as a nursery for new star formation. Nebulas can be sites of complex chemical reactions and are important in the study of the interstellar medium.

A group of stars that are gravitationally bound to each other. Two main types are globular clusters, which are tight groups of hundreds of thousands of old stars, and open clusters, which are looser and contain fewer, younger stars.

An extremely bright and distant celestial object powered by a supermassive black hole at its center. Quasars are some of the most luminous objects in the universe.

A substellar object that has a mass between the heaviest gas giant planets and the lightest stars. Brown dwarfs are not massive enough to sustain hydrogen fusion in their cores.

A massive system of stars, stellar remnants, interstellar gas, dust, and dark matter, bound together by gravity. Galaxies come in various shapes and sizes, including spiral, elliptical, and irregular.

A late stage in a star's life cycle when it expands and cools after it has used up its hydrogen fuel. The outer layers are expelled, and the core becomes hotter, leading to helium fusion.

A type of neutron star with an extremely powerful magnetic field. The decay of this magnetic field powers the emission of high-energy electromagnetic radiation, such as X-rays and gamma rays.

A region of space where gravity is so strong that nothing, not even light, can escape from it. Black holes are the end product of massive stars collapsing under their own gravity.

The explosion of a star at the end of its life cycle. Supernovae can outshine entire galaxies and are key for dispersing elements into space.

A highly magnetized, rotating neutron star or white dwarf that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed when a beam points towards Earth.

A small rocky body orbiting the Sun, primarily found in the asteroid belt between Mars and Jupiter. Asteroids can vary in size from a few meters to hundreds of kilometers.

A highly energetic explosion that has been observed in distant galaxies. It is the most luminous event known to occur in the universe after the Big Bang.

The matter that exists in the space between the stars within a galaxy. It is composed of gas in ionic, atomic, and molecular form, as well as dust and cosmic rays.

The thermal radiation left over from the time of recombination in Big Bang cosmology, when the universe cooled enough to allow for the formation of neutral hydrogen atoms.

A celestial object composed of ice, dust, and rocky particles. When it approaches the Sun, a comet develops a coma—a fuzzy atmosphere—and sometimes a tail, due to the effects of solar radiation and solar wind.