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A giant cloud of dust and gas in space, often the birthplace of stars and the remnants of a star's death.

The bending of the path of light from a distant object caused by a massive object between the light source and the observer, a prediction of Einstein's general theory of relativity.

The paradoxical observation that the night sky is dark despite the vast number of stars in the universe, which can be explained by the universe's expansion, finite age, and the absorption and re-emission of light by dust and gas.

Set of equations derived by Alexander Friedmann that show how the universe's expansion rate changes over time, based on the general theory of relativity and incorporating the curvature of the universe, energy density, and the cosmological constant.

A massive and extremely remote celestial object, emitting exceptionally large amounts of energy, and typically having a starlike image in a telescope, believed to be the active cores of distant galaxies.

A term introduced by Einstein in his general theory of relativity, representing an energy density filling space homogeneously, which can cause the expansion of the universe to accelerate.

The thermal radiation left over from the time of recombination in Big Bang cosmology, observed as a uniform glow across the sky.

A hypothetical set of various possible universes including the universe which we live in, often discussed in the context of theoretical cosmology.

A point at which density and gravity become infinite and space-time curvature becomes infinitely large. According to the Big Bang theory, the universe originated from a singularity.

The explosion of a star at the end of its life cycle, often resulting in the outshining of entire galaxies and the synthesis of heavy elements.

A region of space having a gravitational field so intense that no matter or radiation can escape, formed from the remnants of a large star after a supernova or by the merger of neutron stars.

An unknown form of energy that is hypothesized to permeate all of space, tending to accelerate the expansion of the universe.

The phenomenon where light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum, often indicative of the object moving away from the observer.

The theory that proposes the universe originated from a hot and dense initial point approximately 13.8 billion years ago and has been expanding since.

A celestial object of very small radius (typically 30 km) and very high density, composed predominantly of closely packed neutrons resulting from the collapse of a larger star after a supernova.

The philosophical consideration that observations of the universe must be compatible with the conscious and sapient life that observes it, implying that the universe's fundamental parameters are constrained by the conditions necessary for life.

The observation that galaxies are moving away from us at speeds proportional to their distance, which supports the theory of an expanding universe.

A highly luminous flash associated with an explosion in a distant galaxy, releasing a tremendous amount of energy in a short time period, considered the most energetic type of electromagnetic events known to occur in the universe.

A type of matter thought to account for approximately 85% of the matter in the universe, detectable through its gravitational effects on visible matter and cosmic structures.