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A galaxy is defined as a gravity-bound system of stars, stellar remnants, interstellar gas and dust, and dark matter.
A galaxy is a gravitationally bound system made of stars, stellar remnants, interstellar gas and dust, and dark matter. Its components are held together by gravity, and most of a galaxy’s mass is typically in the form of dark matter, while only a small fraction is visible as stars and nebulae. Galaxies vary widely in size, from dwarf galaxies with fewer than a thousand stars to the largest known galaxies containing on the order of hundreds of trillions of stars. Galaxies can be described by both their physical structure and their observable properties. They are commonly categorized by visual morphology—such as elliptical, spiral, or irregular—and may also be distinguished by special behaviors or features, including interactions with other galaxies, unusually high star-formation rates (starbursts), and the presence of an active galactic nucleus (AGN). Examples include the Milky Way (a spiral galaxy) and galaxies with energetic radio emission (radio galaxies), which are powered by jets from their central regions.
A galaxy is defined as a gravity-bound system of stars, stellar remnants, interstellar gas and dust, and dark matter.
Galaxies are classified by visual morphology (elliptical, spiral, irregular) and by notable properties such as interactions, starbursts, and active galactic nuclei.
Most of a galaxy’s mass is usually dark matter, while only a few percent appears as visible stars and nebulae.
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas and dust, and dark matter.
The interstellar medium is the gas and dust that exists between stars within a galaxy.
Dark matter is an unseen form of matter that contributes most of a galaxy’s mass through its gravitational effects.
Stellar remnants are the leftover objects from stars after they end their life cycles, such as white dwarfs, neutron stars, or black holes.
Galaxy morphology refers to the visual shape and structure used to classify galaxies, such as elliptical, spiral, or irregular.
An AGN is a compact, highly luminous region at a galaxy’s center whose energy output is dominated by processes near a supermassive black hole rather than by normal starlight.
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