Small grouping of (typically 100 or less) stars, spanning up to a few tens of parsecs across, usually rich in very young stars.
Jets of material expelled from a protostar perpendicular to the surrounding protostellar disk.
Remnants of fragments of collapsing gas and dust that did not contain enough mass to initiate core nuclear fusion. Such objects are then frozen somewhere along their pre-main-sequence contraction phase, continually cooling into compact dark objects. Because of their small size and low temperature they are extremely difficult to detect observationally.
A graphical representation of a star's life, as a path on the H-R diagram.
Tightly bound, roughly spherical collection of hundreds of thousands, and sometimes millions, of stars spanning about 50 parsecs. Globular clusters are distributed in the halos around the Milky Way and other galaxies.
Loosely bound collection of tens to hundreds of stars, a few parsecs across, generally found in the plane of the Milky Way.
Stage in star formation when the interior of a collapsing fragment of gas is sufficiently hot and dense that it becomes opaque to its own radiation. The protostar is the dense region at the center of the fragment.
Swirling disk of gas and dust within which a star (and possibly a planetary system) forms. The "solar nebula," in the case of our Sun.
The central accumulation of material in the early stages of solar system formations, the forerunner of the present-day Sun.
Wave of matter, which may be generated by a star, which pushes material outward into the surrounding molecular cloud. The material tends to pile up, forming a rapidly-expanding shell of dense gas.
A grouping of anywhere from a dozen to a million stars which formed at the same time from the same cloud of interstellar gas. Stars in clusters are useful to aid our understanding of stellar evolution because they are all roughly the same age and chemical composition, and lie at roughly the same distance from Earth.
zero-age main sequence
The region on the H-R diagram, as predicted by theoretical models, where stars are located at the onset of nuclear burning in their cores.
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