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Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or " star -forming regions", collapse and form stars. [1] As a branch of astronomy, star formation includes the study of the interstellar medium (ISM) and giant molecular clouds (GMC) as precursors to ...
One example of such a star-forming region is the Orion Nebula. Most stars form in groups of dozens to hundreds of thousands of stars. Massive stars in these groups may powerfully illuminate those clouds, ionizing the hydrogen, and creating H II regions. Such feedback effects, from star formation, may ultimately disrupt the cloud and prevent ...
A flat, rotating disc of stars and interstellar matter of which spiral arms are prominent components. A central stellar bulge of mainly older stars, which resembles an elliptical galaxy. A bar-shaped distribution of stars. A near-spherical halo of stars, including many in globular clusters.
Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the current age of the universe. The table shows the lifetimes of stars as a ...
The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System (as well as other planetary systems ). It suggests the Solar System is formed from gas and dust orbiting the Sun which clumped up together to form the planets. The theory was developed by Immanuel Kant ...
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of stars on and off the band are believed to indicate their physical properties, as well as their progress ...
Multiple star systems. A multiple star system consists of two or more stars that appear from Earth to be close to one another in the sky. [dubious – discuss] This may result from the stars actually being physically close and gravitationally bound to each other, in which case it is a physical multiple star, or this closeness may be merely apparent, in which case it is an optical multiple star ...
Stellar population. Artist's conception of the spiral structure of the Milky Way showing Baade's general population categories. The blue regions in the spiral arms are composed of the younger population I stars, while the yellow stars in the central bulge are the older population II stars. In reality, many population I stars are also found ...