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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 ...
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 ...
e. The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to ...
Stars can form orbital systems with other astronomical objects, as in planetary systems and star systems with two or more stars. When two such stars orbit closely, their gravitational interaction can significantly impact their evolution. Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy.
The most widely accepted model of planetary formation is known as the nebular hypothesis. This model posits that, 4.6 billion years ago, the Solar System was formed by the gravitational collapse of a giant molecular cloud spanning several light-years. Many stars, including the Sun, were formed within this collapsing cloud.
Simulated collision of two neutron stars. A stellar collision is the coming together of two stars [1] caused by stellar dynamics within a star cluster, or by the orbital decay of a binary star due to stellar mass loss or gravitational radiation, or by other mechanisms not yet well understood. Astronomers predict that events of this type occur ...
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 ...
Formation and evolution of the Solar System. There is evidence that the formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. [1] Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of ...