Hip Glossary: Star

Star – in old russian language 100 sun (sta Ra) A star is a massive, compact body of plasma in outer space that is held together by its own gravity and is sufficiently massive to sustain nuclear fusion in a very dense, hot core region. This fusion of atomic nuclei generates the energy that is continuously radiated from the outer layers of the star during much of its life span.

Astronomers can determine many of the properties of a star by observing its spectrum, luminosity and motion through space. Individual stars differ in their total mass, chemical composition, and age. The total mass of a star is the principal determinant in its evolution and eventual fate. Other characteristics of a star that are determined by its evolutionary history include the diameter, rotation, movement and temperature. A plot of the star’s temperature against luminosity, known as a Hertzsprung-Russell diagram (HR-diagram), allows the current age and evolutionary state of the star to be determined.

A star begins as a collapsing cloud of material that is primarily composed of hydrogen, with some helium and heavier trace elements. Once the stellar core is sufficiently dense, a portion of the hydrogen is then steadily converted into helium through the process of nuclear fusion. The remainder of the star’s interior carries energy away from the core through a combination of radiation and convective processes. At the surface this energy generates a stellar wind and is radiated out into space.

Once the hydrogen fuel at the core is exhausted, a star of at least 0.4 times the mass of the Sun expands to become a red giant, fusing heavier elements at the core, or in shells around the core. It then evolves into a degenerate form, recycling a portion of the matter into the interstellar environment where it will form a new generation of stars with a higher proportion of heavy elements.

Binary and multi-star systems consist of two or more stars that are gravitationally bound, and generally move around each other in stable orbits. When two such stars have a relatively close orbit, their gravitational interaction can have a significant impact on their evolution.