stjärnorna

Stjärnorna, in Swedish meaning “the stars,” are luminous spheres of hot plasma whose energy is produced by nuclear fusion in their cores. They illuminate the night sky and serve as reference points for measuring distances in astronomy.

Stars form from cold, dense regions within molecular clouds. Under gravity, clumps collapse into protostars that heat up as they accrete mass. When core temperatures become sufficient, hydrogen fusion begins and the star enters the main sequence, where it spends most of its life. Stars grow, change, and eventually exhaust their fuel, following paths determined largely by their initial mass.

Stars vary widely in mass, temperature, and luminosity. Their surface temperature largely determines color: blue or hot O- and B-type stars; yellowish G-type like the Sun; red M-type stars. Most stars share a common internal structure: a core where fusion occurs, surrounded by radiative and convective zones, with a photosphere as the visible surface. They can also possess outer atmospheres such as chromospheres and coronae, visible in certain observations.

The life cycle depends on mass. Low- to intermediate-mass stars end as red giants and white dwarfs after shedding outer layers in planetary nebulae. High-mass stars end their lives in core-collapse supernovae, leaving neutron stars or black holes. These processes distribute heavier elements into the interstellar medium, contributing to the chemical evolution of galaxies.

Observations of stars employ a range of techniques and wavelengths. Parallax measures distances to nearby stars; spectroscopy reveals temperature, composition, and motion. Stars organize into galaxies and clusters and have played central roles in navigation, calendars, and culture across civilizations.