Star
A star is a massive, self-luminous sphere of plasma held together by its own gravity. It shines by converting hydrogen into helium through nuclear fusion in its core, releasing energy across the electromagnetic spectrum.
Stars form in large clouds of gas and dust—called nebulae—where regions collapse under gravity, creating protostars. When core temperatures reach millions of degrees, fusion ignites, marking the birth of a star. Observatories like Hubble and missions such as NASA’s Infrared telescopes have imaged this process in action.
The majority (~90%) of stars are main-sequence stars, fusing hydrogen into helium. These include a broad range of masses—from red dwarfs (small, long-lived, faint) to blue giants and supergiants (massive, hot, and short-lived). Our Sun is a middle-aged G-type main sequence star.
As stars exhaust their hydrogen fuel, their evolution depends on mass. Lower-mass stars become red giants then white dwarfs. More massive stars undergo successive fusion stages, end in supernova explosions, and leave behind neutron stars or black holes.
Stars vary in brightness, size, and color. They are classified using spectral types (O, B, A, F, G, K, M) based on surface temperature and absorption lines. For example, O- and B-type stars are hot and blue; M-type are cool and red.
Stellar remnants include white dwarfs (Earth-sized cores of former stars), neutron stars (city-sized remnants of supernovae), and black holes (extreme-density objects from the most massive stars).
Stars are not static—many rotate, exhibit magnetic activity (like sunspots and flares), and broadcast stellar winds. Their lifecycle enriches the interstellar medium with heavier elements, seeding future generations of stars and planets.
Stars often exist in groups—binary or systems within star clusters and galaxies. Their properties are studied via brightness, spectra, parallax, variability, and statistical surveys by missions like Gaia and Kepler.
Sources
APODs including "Star"
A Planetary Nebula with Cosmic Buckyballs
4 June 2026
What is happening inside this unusual nebula? Planetary nebula Tc 1, captured here in exquisite detail by the James Webb Space Telescope, is the celestial site where buckyballs were first identified in 2010. Buckminsterfullerene — as buckyballs are officially called — is a molecule with 60 carbon atoms (C60) arranged in the shape of a soccer ball. The molecule is named for architect Buckminster Fuller because of its resemblance to the geodesic dome he helped popularize. Webb’s new data reveal where the C60 molecules live in this nebula, and the geometry is striking: they populate a thin spherical shell around the central star, visible here as the bright edge of the nebula’s glowing orange central region. Look closely near the nebula’s heart and a more perplexing feature emerges: a delicate structure shaped uncannily like an upside-down question mark, fitting punctuation for the many questions this nebula still poses.