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.
7 May 2026
A long time ago, in a distant galaxy, a massive star was destroyed in a supernova explosion. The light of this event travelled for tens of millions of years and reached Earth last week as Supernova 2026kid. The featured video shows a time-lapse over three nights of the host galaxy NGC 5907, an edge-on spiral also known as the Splinter or Knife Edge Galaxy, as the supernova appears and becomes brighter. (The occasional streaks are satellites in Earth orbit.) At its brightest, a supernova can outshine the sum of all other stars in its galaxy. Supernova 2026kid appears relatively dim, probably because we are seeing it through the edge-on disk of the galaxy. Such explosions typically happen about once per century in galaxies similar to the Milky Way, and their light can take months to fade away. The brightest supernova in recorded history was SN 1006; it is reported to have been brighter than Venus, and even visible in the sky during daytime.