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.
25 March 2024
What does a supernova remnant sound like? Although sound is a compression wave in matter and does not carry into empty space, interpretive sound can help listeners appreciate and understand a visual image of a supernova remnant in a new way. Recently, the Jellyfish Nebula (IC 443) has been sonified quite creatively. In the featured sound-enhanced video, when an imaginary line passes over a star, the sound of a drop falling into water is played, a sound particularly relevant to the nebula's aquatic namesake. Additionally, when the descending line crosses gas that glows red, a low tone is played, while green sounds a middle tone, and blue produces a tone with a relatively high pitch. Light from the supernova that created the Jellyfish Nebula left approximately 35,000 years ago, when humanity was in the stone age. The nebula will slowly disperse over the next million years, although the explosion also created a dense neutron star which will remain indefinitely.