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"
Northern Pluto
18 August 2023
Gaze across the frozen canyons of northern Pluto in this contrast enhanced color scene. The image data used to construct it was acquired in July 2015 by the New Horizons spacecraft as it made the first reconnaissance flight through the remote Pluto system six billion kilometers from the Sun. Now known as Lowell Regio, the region was named for Percival Lowell, founder of the Lowell Observatory. Also famous for his speculation that there were canals on Mars, Lowell started the search that ultimately led to Pluto's discovery in 1930 by Clyde Tombaugh. In this frame Pluto's North Pole is above and left of center. The pale bluish floor of the broad canyon on the left is about 70 kilometers (45 miles) wide, running vertically toward the south. Higher elevations take on a yellowish hue. New Horizon's measurements were used to determine that in addition to nitrogen ice, methane ice is abundant across Lowell Regio. So far, Pluto is the only Solar System world named by an 11-year-old girl.