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The Sun is the Solar System's star and by far its most massive component. Its large mass (332,900 Earth masses), [75] which comprises 99.86% of all the mass in the Solar System, [76] produces temperatures and densities in its core high enough to sustain nuclear fusion of hydrogen into helium. [77]
This number is likely much higher, due to the sheer number of stars needed to be surveyed; a star approaching the Solar System 10 million years ago, moving at a typical Sun-relative 20–200 kilometers per second, would be 600–6,000 light-years from the Sun at present day, with millions of stars closer to the Sun.
The observable universe contains as many as an estimated 2 trillion galaxies [36] [37] [38] and, overall, as many as an estimated 10 24 stars [39] [40] – more stars (and, potentially, Earth-like planets) than all the grains of beach sand on planet Earth. [41] [42] [43] Other estimates are in the hundreds of billions rather than trillions.
This is a list of star systems within 150–200 light years of Earth. [1] [2] [3] ... Stars in system Spectral type Apparent magnitude (V) Comments and references
Mass transfer leads to cases such as the Algol paradox, where the most-evolved star in a system is the least massive. [102] The evolution of binary star and higher-order star systems is intensely researched since so many stars have been found to be members of binary systems. Around half of Sun-like stars, and an even higher proportion of more ...
The Sun is 1.4 million kilometers (4.643 light-seconds) wide, about 109 times wider than Earth, or four times the Lunar distance, and contains 99.86% of all Solar System mass. The Sun is a G-type main-sequence star that makes up about 99.86% of the mass of the Solar System. [26]
Alpha Centauri is a triple star system, with its two main stars, A and B, together comprising a binary component. The AB designation, or older A×B, denotes the mass centre of a main binary system relative to companion star(s) in a multiple star system. [85]
The stars with the most confirmed planets are the Sun (the Solar System's star) and Kepler-90, with 8 confirmed planets each, followed by TRAPPIST-1 with 7 planets. The 1,033 multiplanetary systems are listed below according to the star's distance from Earth. Proxima Centauri, the closest star to the Solar System, has three planets (b, c and d).