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While Earth is the only place in the Universe known to harbor life, [10] [11] estimates of habitable zones around other stars, [12] [13] along with the discovery of thousands of exoplanets and new insights into the extreme habitats on Earth where organisms known as extremophiles live, suggest that there may be many more habitable places in the ...
However, some stars are nearly identical to the Sun and are considered solar twins. An exact solar twin would be a G2V star with a 5,778 K temperature, be 4.6 billion years old, with the correct metallicity and a 0.1% solar luminosity variation. [152] Stars with an age of 4.6 billion years are at the most stable state.
The types of stars generally considered to be potential hosts for habitable worlds include F, G, K, and M-type main-sequence stars. [7] The most massive stars— O , B , and A-type , respectively—have average lifespans on the main sequence that are considered too short for complex life to develop, [ 8 ] ranging from a few hundred million ...
The separation between stars in a binary may range from less than one astronomical unit (au, the "average" Earth-to-Sun distance) to several hundred au. In latter instances, the gravitational effects will be negligible on a planet orbiting an otherwise suitable star, and habitability potential will not be disrupted unless the orbit is highly ...
This is a list of exoplanets within the circumstellar habitable zone that are either under 10 Earth masses or smaller than 2.5 Earth radii, and thus have a chance of being rocky.
Red dwarfs [12] are the smallest, coolest, and most common type of star. Estimates of their abundance range from 70% of stars in spiral galaxies to more than 90% of all stars in elliptical galaxies, [13] [14] an often quoted median figure being 72–76% of the stars in the Milky Way (known since the 1990s from radio telescopic observation to be a barred spiral). [15]
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Distances can be measured within 10% as far as the Galactic Center, about 30,000 light years away. Stars have a velocity relative to the Sun that causes proper motion (transverse across the sky) and radial velocity (motion toward or away from the Sun).