..he units stated above reflect the absolute minimum amount of interstellar mass needed to form a star. In comparison Jupiter and Saturn lack enough mass needed to form a star (0.001 and 0.0003 solar masses respectively). Such objects must resemble enormous Jupiter-like planets.Jupiter would have to be approximately sixty times bigger to become a star...."
http://hypertextbook.com/facts/2001/Kell...
When the Sun becomes a white dwarf star is will be about as big as Earth is./ White dwarf stars have no nuclear fusion going on in the core. They are just radiating light because of conduction, cooling of and loosing heat until they lose so much heat and are not radiating much energy at all and become a black dwarf star.. White dwarf stars are the cores of low mass former main sequence stars. like the Sun
"...The central C-O core of the Sun, now stripped of its envelope and having a mass of only 0.54 Msun, evolves into a slowly cooling White Dwarf the size of Earth...."
http://www.astronomy.ohio-state.edu/~pog...
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Elaine say: Excluding brown dwarfs, black dwarfs, red dwarfs a star the size of the earth is most likely a white dwarf which was originally the size of our sun. It is also possible that the star is the core of a star that became a nova. The density of this star is enough to keep its solar system just as when our sun becomes a white dwarf the outer planets of our solar system will continue to orbit the sun.
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Gary B say: " Astronomers have determined a minimum stellar size, helping clarify the line between true stars and strange "failed stars" called brown dwarfs.
All stars should be at least 8.7 percent as wide as our own sun, with average brightnesses no less than 0.00125 percent that of Earth's star, researchers said. They further calculated that all stars likely have surface temperatures of at least 3,140 degrees Fahrenheit (1,727 degrees Celsius).
"That is where the smallest star lives," Todd Henry of Georgia State University told reporters June 3, 2013 at the 222nd American Astronomical Society conference in Indianapolis."
http://www.space.com/21420-smallest-star...
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cosmo say: It depends a lot on whether you consider a Brown Dwarf to be a star or not. To burn Hydrogen in the core, a star needs to have about 7% of the mass of the Sun. Jupiter is 70x too small.
But Brown Dwarfs can have masses between those of planets and 7% of the Sun.
In fact, Jupiter emits more radiation than it absorbs (powered by ongoing gravitational contraction).
White dwarfs the size of the Earth are EXTREMELY dense.
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