... Credit Copyright: C. Barbieri (Univ. of Padua), NASA , ESA Explanation: A dim double star system cataloged as Gliese 623 lies 25 light-years from Earth, in the constellation of Hercules . ... On the right, the fainter Gliese 623b is 60,000 times less luminous than the Sun and approximately 10 times less massive. ... The lowest mass stars are classified as red dwarf stars , but even red dwarfs are massive enough to trigger hydrogen fusion in their cores to sustain their feeble starlight. ...