Red Dwarf Stars

Our Sun is such a familiar sight in the sky that you might think stars like our Sun are common across the Universe. But the most common stars in the Universe are actually much smaller and less massive than the Sun. The Universe is filled with red dwarf stars.
Red dwarf stars are the most common kind of stars in the Universe. These are main sequence stars but they have such low mass that they're much cooler than stars like our Sun.
Astronomers categorize a red dwarf as any star less than half the mass of the Sun, down to about 7.5% the mass of the Sun. Red dwarfs can't get less massive than 0.075 times the mass of the Sun because then they'd be too small to sustain nuclear fusion in their cores.
Red dwarfs do everything at a slower rate. Since they're a fraction of the mass of the Sun, red dwarfs generate as little as 1/10,000th the energy of the Sun. This means they consume their stores of hydrogen fuel at a fraction of the rate that a star like the Sun goes through. The largest known red dwarf has only 10% the luminosity of the Sun.
With such an efficient use of hydrogen, red dwarf stars with 10% the mass of the Sun are thought to live 10 trillion years. Our own Sun will only last about 10 to 12 billion or so.
You might be interested to know that the closest star to Earth, Proxima Centauri, is a red dwarf star. Unfortunately, these stars are so small and dim that they can't be seen without a telescope.