Red dwarfs are about 75% of stars, yet none is visible by eye

About three-quarters of the stars in the Milky Way are red dwarfs, small, cool stars between roughly a thirteenth and half the Sun’s mass, yet not one of them is visible to the naked eye from Earth.

That makes the night sky a biased sample. The stars you can see are mostly the galaxy’s rare bright ones, while its real majority needs a telescope. Stars like the Sun make up only about 8% of the galaxy, and very massive stars, up to about 150 times the Sun’s mass, are rarer still.

Nobody can count every star in the galaxy, so astronomers count the neighbourhood as completely as possible. The Research Consortium On Nearby Stars (RECONS) census of everything within 10 parsecs (32.6 light-years) found that 284 of 378 stars were red dwarfs: 75%. Only 19 were G-type stars like the Sun. The tally keeps shifting towards red dwarfs as faint ones are found: between 2000 and 2018 the number known within that distance rose by about 43%, while the counts of A, F, G and K stars did not change at all. Our nearest neighbour, Proxima Centauri, 4.2 light-years away, is one of them.

Small doesn’t mean short-lived. Red dwarfs burn their hydrogen so slowly that their lifetimes exceed the present age of the universe, so the galaxy’s commonest stars are also its most durable.

Nor are they quiet. Many have surfaces carpeted with strong magnetic fields and give off flares that may be a thousand times more energetic than typical solar flares; Proxima itself randomly brightens for hours at a time. That radiation could be devastating for the habitability of any planets orbiting them.