From Earth, not one star that fits the stricter definitions of a red dwarf is visible to the naked eye.

Definitions and usage of the term "red dwarf" vary on how inclusive they are on the hotter and more massive end.

One definition is synonymous with stellar M dwarfs (M-type main sequence stars), yielding a maximum temperature of 3,900 K and 0.6 M☉.

Low-mass red dwarfs therefore develop very slowly, maintaining a constant luminosity and spectral type for trillions of years, until their fuel is depleted.

Because of the comparatively short age of the universe, no red dwarfs yet exist at advanced stages of evolution.

The energy generated is the product of nuclear fusion of hydrogen into helium by way of the proton–proton (PP) chain mechanism.

Hence, these stars emit relatively little light, sometimes as little as 1⁄10,000 that of the Sun, although this would still imply a power output on the order of 1022 watts (10 trillion gigawatts or 10 ZW).

As a result, red dwarfs have estimated lifespans far longer than the present age of the universe, and stars less than 0.8 M☉ have not had time to leave the main sequence.

[15][19] As the proportion of hydrogen in a red dwarf is consumed, the rate of fusion declines and the core starts to contract.

The gravitational energy released by this size reduction is converted into heat, which is carried throughout the star by convection.

The Big Bang model predicts that the first generation of stars should have only hydrogen, helium, and trace amounts of lithium, and hence would be of low metallicity.

With their extreme lifespans, any red dwarfs that were a part of that first generation (population III stars) should still exist today.

While the basic scarcity of ancient metal-poor red dwarfs is expected, observations have detected even fewer than predicted.

Part of this is due to the fact that even the nearest red dwarfs are fairly faint, and their colors do not register well on photographic emulsions used in the early to mid 20th century.

The study of mid- to late-M dwarfs has significantly advanced only in the past few decades, primarily due to development of new astrographic and spectroscopic techniques, dispensing with photographic plates and progressing to charged-couple devices (CCDs) and infrared-sensitive arrays.

Building primarily upon the Boeshaar standards, a group at Steward Observatory (Kirkpatrick, Henry, & McCarthy, 1991)[30] filled in the spectral sequence from K5V to M9V.

[36] Observations with HARPS further indicate 40% of red dwarfs have a "super-Earth" class planet orbiting in the habitable zone where liquid water can exist on the surface.

In 2006, an even smaller exoplanet (only 5.5 ME) was found orbiting the red dwarf OGLE-2005-BLG-390L; it lies 390 million kilometres (2.6 AU) from the star and its surface temperature is −220 °C (53.1 K; −364.0 °F).

[41] On 23 February 2017 NASA announced the discovery of seven Earth-sized planets orbiting the red dwarf star TRAPPIST-1 approximately 39 light-years away in the constellation Aquarius.

In spite of their great numbers and long lifespans, there are several factors which may make life difficult on planets around a red dwarf.

First, planets in the habitable zone of a red dwarf would be so close to the parent star that they would likely be tidally locked.

On the other hand, a theory proposes that either a thick atmosphere or planetary ocean could potentially circulate heat around such a planet.