Stars within 20 light-years

NASA -- larger image

Most nearby stars are very dim red dwarfs
-- like Gliese 623 A (M2.5V) and B (M5.8Ve)
at lower right -- invisible to the unaided
Human eye in Earth's night sky.

Astronomers find more nearby stars every year. Including Sol itself, at least 150 celestial objects (including white and brown dwarfs) are currently believed to be located within 20 light-years (ly) of Sol. Except for a few objects (such as Lalande 21185, Kapteyn's Star, and methane brown dwarf WISE J0254+0223) astronomers believe that Sol and most of its nearest neighbors were born in the Milky Way's "thin disk." A few (such as Barnard's Star and Kapteyn's Star) may be as much as 10 or more billion years old. By comparison, Sol is middle-aged at almost 4.6 billion years old, while younger stars include the Sirius binary system with perhaps around 300 million years.

Nearby Celestial Objects by Type, Number, and Mass

Minimum Solar-masses assumed for objects without mass estimates:
red stars (M=0.08); white dwarfs (D=0.5); and brown dwarfs (0.05).

At least two-thirds (88+ or 66+ percent) of the 150 or so objects found thus far to be located within 20 light-years are very dim red dwarfs, of which at least 39 (roughly half) may be flare stars and are likely to be relatively younger. As many as six stars within 20 ly may currently be brighter, larger, and more massive than Sol, but at least two (Sirus B and Procyon B) of the eight known nearby white dwarfs that are now much dimmer and smaller than Sol were once also brighter, larger, and more massive. In addition, 10 to 25 substellar brown dwarfs that are much more massive than the planet Jupiter have been detected, with and without stellar companions (see Gliese 229 b versus LP 944-20).

VLTI, ESO



Larger and jumbo images.



Although the larger bluish white
to orange dwarf stars are roughly
similar to Sol in size, red dwarfs
such as Proxima Centauri are not
much larger than Jupiter (more).

The volume of space lying within 20 light-years of Sol encompasses over 33,509 cubic light-years. Within that vast sphere, astronomers have been able to detect at least 50 Solar-masses of visible matter bound up in 138 luminous stars and weakly glowing white and brown dwarfs thus far. Hence, the local density of luminous mass is low, less than 2/1,000 (or 0.0015) of a Solar-mass per cubic light-year -- not even the mass of two Jupiter-sized planets.

NASA


Larger image.


Among Sol's neighbors within
20 ly, only 17 stars may
possibly be capable of
hosting Earth-type planets.

Within 20 ly of Sol, astronomers may have detected planets in the Solar System and around 12 other stars (Alpha Centauri B, 82 Eridani, Epsilon Eridani, Gliese 876 / Ross 780, CD-44 11909 / Gl 682, CD-46 11540 / Gl 674, CD-49 13515 / Gl 832, Gl 229, Groombridge 34 A, Kapteyn's Star229, Lalande 21185, Tau Ceti, and Wolf 1055 B (VB10, or Van Biesbroeck's Star), as of September 2014. Other than Sol itself, however, only around perhaps 17 stars out of 14 star systems (including such G stars as Alpha Centauri A) may possibly be capable of hosting Earth-type planets in stable orbits within their respective circumstellar habitable zones (CHZs). Within a CHZ orbit, liquid water may be possible on a planetary surface without tidal locking and orbital disruption from another celestial object.

------------------------------------- [Guide] -- [Full Near Star Map] -------------------------------------