Astrophysics (Index)About

main sequence star

(MS, V, dwarf star)
(star burning hydrogen into helium in its center)

A main sequence star is a star in the phase of its life termed the main sequence (MS), which is when it is burning hydrogen into helium through the proton-proton chain or the CNO cycle at its center, its stellar core. Such stars fit on a diagonal region (roughly a line) on an H-R diagram, the region/line on the diagram also being referred to as the main sequence. For many stars, this is the majority of their fusion lifetime, e.g., billions of years for Sun-like stars.

The term main sequence star is also likely occasionally used in a general way for a star that has or will have a main sequence in its lifetime, even if it is before or after this phase, to distinguish it from, for example, brown dwarfs. The unqualified term dwarf star actually refers to any star that is not a giant star, generally a star in its main sequence. If qualified, it depends: a white dwarf is beyond its main sequence, a brown dwarf has no main sequence, but a red dwarf is indeed in its main sequence. The suffix V attached to the spectral type indicates a main sequence star, aka a dwarf star. (Thus, do not take V as an indication of a variable star: rather it is a luminosity class.) For example, the Sun's spectral type has been cited as G2V.

Before their main sequence, such stars are powered by gravitational collapse and termed pre-main-sequence stars. The time-length of a star's main sequence varies based upon the mass of the star, more massive (early) stars producing much more fusion, more than making up for the larger amount of hydrogen, resulting in a shorter main sequence. The resulting main sequence lifetimes vary from millions of years to hundreds of billions. After the main sequence, all but the smallest stars (generally, all larger than a red dwarf) proceed to giant-star phases (post-main-sequence stars), while it is presumed that red dwarfs, none of which are old enough to have left their extremely long main sequence, will simply cool down.

(star type,stellar evolution,H-R diagram)
Further reading:

Referenced by pages:
AB Pictoris (AB Pic)
A-type star (A)
asymptotic giant branch (AGB)
Algol (Beta Per)
B-type star (B)
binary neutron star (BNS)
bolometric correction
brown dwarf (BD)
convection zone
cosmic dust
chemically peculiar star (CP star)
Earth analog
extreme mass ratio inspiral (EMRI)
evolutionary track
extra-solar planet
F-type star (F)
FGK star
51 Pegasi b (51 Peg b)
galactic binary
galaxy main sequence
G-type star (G)
G-dwarf problem
giant star
globular cluster (GC)
gravitational potential energy
horizontal branch (HB)
hydrogen burning
helium star
Henyey track
HR 8799
H-R diagram (HRD)
Hyades Cluster
hydrogen (H)
instability strip
K-type star (K)
Kepler Telescope
Kelvin-Helmholtz mechanism
luminosity class
main sequence fitting
mass-luminosity relation
mass-radius relation
M-type star (M)
M dwarf
solar mass (MSun)
O-type star (O)
post-common envelope binary (PCEB)
planet demographics
pre-main-sequence star (PMS)
post-main-sequence star
proton-proton chain
red clump (RC)
red dwarf
red giant
red-giant branch (RGB)
rotation period
Schönberg-Chandrasekhar limit
supernova progenitor
spectral class
spectral type
spectroscopic parallax
standard candle
stellar core
stellar demographics
stellar evolution
stellar luminosity determination
stellar remnant
stellar structure
substellar object
surface gravity (g)
timescale (t)
Tolman-Oppenheimer-Volkoff limit (TOV)
turn-off point (TO)
Vogt-Russell theorem (VR theorem)
white dwarf (WD)
Wilson-Bappu effect
zero-age main sequence (ZAMS)