main sequence

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main sequence

The principal sequence of stars on the Hertzsprung–Russell diagram, running diagonally from upper left (high temperature, high luminosity) to lower right (low temperature, low luminosity) and containing about 90% of all known stars. A star spends most of its life on the main sequence. A newly formed star appears on the main sequence when it first achieves a stable state whereby its core temperature is sufficient for nuclear reactions to begin. It is then at age zero. The positions of the age-zero stars on the H-R diagram are specified by reference to the zero-age main sequence (ZAMS). As hydrogen is converted to helium, changes in chemical composition and stellar structure cause the star's position to shift slightly to the right from its zero-age position.

A star's position on the main sequence depends primarily on its mass, the more massive and thus more luminous stars occurring higher up the sequence. This gives a well-defined mass-luminosity relationship for main-sequence stars. The star's lifetime there also depends on its mass, the more massive stars having much shorter lifetimes: the lifetime is approximately

1010(M /M O )–3 years
where M and M O are the stellar and solar mass. After the star has consumed most of the helium in its core (see stellar evolution) it evolves away from the main sequence: its radius and luminosity increase and it eventually becomes a giant.

main sequence

[′mān ′sē·kwəns]
(astronomy)
The band in the spectrum luminosity diagram which has the great majority of stars; their energy derives from core burning of hydrogen into helium.
References in periodicals archive ?
The third type of potential donor in an AM CVn system is the evolved main-sequence star.
The main-sequence masses of stars of these spectral types are approximately [m.
Sarma, Rao & Abhyanker (15) discuss 30 such systems, noting that most secondaries are overluminous and over-large for their masses, compared to main-sequence stars of their spectral type.
For nearly a decade, Beta Pictoris has reigned as the only mature, main-sequence star with an encircling disk of dust - perhaps much like the disk from which our solar system evolved 4.
Fomalhaut, Beta Pictoris, and our own sun are main-sequence stars because they fuse hydrogen into helium to generate energy.
Either the star is so young that it hasn't finished contracting or so old--about 500 million years--that it has had time to expand its girth after becoming a main-sequence star.
Optical pictures of the cluster, taken by ground-based telescopes, detect mainly red giant stars and yellow main-sequence stars, whereas the ultraviolet image primarily spotlights hotter, less common stars that evolved from red giants by ejecting their outer atmosphere.