main sequence

(redirected from Main-sequence)
Also found in: Dictionary, Wikipedia.

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 ?
Main-sequence stars are all powered by hydrogen fusion in their cores; they're fusing four hydrogen atoms to produce a single atom of helium, and releasing a huge amount of energy in the process.
The third type of potential donor in an AM CVn system is the evolved main-sequence star.
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.
Fomalhaut, Beta Pictoris, and our own sun are main-sequence stars because they fuse hydrogen into helium to generate energy.
The main-sequence stars of younger clusters include hot O and B stars, but being massive, they consume their nuclear fuel at a prodigious rate and thus have relatively short lives.
According to the authors' calculations, one such near-pass every 6,000 years or so is sufficient to maintain the present solar flux on Earth for the remainder of the Sun's main-sequence stage, around 5 billion years.
Stars that started out with plenty of mass burn rapidly and die young (after merely hundreds of millions of years), whereas stars that started out with less mass spend billions of years as main-sequence stars before becoming red giants.
These are main-sequence stars, but they are located well above the turn-off point .
Imaginova and Main-Sequence Software have teamed up to release the next level of desktop-planetarium software.
Five years ago astronomers used the Hubble Space Telescope to monitor the brightnesses of 34,091 main-sequence stars in the core of the globular cluster 47 Tucanae, in a hunt for giant planets transiting across their faces.
V471 Tauri comprises a main-sequence, K-type orange dwarf and a white dwarf in a 12 1/2-hour orbit.
This trend presumably happens because young main-sequence stars spin rapidly, and hence generate strong magnetic fields.