Main-sequence Star
Related Category: Astronomy: General
see Hertzsprung-Russell diagram.
More on Main-sequence Star
Hertzsprung-russell Diagram - [for Ejnar Hertzsprung and H. N.
Main-sequence stars/dwarfs
Entire range of values
White Dwarfs are not included in this system, but are usually denoted by a "D" - for example, DA indicates a white dwarf of spectral type A.
Main-sequence star
*For comparison, recall that the diameter of the Sun is 1.4 106 km, while that of the solar system is roughly 1.5 1010 km.
STAGE 1: AN INTERSTELLAR CLOUD ...
Main-sequence stars are called dwarf stars, but this terminology is partly historical and can be somewhat confusing.
Main-sequence stars with masses equal to or less than that of the sun. More generally, any star on or below the main sequence in the Hertzprung-Russell diagram.
Dyad ...
A main-sequence star with spectral type M. Red dwarfs are much fainter, cooler, and smaller than the Sun but are the most common type of star in the Galaxy, accounting for 70 percent of all stars. The nearest red dwarf, Proxima Centauri, lies just 4.
a low-mass, main-sequence star much smaller, cooler, and less luminous than the sun
red giant
a cool star near the end of its life cycle that has expanded to a size of a few dozen to a hundred times the diameter of the sun ...
Our Sun is a main-sequence star—it has been one for about 4.5 billion years and will continue to be one for another 4.5 billion years. It has the spectral classification of G2 V.
Seyfert Galaxy
A main-sequence star that rotates rapidly, causing a loss of matter to an ever-expanding shell.
White dwarfs are thought to represent the end point of stellar evolution for main-sequence stars with masses from about 0.07 to 10 solar masses. The composition of the white dwarf produced will differ depending on the initial mass of the star.
For a group of stars with the same temperature, the luminosity class differentiates between their sizes (supergiants, giants, main-sequence stars, and subdwarfs).
Main Sequence Stars - Young Stars ...
star formation (NASA Thesaurus) The collapse under gravity of molecular clouds of interstellar matter to form clusters of protostars, and the continuing collapse of the protostars to form main-sequence stars.
Sirius is composed of a main-sequence star and a white dwarf stellar remnant. They form a close binary, Alpha Canis Majoris A and B, that is separated "on average" by only about 20 times the distance from the Earth to the Sun -- 19.
A star during most of its life is called a "main-sequence star". It consists of a central core, convective and radiative zones, the photosphere, the chromosphere, and the corona.
What may be the first discovery of a planet orbiting a normal, Sun-like star other than our own has been announced by astronomers studying 51 Pegasi, a spectral type G2-3 V main-sequence star 42 light-years from Earth.
Now let's consider those main-sequence stars. The mass of a star determines most of the properties that that star will have during its lifetime, and the mass determines where a star is on the main sequence.
The V-band light from old populations (ellipticals, spiral nuclei and bulges) is about evenly split between red giants and main-sequence stars.
For this long period of time the Sun is called a main-sequence star but eventually the hydrogen in the centre will all have been converted into helium.
MASS-LUMINOSITY RELATION - Dependence of the luminosity of a main-sequence star on its mass. The luminosity increases roughly as the mass raised raised to the power 3.5.
For main-sequence stars with elemental abundances similar to the Sun, the conversion of H into He is equal for the two processes when a star is ~2 Msun. Below ~1.
The first detection of a planet orbiting a main-sequence star was announced to the astronomical community by Michel Mayor and Didier Queloz in 1995.
"There's evidence that this star is right on the cusp of becoming a main-sequence star. So basically, we're catching a star that is right at the point of becoming a main-sequence star, and it looks like it's caught in the act of forming planets." ...
It is not a main sequence star but a post-main-sequence star. These incredibly hot stars burn helium. These giants have the spectral type O or B and are very rare and very bright. Blue giants have at least 18 times the mass of the Sun.
The very hot, extended outer atmosphere of the sun and other cool main-sequence stars. The high temperature in the corona (l-2x 106 K) is probably caused by the dissipation of mechanical energy from the convective zone just below the photosphere.
Such a small dense object is the first phase of the collapse of the so-called main-sequence stars. First white dwarfs, as they continue to cool they become yellow dwarfs then red dwarfs. Finally they die completely and are known as black dwarfs.
These are indicators of magnetic activity in normal, main-sequence stars, and are generated by the same process here. The magnetic fields in these stars can be quite strong, because like all early pre-main sequence stars they are fully convective.
"Around these stars, we are seeing three to four times more planets out to a distance of about three AU - the distance of our asteroid belt - than we see around main-sequence stars.
" This condensation initiates a period of contracting and internal heating followed by a long period as a main-sequence star.
 See also: Star, Light, Sun, Mass, Earth
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