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The
main sequence of the Hertzsprung-Russell diagram is the
curve along which the majority of
stars are located. Stars on this band are known as
main-sequence stars or
dwarf stars.
This line is so pronounced because both the stellar classification and the luminosity depend only on a star's mass (to
zeroth order approximation) as long as it is Nuclear fusion
hydrogen—and that is what almost all stars spend most of their "active" life doing. These main-sequence (and therefore "normal") stars are called dwarf stars not because they are unusually small. They simply have smaller radii and are less luminous than the other main type of stars, the giant stars. "
White dwarfs" are a different kind of star which are indeed small.
The main sequence does not follow a completely even curve; this is primarily because of the observational uncertainties which mainly affect the distance of the star in question but range all the way to unresolved
binary stars.
However, even perfect observations would lead to a fuzzy main sequence, because mass is not a star's only parameter. Metallicity and—related—its Stellar evolution also move a star slightly on the main sequence, as do Binary star,
Stellar rotation, or
Stellar magnetic fields, to name just a few factors. Actually, there are very metal-poor stars (subdwarfs) that lie just below the main sequence although they are fusing hydrogen, thus marking the lower edge of the main sequence's fuzziness due to chemical composition.
Astronomers will sometimes refer to the "
zero age main sequence", or
ZAMS. This is a line calculated by computer models of where a star will be when it begins hydrogen fusion; its brightness and surface temperature typically increase from this point with age. Stars usually enter and leave the main sequence from about when they are born or when they are starting to die, respectively.
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 is a dwarf star with a spectral classification of G2 V. After the hydrogen supply in the core is exhausted, it will expand to become a red giant.
The total main sequence lifetime of a star can be estimated from its mass relative to the Sun's as follows:{{cite web | last = Richmond | first = Michael | url = http://spiff.rit.edu/classes/phys230/lectures/star_age/star_age.html | title = Stellar evolution on the main sequence | language = English | accessdate = 2006-08-24-->
\tau_{ms} \sim 10^{10} \cdot \left \frac{M_\bigodot}{M} \right ^{2.5}\mbox{ years}
where M_\bigodot is the mass of the Sun, M is the mass of the star and \tau_{ms} is the star's estimated main sequence lifetime in years. The lightest stars, of less than a tenth of solar mass, may last over a trillion years. However, this estimate poorly matches the lifetime of the heaviest stars, which last at least a few million years.
Main sequence data
The table below shows typical values for stars along the main sequence. The values of luminosity (L),
radius (R), and
mass (M) are relative to the Sun. The actual values for a star may vary by as much as 20-30%. The coloration of the stellar class column gives an approximate representation of the star's photographic color. A popular
mnemonic for memorizing the sequence is
List of mnemonics for star classification.
{| border="1" cellspacing="0" cellpadding="4"
|- bgcolor="#FFFFCC"!rowspan="2"|Stellar classification!Radius!
Mass!
Luminosity!Temperature!rowspan="2"]|-|align="center" bgcolor="#5785ff"|B5|align="center"|3.7|align="center"|5.4|align="center"|750|align="center"|15,200|
Pi Andromedae|-|align="center" bgcolor="#7ca5ff"|A0|align="center"|2.3|align="center"|2.6|align="center"|63|align="center"|9,600|
Vega|-|align="center" bgcolor="#b1ccff"|F0|align="center"|1.5|align="center"|1.6|align="center"|9.0|align="center"|7,200|[Gamma Virginis|-|align="center" bgcolor="#edf4ff"|G0|align="center"|1.05|align="center"|1.08|align="center"|1.45|align="center"|6,000|[Beta Comae Berenices|-|align="center" bgcolor="#fff6e9"|G5|align="center"|0.98|align="center"|0.95|align="center"|0.70|align="center"|5,500|[Alpha Mensae|-|align="center" bgcolor="#ffcb91"|K5|align="center"|0.75|align="center"|0.62|align="center"|0.18|align="center"|4,450|[61 Cygni|-|align="center" bgcolor="#ffae62"|M0|align="center"|0.64|align="center"|0.47|align="center"|0.075|align="center"|3,850|Gliese 185|-|align="center" bgcolor="#ff8a38"|M5|align="center"|0.36|align="center"|0.25|align="center"|0.013|align="center"|3,200|
EZ Aquarii|-|align="center" bgcolor="#f00000"|M8|align="center"|0.15|align="center"|0.10|align="center"|0.0008|align="center"|2,500|Van Biesbroeck's star|-|align="center" bgcolor="#d00000"|M9.5|align="center"|0.10|align="center"|0.08|align="center"|0.0001|align="center"|1,900|LP 647-013|}
See also
References
- Massey, Philip and Michael R. Meyer. "Stellar Masses." The Encyclopedia of Astronomy and Astrophysics. Ed. Paul Murdin. London: Institute of Physics Publishing Ltd and Nature Publishing Group, 2001. 3103-09. ISBN 1-56159-268-4
External links
- Table of Features of the "Life Zones" of Main Sequence Stars
- A java based applet for stellar evolution.
The
main sequence of the Hertzsprung-Russell diagram is the curve along which the majority of
stars are located. Stars on this band are known as
main-sequence stars or
dwarf stars.
This line is so pronounced because both the stellar classification and the
luminosity depend only on a star's mass (to
zeroth order approximation) as long as it is
Nuclear fusion hydrogen—and that is what almost all stars spend most of their "active" life doing. These main-sequence (and therefore "normal") stars are called dwarf stars not because they are unusually small. They simply have smaller radii and are less luminous than the other main type of stars, the giant stars. "White dwarfs" are a different kind of star which are indeed small.
The main sequence does not follow a completely even curve; this is primarily because of the observational uncertainties which mainly affect the distance of the star in question but range all the way to unresolved binary stars.
However, even perfect observations would lead to a fuzzy main sequence, because mass is not a star's only parameter. Metallicity and—related—its Stellar evolution also move a star slightly on the main sequence, as do Binary star, Stellar rotation, or Stellar magnetic fields, to name just a few factors. Actually, there are very
metal-poor stars (subdwarfs) that lie just below the main sequence although they are fusing hydrogen, thus marking the lower edge of the main sequence's fuzziness due to chemical composition.
Astronomers will sometimes refer to the "
zero age main sequence", or
ZAMS. This is a line calculated by computer models of where a star will be when it begins hydrogen fusion; its brightness and surface temperature typically increase from this point with age. Stars usually enter and leave the main sequence from about when they are born or when they are starting to die, respectively.
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 is a dwarf star with a spectral classification of G2 V. After the hydrogen supply in the core is exhausted, it will expand to become a red giant.
The total main sequence lifetime of a star can be estimated from its mass relative to the Sun's as follows:{{cite web | last = Richmond | first = Michael | url = http://spiff.rit.edu/classes/phys230/lectures/star_age/star_age.html | title = Stellar evolution on the main sequence | language = English | accessdate = 2006-08-24-->
\tau_{ms} \sim 10^{10} \cdot \left \frac{M_\bigodot}{M} \right ^{2.5}\mbox{ years}
where M_\bigodot is the mass of the Sun, M is the mass of the star and \tau_{ms} is the star's estimated main sequence lifetime in years. The lightest stars, of less than a tenth of solar mass, may last over a trillion years. However, this estimate poorly matches the lifetime of the heaviest stars, which last at least a few million years.
Main sequence data
The table below shows typical values for stars along the main sequence. The values of luminosity (L),
radius (R), and
mass (M) are relative to the Sun. The actual values for a star may vary by as much as 20-30%. The coloration of the stellar class column gives an approximate representation of the star's photographic color. A popular
mnemonic for memorizing the sequence is List of mnemonics for star classification.
{| border="1" cellspacing="0" cellpadding="4"
|- bgcolor="#FFFFCC"!rowspan="2"|
Stellar classification!Radius!Mass!
Luminosity!
Temperature!rowspan="2"]|-|align="center" bgcolor="#5785ff"|B5|align="center"|3.7|align="center"|5.4|align="center"|750|align="center"|15,200|
Pi Andromedae|-|align="center" bgcolor="#7ca5ff"|A0|align="center"|2.3|align="center"|2.6|align="center"|63|align="center"|9,600|Vega|-|align="center" bgcolor="#b1ccff"|F0|align="center"|1.5|align="center"|1.6|align="center"|9.0|align="center"|7,200|[Gamma Virginis|-|align="center" bgcolor="#edf4ff"|G0|align="center"|1.05|align="center"|1.08|align="center"|1.45|align="center"|6,000|[Beta Comae Berenices|-|align="center" bgcolor="#fff6e9"|G5|align="center"|0.98|align="center"|0.95|align="center"|0.70|align="center"|5,500|[Alpha Mensae|-|align="center" bgcolor="#ffcb91"|K5|align="center"|0.75|align="center"|0.62|align="center"|0.18|align="center"|4,450|[61 Cygni|-|align="center" bgcolor="#ffae62"|M0|align="center"|0.64|align="center"|0.47|align="center"|0.075|align="center"|3,850|Gliese 185|-|align="center" bgcolor="#ff8a38"|M5|align="center"|0.36|align="center"|0.25|align="center"|0.013|align="center"|3,200|EZ Aquarii|-|align="center" bgcolor="#f00000"|M8|align="center"|0.15|align="center"|0.10|align="center"|0.0008|align="center"|2,500|Van Biesbroeck's star|-|align="center" bgcolor="#d00000"|M9.5|align="center"|0.10|align="center"|0.08|align="center"|0.0001|align="center"|1,900|LP 647-013|}
See also
References
- Massey, Philip and Michael R. Meyer. "Stellar Masses." The Encyclopedia of Astronomy and Astrophysics. Ed. Paul Murdin. London: Institute of Physics Publishing Ltd and Nature Publishing Group, 2001. 3103-09. ISBN 1-56159-268-4
External links
- Table of Features of the "Life Zones" of Main Sequence Stars
- A java based applet for stellar evolution.
Main sequence - Wikipedia, the free encyclopedia
The main sequence is the name for a continuous sequence of stars that appear on a plot of color versus brightness for groups of stars. These color-magnitude plots are known as ...
Pre-main sequence star - Wikipedia, the free encyclopedia
A pre-main sequence star (PMS star, or PMS object) is a star in the stage when it has not yet reached the main sequence. It can be a T Tauri star or FU Orionis star (
Stars
... most of the lifetime of a star, the interior heat and radiation is provided by nuclear reactions near the center; this is phase of the star's life is called the main sequence.
main sequence - definition of main sequence by the Free Online ...
A major grouping of stars that forms a relatively narrow band from the upper left to the lower right when plotted according to luminosity and surface temperature on the Hertzsprung ...
Main Sequence Star
Main Sequence : The energy trying to expand the star is caused by fusion of hydrogen to form helium in the core. This is called hydrogen 'burning' but this is not burning ...
The Life of a Star
The nearest main sequence star to Earth, the Sun. Stage 5 - A star of one solar mass remains in main sequence for about 10 billion years, until all of the hydrogen has fused to form ...
main-sequence star definition of main-sequence star in the Free Online ...
main-sequence star: see Hertzsprung-Russell diagram Hertzsprung-Russell diagram [for Ejnar Hertzsprung and H. N. Russell ], graph showing the luminosity of a star as a function of ...
GCSE Physics: Main Sequence Stars
Tutorials, tips and advice on GCSE Physics coursework and exams for students, parents and teachers.
main sequence - Hutchinson encyclopedia article about main sequence
In astronomy, part of the Hertzsprung-Russell diagram that contains most of the stars, including the Sun. It runs diagonally from the top left of the diagram (hottest and brightest ...
Hertzsprung-Russell Diagram
Main Sequence on the Hertzsprung-Russell Diagram About 90% of the known stars lie on the Main Sequence and have luminosities which approximately follow the mass-luminosity ...
