What is hydrostatic equilibrium in a star?
Hydrostatic Equilibrium. At every layer within a stable star, there is a balance between the inward pull of gravitation and the gas pressure.
What keeps the core of a star in equilibrium?
The cores of main-sequence stars are in hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward pressure of gravitational collapse from the overlying layers. The strong dependence of the rate of energy generation on temperature and pressure helps to sustain this balance.
What is the main sequence in astronomy?
In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell. Stars on this band are known as main-sequence stars or "dwarf" stars.
How do main sequence stars produce energy?
Main-sequence stars employ two types of hydrogen fusion processes, and the rate of energy generation from each type depends on the temperature in the core region. Astronomers divide the main sequence into upper and lower parts, based on which of the two is the dominant fusion process.
Are main sequence stars in equilibrium?
Stars in the main sequence have achieved a state of equilibrium, which means that the forces pushing in and the forces pushing out are equal and balance each other out. As long as the star has enough fuel in its core to continue its fusion reaction, the star will maintain equilibrium and stay a main sequence star.
Which forces are in equilibrium in a main sequence star?
A star's life is a constant struggle against the force of gravity. Gravity constantly works to try and cause the star to collapse. The star's core, however is very hot which creates pressure within the gas. This pressure counteracts the force of gravity, putting the star into what is called hydrostatic equilibrium.
What stages is a star in hydrostatic equilibrium?
During the Main Sequence phase, core hydrogen fusion creates the pressure (in the form of radiation pressure and thermal pressure) that maintains hydrostatic equilibrium in a star, so you should expect that when a star's core has become filled with helium and inert, the star will fall out of equilibrium.
What characteristics do main sequence stars have?
Main sequence stars are characterised by the source of their energy. They are all undergoing fusion of hydrogen into helium within their cores. The rate at which they do this and the amount of fuel available depends upon the mass of the star.
What is meant by hydrostatic equilibrium?
In fluid mechanics, hydrostatic equilibrium (hydrostatic balance, hydrostasy) is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force.
How is hydrostatic equilibrium in a star determined by mass?
The more the star is massive a star is, the greater the gravity pressing inward, and the hotter and more dense the star must be inside to balence it's own gravity. Infer how hydrostatic equilibrium in a star is determined by mass. The star's density increases, it's temperature rises, and it's luminosity increases.
What are the stages of a main sequence stars life?
All stars, irrespective of their size, follow the same 7 stage cycle, they start as a gas cloud and end as a star remnant.Giant Gas Cloud. A star originates from a large cloud of gas. ... Protostar. ... T-Tauri Phase. ... Main Sequence. ... Red Giant. ... The Fusion of Heavier Elements. ... Supernovae and Planetary Nebulae.
What defines a main sequence star?
Definition of main sequence : the group of stars that on a graph of spectrum versus luminosity forms a band comprising 90 percent of stellar types and that includes stars representative of the stages a normal star passes through during the majority of its lifetime.
What does the main sequence show?
In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell.
What is characteristic of a main sequence star quizlet?
What is characteristic of a main sequence star? The rate of nuclear energy generated in the hydrogen to helium fusing core equals the rate radiated from the surface.
What spectral type are main sequence stars?
The full spectral class for the Sun is then G2V, indicating a main-sequence star with a surface temperature around 5,800 K....Yerkes spectral classification.Luminosity classDescriptionExamplesIVsubgiantsGamma Cassiopeiae – B0.5IVpeVmain-sequence stars (dwarfs)Achernar – B6Vep8 more rows
Key Ideas
Main Sequence stars are those that "burn" Hydrogen into Helium in their cores.
Brighter with Age..
Main Sequence stars are in Hydrostatic Equilibrium. This requires a high central Pressure.
The Nuclear Timescale
How long a star can continue to generate energy by fusing H into He in its core depends upon how much fuel it has (total mass of the star), and how fast it is burning it (luminosity).
Main Sequence Lifetime
The Nuclear Timescale above depends on the Mass (M) and Luminosity (L). But, we know from the Mass-Luminosity Relation for Main Sequence Stars that
Consequences
If you see an O or B dwarf star, it must be relatively young as O and B stars evolve very rapidly and live for only a few Million years.
What is the main sequence of stars?
In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell. Stars on this band are known as main-sequence stars or dwarf stars.
What is the equilibrium of the cores of stars?
The cores of main-sequence stars are in hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward pressure of gravitational collapse from the overlying layers. The strong dependence of the rate of energy generation on temperature and pressure helps to sustain this balance.
Why does the main sequence band change as the star ages?
This effect results in a broadening of the main sequence band because stars are observed at random stages in their lifetime. That is, the main sequence band develops a thickness on the HR diagram; it is not simply a narrow line.
How is energy generated in the lower main sequence?
In the lower main sequence, energy is primarily generated as the result of the proton–proton chain, which directly fuses hydrogen together in a series of stages to produce helium. Stars in the upper main sequence have sufficiently high core temperatures to efficiently use the CNO cycle (see chart).
What is the lower edge of the main sequence fuzziness caused by?
These stars are fusing hydrogen in their cores and so they mark the lower edge of main sequence fuzziness caused by variance in chemical composition. A nearly vertical region of the HR diagram, known as the instability strip, is occupied by pulsating variable stars known as Cepheid variables.
What factors broaden the main sequence band on the HR diagram?
Other factors that broaden the main sequence band on the HR diagram include uncertainty in the distance to stars and the presence of unresolved binary stars that can alter the observed stellar parameters.
What is the difference between a dwarf and a giant star?
However, for hotter blue and white stars, the difference in size and brightness between so-called "dwarf" stars that are on the main sequence and so-called "giant" stars that are not, becomes smaller.
Key Ideas
Main Sequence Membership
- It must be in Hydrostatic Equilibrium(Pressure balances Gravity)
- It must be in Thermal Equilibrium(Energy Generation balances Luminosity)
- It must generate energy by "burning" Hydrogen into Helium in its core.
Brighter with Age...
- Since we have an ideal gas, Pressure = Density x Temperature: 1. Temperature: mean speeds of the nuclei 2. Density: number of nuclei per cubic centimeter 1. The remaining nuclei must move fasterto maintain the same high Pressure as before. 2. The gas at the center gets slowly hotter. 3. This causes fusion to run fasteras the temperature rises. The result is that Main Sequence stars …
The Main Sequence Is A Mass Sequence
- Low-Mass Stars: Cooler and Fainter
- High-Mass Stars: Hotter and Brighter
Internal Structure
- Nuclear reaction rates are very sensitive to core temperature: 1. P-P Chain: rate ~ T4 2. CNO Cycle: rate ~ T18! 1. Differences in internal structure. 2. Division into Upper and Lower Main-Sequences by mass.
Upper Main Sequence
- M > 1.1 Msun
- TCore> 18 Million K
Lower Main Sequence
- M < 1.1 Msun
- TCore< 18 Million K
The Lowest Mass Stars
The Nuclear Timescale
- We call this the Nuclear Timescale: 1. f = fraction of nuclear fuel available for fusion 2. e = efficiency of matter-energy conversion 3. M = mass of the star 4. L = luminosity of the star 1. tnuc= 10 Gyr given that f=10% of the Sun's H is available for fusion into He with a matter-energy conversion efficiency of e=0.7%
Main Sequence Lifetime
- L = M4
- High-Mass M-S Stars have shortM-S lifetimes
- Low-Mass M-S Stars have longM-S lifetimes