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Evolution of Stars
 

Sizes, luminosity, and temperatures of stars differ greatly.

Giants radiate much more energy than ordinary stars - such as the Sun - because of their vast surface area, and in spite of the fact that their surface temperature is relatively low. On the contrary, the size of a standard red star is normally equal to one tenth of the Sun. Such stars are called dwarfs in contrast to giants. Stars may be giants or dwarfs at different stages of their evolution. A giant may become "old" and turn into a white dwarf. Apart from red giants and supergiants, white and blue giants are also commonly found throughout the Galaxy.

A spectral diagram is formed in the following manner. Spectral classes (or effective temperatures) are situated along the X-axis. Luminosities L (or absolute magnitudes M) are situated along the Y-axis. All the stars would be evenly spread throughout such a diagram if no dependencies between luminosities and their temperatures were to exist. However, several patterns are found in the spectral diagram. These patterns are known as sequences.

The majority of stars (around 90%) are located along a long narrow line on the diagram that is commonly referred to as the main sequence. It stretches from the top left corner (from blue supergiants) to the bottom right corner (to red dwarfs). The Sun belongs to a group of stars of the main sequence. The Sun's luminosity is adapted to be the universal measure of luminosity, and is equal to 1.

The points corresponding to giants and supergiants are situated above the main sequence, and to its right. White dwarfs are located in the left corner below the main sequence.

The position of stars on the Hertzsprung-Russel diagram varies depending on star age.

Stars spend the greater parts of their life spans as parts of the main sequence. Their color, temperature, luminosity and other parameters remain virtually unchanged during that period. However, before a star reaches this stable condition, while still a protostar, it exhibits a red color and a higher luminosity.

Stages of evolution of stars once they leave the main sequence are also relatively short. Typically, stars turn into red giants. The most massive stars become red supergiants. In this case, a star quickly grows in size while simultaneously increasing its luminosity. The star finishes its life in an efficient explosion, throwing off the outer blanket.

This model represents a portion of Hertzsprung-Russel Diagram. Spectral temperatures of stars in degrees Kelvin are situated along the horizontal axis. Luminosity in solar units is displayed along the vertical axis.

Press "Run" button to observe how a protostar on the right side of the model starts moving towards the main sequence, glowing brighter and brighter. The star's age is indicated to the left. After some time (hundreds of millions or even billions of years) the star will leave the main Sizes, luminosity, and temperatures of stars differ greatly.

Giants radiate much more energy than ordinary stars - such as the Sun - because of their vast surface area, and in spite of the fact that their surface temperature is relatively low. On the contrary, the size of a standard red star is normally equal to one tenth of the Sun. Such stars are called dwarfs in contrast to giants. Stars may be giants or dwarfs at different stages of their evolution. A giant may become "old" and turn into a white dwarf. Apart from red giants and supergiants, white and blue giants are also commonly found throughout the Galaxy.

A spectral diagram is formed in the following manner. Spectral classes (or effective temperatures) are situated along the X-axis. Luminosities L (or absolute magnitudes M) are situated along the Y-axis. All the stars would be evenly spread throughout such a diagram if no dependencies between luminosities and their temperatures were to exist. However, several patterns are found in the spectral diagram. These patterns are known as sequences.

The majority of stars (around 90%) are located along a long narrow line on the diagram that is commonly referred to as the main sequence. It stretches from the top left corner (from blue supergiants) to the bottom right corner (to red dwarfs). The Sun belongs to a group of stars of the main sequence. The Sun's luminosity is adapted to be the universal measure of luminosity, and is equal to 1.

The points corresponding to giants and supergiants are situated above the main sequence, and to its right. White dwarfs are located in the left corner below the main sequence.

The position of stars on the Hertzsprung-Russel diagram varies depending on star age.

Stars spend the greater parts of their life spans as parts of the main sequence. Their color, temperature, luminosity and other parameters remain virtually unchanged during that period. However, before a star reaches this stable condition, while still a protostar, it exhibits a red color and a higher luminosity.

Stages of evolution of stars once they leave the main sequence are also relatively short. Typically, stars turn into red giants. The most massive stars become red supergiants. In this case, a star quickly grows in size while simultaneously increasing its luminosity. The star finishes its life in an efficient explosion, throwing off the outer blanket.

This model represents a portion of Hertzsprung-Russel Diagram. Spectral temperatures of stars in degrees Kelvin are situated along the horizontal axis. Luminosity in solar units is displayed along the vertical axis.

Press "Run" button to observe how a protostar on the right side of the model starts moving towards the main sequence, glowing brighter and brighter. The star's age is indicated to the left. After some time (hundreds of millions or even billions of years) the star will leave the main sequence, turning into a red giant. Finally, it will throw off the outer blanker and become a white dwarf. Press "Stop" to suspend the animation, and press "Reset" to return it to its initial state.

Use the input window to change the masses of stars. Note that if the star's mass is sufficiently large, it will end its evolution in an explosion of a supernova, later turning into a neutron star or even a black hole. An expanding tail of a planetary nebula surrounds such objects.

 
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