The Life Cycle of a Star - Case Study Example

Evolution of Stars: Assumption of Physical Science Introduction Generally stars are to reach several stages from their initial formation to eventual deaths, and any stage in the lifecycle of a star is determined by the total mass and temperature of the star at its previous stage and the type of the mass that determines how the star will continue its burning and luminosity. It is the mass of the nebula in the initial stage of a star that determines whether the clouds of hydrogen gases dust will have enough gravity force to get condensed and squashed more and more to rise the temperature from the intermolecular collision and to start the nuclear fusion. At this stage the nebula may initiate two different lifecycles for stars depending on its size and mass. If the mass of the nebula resembles the size of the Sun, it turns into a star like the Sun of our solar system and this lifecycle yields Black Dwarf as end products. But if the mass of the nebula exceeds the mass of the Sun, it happens to turn into Blue Giant and eventually reaching a series of stages, yields Neutron Stars and Black Holes as end products. But in both cases in every stages of their life cycle, the mass of the nebula and the stars, its degree of gravity and subsequent temperature due to intermolecular collision and the nuclear fusion always determine the next stage of the cycle. (Source: The Life Cycle of a Star, www.scientology.org) Relative Mass-temperature-Lifespan of the Stars The stages in the lifecycle of a star are often named according to their characteristics, temperature, luminosity, size, density, etc. Also one phase is deferred from another phase with different intervals and lifespan of the phases and stellar masses. A comparative view of the mass, life-span, size and temperatures of the stars are given in the following table: (Source: The Life Cycle of a Star, www.scientology.org) Stellar Lifecycle in Hertzsprung-Russell (HR) Diagram Brightness and colour of a star is the measure of the temperature inside the star. Stars may appear in red, blue and yellow colours depending on the temperature inside the star. H-R diagram (Hertzsprung Russell Diagram) is the graphical representation of what we are observing and our theoretical knowledge about the stars. It is a temperature versus brightness graph. On the X axis the temperature is plotted while on the Y axis the brightness is plotted. From the above graph it is clear that at about 40000 K temperature the luminosity will be more than 10000 and the star colour will be blue. As the time passes the temperature gets reduced and the blue colour gradually approaches red. The HR Diagram in General, A schematic Hertzsprung-Russell (HR) Diagram (Hertzsprung - Russell diagram and Stellar Evolution, 2003) Stars with more masses will have shorter life whereas stars with less mass will have longer life. The Figure given below shows examples of stellar evolution curves for stars of 1.6 and, 2.0 solar masses. In the following figure the blue lines presents the collapsing of a Protostar. Generally it is called Hayashi Tracks. Now the green curve signifies the lifetime of the stellar evolution. “Once the star stops burning hydrogen in its core, it begins to expand, and moves off the main sequence towards the upper right (the giant region). The more massive stars sit on the hotter portion of the main sequence, live shorter lives than the less massive stars, and become larger giants” (Hertzsprung Russell Diagram And Stellar Evolution, 2003) Schematic Stellar Evolution (Hertzsprung Russell Diagram And Stellar Evolution, 2003) Nebula and Protostar: the Beginning of a Star Stars are formed from Nebulas, clouds of gases and dust, which condenses in the deeper parts of space. However, it is difficult to explain the initial step in the star formation. In this step of the formation of a star, several factors, such as mass, gravity, temperature of the nebula, play significant roles to initiate the whole process of formation. In the first place, if the mass of the nebula is so huge –especially around the mass of the Sun of our Solar System- its gravity will be sturdy enough to condense and, at the same, produce a high temperature. Due to the gravity, huge blocks of dense gas clouds begin to collapse at the beginning of stellar evolution, which may result in the conversion of gravitational energy into heat energy, which will warm the centre of the gas blocks. When the centre gets heated up microwave radiations may be started to liberate which will pass through the gas and dust blocks. This stage of stellar evolution can be called as Protostar. Normally it is assumed that the temperature is not high enough to start the nuclear fusion at this stage. Star like the Sun and Blue Giant: the Secondary Stage In order to initiate the nuclear fusion the core temperature of the Protostar needs to reach around 10 to 12 million-degree C. In the core of a star, the gravity is sturdy enough to rise the temperature at this point. The heat at the centre of the star goes on increases as more and more gas and dust blocks collapses and at some stage the temperature at the centre may reach so high so that a process called nuclear fusion may take place (Nuclear fusion is the process of combining two hydrogen nuclei to form a helium nucleus resulting in the liberation of huge amount of energy in the form of heat and light). This stage of stellar evolution is referred as the T-Tauri. At this stage, the nebula turns into either a star like the Sun or a Blue Giant depending on the mass of the nebula. It takes nearly 100 million years to form a star like the Sun, if the mass of the nebula is similar to the mass of the Sun. In this stage, the core and the surface temperatures of the star are around 6000c and 15000000c (fifteen million degree). But if the mass of the Protostar is four or five times bigger than that of the Sun, it eventually turns into a Blue Giant. It normally takes 10000000 years to form. The lifespan of a Blue Giant is shorter than a star like the Sun. Within 10 to 100 million years the Blue Giant reaches its next stage, the Star takes 10 billion years. The core temperature and the surface temperature of a Blue Giant are 17000c and 27 million degree C. Red Giant and Super Red Giant: Tertiary Stage The tertiary stage in the stellar lifecycle starts with the exhaustion of the stock of hydrogen in a star. The secondary stage of stellar evolution may last very much long until the hydrogen content exhausted. When the hydrogen stock begin to exhaust the star will undergo various changes; the core will began to shrink, fusion process will be rapid and the luminosity or energy liberated will increases and the outer space of the stars will become cooler giving a red color to the light emitted. This stage is called red giant, which will shed some of the stellar masses at this period to become lighter. The shrinkage of the core continues and will result in a big explosion called super nova’. (Strobel, 1995) The tertiary stage may last with different life span. Generally a Red Giant with the mass equal to the Sun lasts longer than the Super Red Giant. A Red Giant lasts for about 5000 years, whereas the other lasts only for several days. Indeed, the core a Super Red Giant consists of iron molecules that are formed with the burning of atoms with larger atomic masses such as Neon, Silicon, Potassium, Calcium etc in the Blue Giant. The temperature at the core of the Super Red Giant is about 10 billion degrees when the surface temperature is 3000C only. In this stage, the Super Big Giant -with a contracting surface in 3000C and, at the same time, with a rapidly expanding core in 10 billion degree C- explodes to produce the White Dwarf Star or the Super Nova. Red Giants in the HR Diagram Stellar Deaths and End Products ‘After the supernova explosion if the components which have low mass (less than 1.4 times the mass of sun) will become white dwarfs. The components which have the mass more than 1.4 times that of the sun will become neutron stars (a stage in which neutrons and protons move freely inside the star) If the mass of the component is greater than 3 times as that of the mass of the sun the star will become a black hole. At this stage, the gravity will increase so high and no matter will escape from the attractive pull due to gravity. Thus the black hole will absorb everything in its vicinity, increase its mass gradually and thereby its gravitational pull also’. Even light may not be escaped from a black hole which will result in the dark nature of the black hole (Strobel, 1995) Conclusions Stars are often a mystery for the human generation because of its existence beyond the reach of the scientific world. The extreme heat and the huge distance from the earth made the study of stars more complicated. We don’t have the correct idea about the formation of stars yet. But we have some ideas about the different stages it undergoes during its life cycle like, Protostar, T-Tauri, Red giant, supernova, white dwarf, neutron stars or pulsars, black hole etc. the changes of star during its death periods depends on the mass of the star compared to the mass of sun. If the mass of the star is less than 1.4 times that of the sun it will become a white dwarf, if it is more than 1.4 times that of the sun it will become a neutron star and if the mass of the star is more than 3 times as that of the sun it will become a black hole. References Hertzsprung Russell DiagramAnd Stellar Evolution, (2003), Retrieved on July 13, 2009 from http://www.tim-thompson.com/hr.html Strobel Nick, (1995) Stages in the Life of a Star, Retrieved on July 13, 2009 http://www.maa.mhn.de/Scholar/star_evol.html Stellar evolution (2008), Retrieved on July 13, 2009 from http://www.google.com/imgres?imgurl=http://chandra.harvard.edu/edu/formal/stellar_ev/poster_horiz_med2.jpg&imgrefurl=http://chandra.harvard.edu/edu/formal/stellar_ev/&h=901&w=2400&sz=1035&tbnid=OAZNa1qZTWdjkM:&tbnh=56&tbnw=150&prev=/images%3Fq%3Dstellar%2Bevolution&hl=en&usg=__mJSeWnwxa5oLirUJnp-UYtu4OYU=&ei=-WJbSpK7D8WTkAXRmb3UBQ&sa=X&oi=image_result&resnum=4&ct=image The Life Cycle of a Star (2009), Retrieved on July 13, 2009 from www.scientology.org Read More

Generally, it is called Hayashi Tracks. Now the green curve signifies the lifetime of the stellar evolution. “Once the star stops burning hydrogen in its core, it begins to expand and moves off the main sequence towards the upper right (the giant region). The more massive stars sit on the hotter portion of the main sequence, live shorter lives than the less massive stars, and become larger giants” (Hertzsprung Russell Diagram And Stellar Evolution, 2003)

Schematic Stellar Evolution

(Hertzsprung Russell Diagram And Stellar Evolution, 2003)

Nebula and Protostar: the Beginning of a Star

Stars are formed from Nebulas, clouds of gases and dust, which condenses in the deeper parts of space. However, it is difficult to explain the initial step in star formation. In this step of the formation of a star, several factors, such as mass, gravity, the temperature of the nebula, play significant roles to initiate the whole process of formation. In the first place, if the mass of the nebula is so huge –especially around the mass of the Sun of our Solar System- its gravity will be sturdy enough to condense and, at the same, produce a high temperature. Due to gravity, huge blocks of dense gas clouds begin to collapse at the beginning of stellar evolution, which may result in the conversion of gravitational energy into heat energy, which will warm the centre of the gas blocks. When the centre gets heated up microwave radiations may be started to liberate which will pass through the gas and dust blocks. This stage of stellar evolution can be called Protostar. Normally it is assumed that the temperature is not high enough to start the nuclear fusion at this stage.

Starlike the Sun and Blue Giant: the Secondary Stage

In order to initiate the nuclear fusion the core temperature of the Protostar needs to reach around 10 to 12 million-degree C. In the core of a star, the gravity is sturdy enough to raise the temperature at this point. The heat at the centre of the star goes on increases as more and more gas and dust blocks collapse and at some stage, the temperature at the centre may reach so high so that a process called nuclear fusion may take place (Nuclear fusion is the process of combining two hydrogen nuclei to form a helium nucleus resulting in the liberation of the huge amount of energy in the form of heat and light). This stage of stellar evolution is referred to as the T-Tauri. At this stage, the nebula turns into either a star like the Sun or a Blue Giant depending on the mass of the nebula. It takes nearly 100 million years to form a star like the Sun if the mass of the nebula is similar to the mass of the Sun. In this stage, the core and the surface temperatures of the star are around 6000c and 15000000c (fifteen million degrees).   

But if the mass of the Protostar is four or five times bigger than that of the Sun, it eventually turns into a Blue Giant. It normally takes 10000000 years to form. The lifespan of a Blue Giant is shorter than a star like the Sun. Within 10 to 100 million years the Blue Giant reaches its next stage, the Star takes 10 billion years. The core temperature and the surface temperature of a Blue Giant are 17000c and 27 million degrees C.

Red Giant and Super Red Giant: Tertiary Stage
The tertiary stage in the stellar lifecycle starts with the exhaustion of the stock of hydrogen in a star. The secondary stage of stellar evolution may last very much longer until the hydrogen content exhausted. When the hydrogen stock begins to exhaust the star will undergo various changes; the core will begin to shrink, the fusion process will be rapid and the luminosity or energy liberated will increases and the outer space of the stars will become cooler giving a red colour to the light emitted. This stage is called the red giant, which will shed some of the stellar masses at this period to become lighter. The shrinkage of the core continues and will result in a big explosion called super nova’.

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