1) describe what determines the size of a main sequence star and explain how sta
ID: 1865212 • Letter: 1
Question
1) describe what determines the size of a main sequence star and explain how stars get their energy and how stars obtain energy when all of the hydrogen is depleted.
2) describe the entire life cycle of a A) low mass B) medium (Sun-like) mass C) High mass star
3) describe the death of a A) low-mass B) medium mass C) high mass star and relate their mass to life expectancy
4) l describe what determines the fate of a star and how the life cycle of a star relates to all of us being made of "star stuff".
Explanation / Answer
1. Mass of the star in the main sequence is the key factor in determining its size.
More massive the star is, more is the gravitational force acting inwards resulting in hotter core. This in turn leads the nuclear reactions to take place at much higher rates in these stars.
When all the hydrogen is used up, it is converted to helium. At this point, the star starts to contract, becoming smaller. Due to this, the core contracts and becomes hotter. This leads the upper layers of the star expand, and as the star expands, it turns into a red giant.
2. a) For low-mass stars after the helium has fused into carbon, the core collapses again. The outer layers of the star are expelled. And a planetary nebula is formed by the outer layers. The core remains as a white dwarf and eventually cools to become a black dwarf.
b) This star is formed from an accretion disk. In these stars at some point, the helium will run out and gravity will take over, causing the inflated star to collapse on itself. This usually ends in a nova, and the core will remain and cool down, remaining as a white dwarf.
c) High-mass stars start in nebulae form and evolve and live in the Main Sequence. However, after the red giant phase it undergoes a supernova explosion. If the remainder of the explosion is 1.4 to about 3 times as massive as our Sun, it will become a neutron star.
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