Life Of A Star:
Stars expand as they grow old. A star the size of our Sun requires about 50 million years to mature from the beginning of its life to the collapse of its adulthood. Eventually the temperature reaches 15,000,000 C and nuclear fusion occurs in the cloud’s core. The cloud begins to glow brightly. At this stage, it contracts a little and becomes stable. It is now called a main sequence star and will remain in this stage, shining for millions or billions of years to come. As the main sequence star continues to glow , hydrogen in the core of the starc is converted into helium by what is known as nuclear fusion. When the hydrogen supply throughout the core begins to run out, the core becomes temperamental and compresses.
The outer shell of the star, which is still mostly made up of hydrogen, starts to expand itself. As it expands, it cools and begins to glow red. The star has now reached the red giant phase of it's life. It is red because it is cooler than it was in the main sequence star stage of the cycle and it is a giant because the outer shell has grown outward. All stars evolve the same way up to the red giant phase. The amount of mass a star has determines which of the following life cycle paths it will take after the red giant phase. Throughout the red giant phase of the cycle, the hydrogen gas in the outer shell of the star continues to smolder and the temperature in the core continues to gradually increase. At 200,000,000 degrees celcius the helium atoms in the core deliquesce to form carbon atoms.
The last of the hydrogen gas in the outer shell is pushed out to form a ring around the core. This ring is given the name planetary nebula. When the last of the helium atoms in the core are deliquesced into carbon atoms, the medium size star begins to die. Gravity causes the last of the star’s matter to collapse inbound and condensed. This is the white dwarf stage. At this stage, the star’s matter is extremely dense. White dwarfs give off a white hot light. Once all of their energy has left them, they no longer emit light. The star has now reached the black dwarf phase in its cycle in which it will forever remain. Once a massive star reaches their red giant phase, the core temperature continues to ascend as carbon atoms are formed from the melding of helium atoms. Gravity continues to evlove carbon atoms in sync as the temperature increases forming oxygen, nitrogen, and eventually iron. At this point, melding stops and the iron atoms start to take in energy.
This energy is eventually absolved in a powerful explosion known as a supernova. A supernova can light up the sky for weeks. The temperature in a supernova can reach 1,000,000,000 degrees celcius. The middle of a massive star that is 1.5 to 4 times as big as our Sun ends up in the state of a neutron star after the supernova. Neutron stars spin briskly giving off radio waves. If the radio waves are extruded in pulses (due to the star’s spin), these neutron stars are called pulsars. The centre of a massive star that has 8 or more times the weight of our Sun remains enormous even after the supernova. No nuclear fusion is taking place to support the centre of the star, so it is taken in by its own gravity. It has now become what is called a black hole which freely attracts any matter and energy that comes near or around it. Black holes are not visible. They are detected by the X-rays which are given off as matter falls into the hole.
