Red Giants, White Dwarfs, the Sun, & Black Holes

A Red Giant is defined as a "large, old, luminous star; that has a relatively low surface temperature and a diameter large relative to the sun" by the American Heritage Science dictionary. A red giant's creation originates when the hydrogen in a star is converted into helium. This conversion produces light and other radiation. The heavier helium created "sinks" toward the center of the star and a "shell" of hydrogen is formed around the helium cluster. At this point, the star does not generate a sufficient amount of energy and pressure; which is necessary to support the outer layers of the star, because of the hydrogen depletion. The star then collapses and the star's temperature and pressure levels rise until the helium core can "fuse" into carbon. This causes the helium to burn and radiate energy. At this point, the star transforms into a Red Giant. Red Giants are mostly formed from a main sequence star. Therefore, our sun will become a red giant during its lifetime. Red Giants characteristically have a surface temperature of 2,500 to 3,500 degrees Celsius. Red Giants also have a diameter between 10 and 100 times larger than the Sun's diameter. The masses of Red Giants vary greatly. Red Giants that are formed from the most massive of stars are considered to be Red Supergiants. Red Giants are also believed to "pulsate" and are considered variable.

A White Dwarf star is what stars become after they have "exhausted" their supply of nuclear fuel. White Dwarf stars are formed from planetary nebulae, which are formed from Red Giants. After a star has undergone the planetary nebula stage, only the hot core of the star remains present, which leaves the star as a "young" White Dwarf. This "young" White Dwarf will continue its cooling process over a period of a couple billion years. White Dwarfs are detected as low-energy x-ray sources. White Dwarfs are normally half as massive as the Sun, but a small amount larger than the Earth. White Dwarfs are one of the densest "forms of matter". White Dwarfs are known to survive because of quantum mechanical principles and not internal fusion. Also, as a White Dwarf's mass increases, its size decreases. Therefore, its mass and size are inversely proportional.

Our Sun is known as a main sequence star. Therefore, the Sun will become a Red Giant. Then the Sun will transform into a planetary nebula and finally meet its fate when it becomes a White Dwarf. The Sun's diameter is 1,390,000 kilometers. The Sun is known to contain approximately 99.8% of the Solar System's total mass. The core of the Sun is approximately 15,600,000 degrees Kelvin and its surface is 5,800 degress Kelvin. Since the Sun is not a "solid body" it exhibits "differential rotation", which causes the Sun to rotate slower near its poles. The surface of the Sun is called the photosphere, which lies below the chromosphere. Above the chromosphere, there is a region known as the corona, which is only visible during a total solar eclipse. The Sun has "cool regions" that look darker compared to its surrounding areas. These "cool regions" are called sunspots and are a result of "interactions", which are not yet understood, with the Sun's magnetic field. If the Sun was not a main sequence star and was a massive star instead, then the Sun's fate would be to result in a black hole.

Black holes are "objects so dense that not even light can escape their gravity", which means that nothing can exit a black hole. In the time of Newton, scientists hypothesized that a an object like a black hole could exist, but Einstein's Theory of Relativity "more accurately describes" this phenomenon. Black holes are formed as a result of supernova explosions. It is claimed that black holes are produced as a Red Supergiant collapses. Some scientists who specialize in black hole research are Karl Schwarzchild, Jayant Narlikan, and Stephen Hawking. Since substantial evidence about black holes is limited, black holes continue to be a topic of interest and immense fascination.

~Lindsey~



Addition to this post:

Here is a link to a very good flow chart of a star's life cycle: http://www.classzone.com/books/earth_science/terc/content/visualizations/es2807/es2807page01.cfm?chapter_no=visualization.
This website is written by a textbook company so it should not be discredited by the fact that it is a ".com".

Below is an image of a star's developmental stages.


Image provided by http://www.tqnyc.org/NYC040808/stages_of_a_star.html.