What Is a Star?

What is a star? A star is a huge shining ball of gas held together by gravity and produces a huge amount of light and energy. Stars are grouped in huge structures called galaxies. " There are 70,000 million, million, million stars in the known universe, according to a study by Australian astronomers. Its about 10 times as much stars as grains of sand on all the worlds beaches and deserts." ("Star survey reaches 70 sextillion."CNN.2003. 23 July.2003 http://www.cnn.com/2003/TECH/space/07/22/stars.survey/.

Stars like people, have lifecycles. They are born, go through several phases, and then they die. Life cycles of stars follow three general patterns. High-mass stars, intermediate stars, and low-mass stars. (Green, Paul J. "Star" Worldbook, 2002.)

"Intermediate-mass stars start out as a cloud that eventually develops into an intermediate star." (Green, Paul J. "Star" Worldbook, 2002.) This Process takes about 100,000 years until it then collapse into a proto star.

Intermediate stars go through about seven phases. Phase one, T-taun phase. The T-taun phase is when a star varies in brightness. This is why a star during this phase is often called a variable star. Second phase is called the main-sequence phase. During this phase the star has begun the longest part of its life as a producer of energy form hydrogen fusion. Third phase is the Red Giant phase. During this phase the star expands and its outer layers become cooler. The star becomes redder and because the stars surface area expands this causes the star to become brighter. Fourth is the Horizontal Branch Phase. During this phase the star steadily burns helium and hydrogen so its temperature, size, and brightness do not change. This phase lasts around 10 million years. Fifth is the asymptotic giant phase. During this phase all the helium in the core has fused, it then contracts making it hotter. Sixth is the White Dwarf phase. During this phase the star is now the remaining core from a planetary nebula. Lastly, is the Black Dwarf phase. At this point the star is too faint to be seen. A black dwarf is the end of the lifecycles of an intermediate- mass star.

Second lifecycle of a star is high-mass stars. A high-mass star forms from a proto star. They are hot and blue. High-mass star is 1,000 to 1 million times brighter than the sun. It is the most less common of the three but because they are so bright many can be seen.

A high-mass star also has phases that it goes through phase one is super novae. During this phase a star is doomed and cannot produce any more fusion energy to balance the force of gravity. Second phase is Neutron Stars. "After a Tye 11 supernova blast supernova blast occurs, the stellar core remains behind. If the core has less than three solar masses