STARS
Table of Contents
Different Types of Stars pg. 2
Hertzsprung-Russell Diagram pg. 3
What Happens When Stars Get Old? pg. 4
Different Types of Stars
There are different types of star classifications. Brightness, color, temperature, age and spectrum are some of the characteristics that scientists use to classify stars. Stars may have several types of classification throughout their lives.
Main Sequence Stars:
The longest star stage is the main sequence stage. A star becomes a main sequence star after it is born. During this stage hydrogen atoms form with helium atoms and produce enormous amounts of energy. As long as stars have enough hydrogen to bond with helium their size changes very little. They stay in this stage until they start to loose hydrogen.
Giants and Supergiants:
The next stage a star may enter in its life is the giant, supergiant phase. One type of star in the giant phase is a red giant. A red giant expands and cools after using all of its hydrogen. After using its hydrogen the star's center shrinks and the atmosphere grows large and cools. Red giants are ten times bigger than the sun and supergiants are 100 times bigger than the sun.
White Dwarfs:
When stars get old and enter their final stages they shrink. They can become the same size as the sun or smaller. These types of stars are called white dwarfs. White dwarfs have no hydrogen left in them. Since they have no hydrogen they cannot produce energy. However, white dwarfs can still shine for billions of years before dying.
Hertzsprung-Russell Diagram
Classifying Stars
Stars have been looked at and studied since ancient times. However, until 1911 scientists did not have a common way to study and classify stars. In 1911, Ejnar Hertzsprung used a graph to compare the brightness and temperature of stars. Hertzsprung was a Danish astonomer. Another astronomer, Henry Russell, from America also used a graph to compare and study stars. These astronomers ideas were combined into a tool now called the Hertzsprung-Russell diagram or H-R diagram. Astonomers use this tool to study stars today. The H-R diagram compares a star's surface temerature and absolute magnitude. Astronomers use this tool to study the life of a star and how it changes in temperature and brightness overtime.
Interpreting an H-R Diagram
An H-R diagram is fairly simple to read. The temperature of a star is listed along the bottom and the apparent magnitude is listed along the side. The brightest stars are located at the top of the H-R diagram. The dimmer a star is the lower it is located on the graph. The hottest stars are along the left of the graph and the coolest stars along the right. Most stars, as mentioned earlier, fall in the middle of the graph. These stars are the main sequence stars. Stars change their position on the H-R diagram throughout their lives.
What Happens When Stars Get Old?
When astronomers study stars using the H-R diagram they notice how long they stay in the main sequence. However, stars do get old and eventually die. As a star gets older several changes may occur. Stars can become supernovas, neutron stars, pulsars or black holes.
Supernovas
The hottest and biggest stars are known as blue stars. They have a shorter life than most stars because they give off energy more rapidly than other stars. When they die they may have a massive explosion called a supernova.
Neutron Stars and Pulsars
After a star explodes in a supernova the center may be squeezed together to form a neutron star. When all of the particles of a star are packed so tightly by gravity that they become neutrons it is known as a neutron star. If the neutron star is spinning it is known as a pulsar.
Black Holes
Material left from a supernova may also form a black hole. Black holes have so much gravity that no light can escape. It is hard for astronomers to find black holes because they do not give off light.