Universe

Life Cycles of Stars

The life cycle of stars describes the path of changes and transformations that stars experience throughout their lifespan of millions of years. Stars take on their path after being born in a stellar nebula, a giant cloud of gas and dust.

What Determines a Star's Life?

There are two main paths that stars can take that are dependent on the size of the new star. The bigger stars will become massive stars, while the regular ones become average stars. Average stars, like our Sun, will grow to be red giants, then shed their layers into a planetary nebula, leaving only the core to become a white dwarf. Massive stars will grow to be red supergiants, then burst into a supernova, which causes them to either become a neutron star or black hole depending on size.

The HR Diagram

The HR Diagram visualizes the relationship between a star´s luminosity and temperature. Luminosity is found on the y-axis while temperature is found on the x-axis. In the diagram, we can see four groups of stars. White Dwarves, Red Giants, Red Supergiants, and the Main Sequence. In the Main Sequence, we can find our Sun.

Temperature and Brightness

In the Main Sequence, temperature and luminosity are related in the way that as one increases, so does the other. The x-axis (temperature) is unique because it´s values increase from right to left.

The Four Corners

Each of the diagram´s four corners have labels. The top left corner is bright and hot, the top right corner is bright and cool, the bottom left corner is dim and hot, and the bottom right corner is dim and cool.

What are Galaxies?

A galaxy is a collection of stars, gas, and dust. There are more than 100 billion galaxies in our universe, and they can range in size anywhere from 10,000 to 20,000 light years across. There are three types of galaxies, spiral, elliptical, and irregular. They are classified by their shape and features.

Three Types of Galaxies

Spiral

Spiral glaxies have spiralling ¨arms¨ that portrude from a bulge in it´s center. The center is made of old stars while the arms are made up of young stars. Gas and dust is found throughout.

Elliptical

Elliptical galaxies are spherical in shape and have very bright centers. Stars are mostly old and found clumped together in globular clusters. Very little gas and dust.

Irregular

Irregular galaxies have no symmetry or definite shape. Stars are mostly young and scattered around. Full of gas and dust.

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