Life Cycle of a Star

Birth to Death and Rebirth

Created by Mrs. Marty Starling, 11/5/06

Interstellar Medium the Stellar Nursery

All stars start from the same material.

In space there is a swirling mixture of gases and dust.

After a cosmic event (ex. collision) this material condenses into a ball.

Protostar

When the material is compressed together it starts to heat up.

It soon gets hot enough to produce nuclear fusion –turn hydrogen into helium. This increase in energy causes the star to push outward.

This phase takes up to 500 million years for a star with a similar mass as our Sun to form.

Main Sequence Star

When the pressure pushing outward is in balance with the gravity pulling inward the star moves to the next phase.

Most stars spend the majority of their lives in this phase. A star with a mass the same as our Sun will be in this phase for 10 billion years.

Properties of Stars

Stars are balls of burning gas (mostly hydrogen and helium)

The speed at which stars burn their fuel determines their luminosity (brightness) and their temperature.

The mass of the star affects how fast or slow it burns its fuel.

High mass stars have a shorter lifespan than low mass stars.

Our Sun is considered a low mass star.

High Mass vs. Low Mass Stars

At this point the mass of the star determines where it goes next.

High mass stars burn through their fuel faster and turn into supernovas.

Low mass stars go into the yellow giant phase next.

Low Mass - Yellow Giant

In this phase the star burns up the hydrogen in its outer layers which compresses the helium in its core.

This compression causes an explosion in the core.

Low Mass - Red Giant

When the star runs out of hydrogen to convert to helium in its core, it starts to shrink.

As it shrinks the reaction makes it heat up and expand the outer part of the star.

The increase in heat allows the star to turn helium into heavier elements like carbon, oxygen and neon.

Low Mass –Planetary Nebula

Eventually it runs out of fuel in the core, and starts to burn off the outer layers and becomes a shell of gas.

At the center of this shell is a small, dense, bright star.

Low Mass - White Dwarf

This small, dense, very bright star is made of carbon and oxygen.

This star cannot heat up enough to burn this fuel, it cools off and is bright because of the stored energy from earlier phases.

Low Mass - Black Dwarf

The star continues to cool until all the energy has been released and then the low mass star ends its life at this stage.

High Mass –Red Super Giant

The star burns up the helium in the core causing it to shrink and then expand into a Red Super Giant phase.

High Mass - Supernova

High mass stars burn their fuel faster and heat up enough to burn carbon, and other elements and fuse into iron. Once they reach this stage they cannot burn iron.

The core collapses and causes a huge explosion sending the gas and solid material back into space to join the interstellar medium again.

High Mass –Neutron Star/Pulsar

After the supernova explosion a dense core of neutrons can remain.

This becomes a neutron star which gives off pulsing radio waves.

High Mass - Black Hole

If the neutron star does not collect material to grow into a new star then it collapses into itself creating a very dense star with so much gravity pulling in that nothing can escape it,

not even light.

Bibliography

Arny, Thomas. Explorations, An Introduction to Astronomy. New York: McGraw-Hill, 2006.

The Life Cycle of a Star. Sept. 10, 2006 <http://www.telescope.org/pparc/res8.html

The Life Cycle of a Star. Sept. 10, 2006 <http://spaceinfo.jaxa.jp/note/hoshi/e/hos01_e.html

Images from: http://images.search.yahoo.com/search/images/