STARS

Notes - Huge bright balls of gas fueled by nuclear energy Stars Energy Source

• Nuclear Energy

• Nuclear Fusion of mainly Hydrogen into Helium atoms.

• Gives off electromagnetic radiation. – Light, heat and other forms of energy

Stars Nuclear Energy The Sun – Our The closest star to Earth • Medium size • Yellow • Main Sequence Star • 150,000,000 Km (93 Million miles) away. • 4.5 - 5 billion years old • Will last about another 5 billion years • Located near the edge of our disc shaped – The Milky Way

Stars are very far away

• The Sun is the closest star to Earth – 150,000,000 km away

• The next closest star is Proxima Centauri – 39,900,000,000,000 km away – 4.2 light years • The Sun

• Stars are extremely far away!!!

• The Sun is thousands of times closer to Earth than other stars

• Proxima Centauri Stars are classified by surface temperature - color

Class Color Surface Temp. Elements Examples of (degrees Celsius) detected stars O Blue Above 30,000 Helium 10 Lacertae Blue-white 10,000 - 30,000 Helium and Rigel, Spica B Hydrogen A Blue-white 7,500 - 10,000 Hydrogen Vega, Sirius Yellow- 6,000 - 7,500 Hydrogen and Canopus, F white heavier Procyon elements Yellow 5,000 - 6,000 Calcium and The sun, G other metals Capella Orange 3,500 - 5,000 Calcium and Arcturus, K Molecules Aldebaran Red Less than 5,000 Molecules Betelgeuse, M Antares Hertzprung–Russel (H-R) Diagram - a graph that shows the relationship between a star’s surface temperature and it’s brightness (/). Absolute Magnitude/Luminosity

The actual brightness of stars.

H-R Diagram with Luminosity, Temperature and Color of Stars Analyzing the H-R Diagram

Brightest Stars

Y-Axis Brightness

Dimmest Stars

Hottest Stars X-Axis Coolest Stars Temperature Shows temperature and luminosity of stars throughout their evolution.

Nebulae – Stellar Nurseries

• Giant clouds of gas and dust in space where stars form.

• New stars form from nuclear fusion of Hydrogen atoms into Helium atoms. Main Sequence Stars • Stars that are fusing hydrogen atoms into • . helium in their cores. – Make up about 90% of all stars in the universe

• Where stars spend most of their existence. – How long depends on the stars mass Life Cycle of Stars

Life span of a star depends on its size. – Very large, massive stars burn their fuel much faster than smaller stars – Their main sequence may last only a few hundred thousand years – Smaller stars will live on for billions of years because they burn their fuel much more slowly Eventually, the star's fuel will begin to run out. Red Giants/Super Giants

• Dying Stars in the last stages of their evolution • Helium atoms fuse to form Carbon atoms. • Stars expand and surface temperatures drop – forming Red Giants or Super Giants • Lasts about a few thousand to 1 billion years depending on the mass of the star

Low to Medium Mass Stars form White Dwarfs White Dwarfs

• The hot, dense left over core of a collapsed star.

• The outer layers of the star blow off into space forming a planetary . Low/Medium Mass Stars High Mass Stars Become Super Giants Produce iron (Fe) atoms in their cores Supernova • When Super Giants collapse, they trigger a Supernova – Supernova: The “death” of a high mass star by explosion. Remains of a Supernova

• Neutron Stars • Black Holes – Small, incredibly dense – Invisible objects in space balls of closely packed with gravity so great that neutrons. nothing, not even light, – Neutron Stars that rotate can escape. rapidly are called “pulsars”

High Mass Stars Stages of a Stars Life Cycle