AAIM: DO NOW: AHW:

AAIM: WHAT ARE STARS? DO NOW: 1. Take GALAXY HW AHW: 1. LAB #18 CHARACTERISTICS OF STARS DUE TOMORROW 2. TEST MONDAY/TUESDAY NEXT WEEK (ASTRONOMY UNIT) 3. REVIEW DUE THURSDAY

The H.R. Diagram

STARS

What are Stars? Large spheres of gas (Hydrogen and Helium)

Held together by gravity Produce tremendous amounts of ENERGY

What fuels a star? The Sun is composed of 75% Hydrogen and 25% Helium The process of Hydrogen fusing with Hydrogen to create Helium This is called nuclear fusion Young stars have more Hydrogen than Helium The Sun is composed of 75% Hydrogen and 25% Helium

What is Luminosity? Luminosity is the actual brightness of the stars compared with that of our sun This is sometimes referred to as absolute magnitude

Life cycle of Stars

Nebula Stars are “born” from clouds of gas and dust originating from the Big Bang

What is a protostar? A protostar is a swirling disk of matter in which gravity is pulling inward

Once fusion begins the protostar becomes a star A star is born! Once fusion begins the protostar becomes a star Gravity and pressure work against each other and the star remains stable

AAIM: FINISH STARS DO NOW: 1. TAKE OUT LAB # 18 AHW: REVIEW WILL BE COLLECTED THURSDAY

What determines the fate of stars? A stars fate depends on its initial mass

Main-Sequence Stars 90% of all stars are Main-Sequence How long they remain depends on their mass

Lower mass stars eventually become white dwarfs Higher mass stars become Neutron stars or black holes

What is the fate of our Sun? Main Sequence Star Low mass Eventually, our Sun will run out of “fuel” (Hydrogen)

With a lower temperature, the core of the Sun will expand It will become a Red Giant, and swell to 100 – 1000 times bigger than it currently is

It will engulf the orbits of Mercury, Venus, and possibly even Earth

The Core of the Sun will expand & eventually engulf Earth

After becoming a red giant, it will shed its outer layers and shrink This is called a planetary nebula

Finally, our Sun will become a White Dwarf White Dwarfs are very small (only about the size of planet Earth)

They are dim (low luminosity) They represent the last stage of the Sun’s energy (when all nuclear fuel has been used up)

Low- Mass stars become white dwarfs

The Evolution of our Sun

What about the big stars! High mass stars will become SUPER giants Eventually they will contract and explode This is called a supernova

This star exploded 15,000 yrs. ago Supernova Explosion This star exploded 15,000 yrs. ago

Most become neutron stars after exploding Others……become………..BLACK HOLES!!!!!!

Black Holes Black holes form when extremely massive stars collapse

Cygnus X-1 – Binary Star System                                               Black Hole

A Black Hole warps space time Event Horizon Singularity