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STARS. A. Nuclear Fusion. 1. A star is like a gigantic nuclear furnace. 2. The nuclear reactions inside the star convert hydrogen into helium by means of a process known as nuclear fusion. 3. Two Hydrogen atoms fuse together to form Helium.
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A. Nuclear Fusion 1. A star is like a gigantic nuclear furnace. 2. The nuclear reactions inside the star convert hydrogen into helium by means of a process known as nuclear fusion. 3. Two Hydrogen atoms fuse together to form Helium. 4. It is this nuclear reaction that gives a star its energy.
B.Classifying Stars 1.Scientists classify stars by: a. Temperature b. Brightness- Magnitude
C. Star Temperature 1. The color of a star tells us about its temperature. 2. Blue stars are the hottest, 7500°C- 30,000°C. 3. Red stars are the coolest, less than 3500°C. 4. Our sun is yellow in color, in the middle of the temperature scale, from 5000°C-7500°C.
Betelgeuse- Red Star- Coolest Rigel- Blue Star-Hottest CONSTELLATION ORION
Brightness or Magnitude 1.Stars are also classified by their brightness. 2. The brightness of a star as seen from Earth is called apparent magnitude. 3. The actual brightness of a star is called absolute magnitude. • Example: The SUN has an absolute magnitude of 4.8 when compared to the other stars. The SUN has an apparent magnitude of -26.8 because it is so close. The lower the number the brighter the star.
Another Example of absolute and apparent magnitude. B A Which light is brighter, A or B?
Light A is brighter than light B. • We see the apparent magnitude of the lights (how they look to us) • If lights A and B were next to each other they would look the same because the two lights are exactly the same. • Their absolute magnitude is the same. • Distance makes them look different. The same is true for stars. • Two stars could be the same brightness but their distance from us makes their brightness different.
Copy Questions on Page 52 Life Cycle of Stars 1. What is nuclear fusion? 2. What happens to create the stars energy? 3. How do scientists classify stars? 4. How would you describe blue stars? 5. How would you describe red stars? 6. How would you describe yellow stars like our Sun? 7. What is absolute magnitude? 8. What is apparent magnitude?
Life Cycle of our Sun • Stellar Nebula • Protostar • Main Sequence • Red Giant • Planetary Nebula • White Dwarf • Black Dwarf
Life Cycle of a Massive Star • Stellar Nebula • Protostar • Blue Giant • Red Supergiant • Supernova • Neutron Star (Pulsar) OR 7. Black Hole
A.Stellar Nebula 1. Stars begin their lives as clouds of dust and gas called a stellar nebula.
B. Protostar The gravity of a passing star or the shock wave from a nearby supernova may cause the nebula to contract. 1. Matter in the gas cloud will begin to come together into a dense region called a protostar. 2. As the protostar continues to condense, it heats up. 3. Eventually, it reaches a critical mass and nuclear fusion begins. 4. This begins the main sequence phase of the star. Our Sun is a main sequence star.
C. Main Sequence Stars 1. The life span of a star depends on its size. 2. Smaller stars, like the Sun, will burn for several billion years during their main sequence stage. 3. Our Sun is in its main sequence.
The main sequence is the longest part of a star’s life Average sized star like our Sun during main sequence. Massive star larger than our Sun during main sequence
D.Red Giant 1. Eventually, the star's fuel will begin to run out. 2. Our Sun will expand into what is known as a red giant. 3. This phase will last until the star exhausts its remaining fuel. 4. At this point, the star will collapse.
E. Planetary Nebula, White Dwarf and Black Dwarf 1. Most average stars will blow away their outer atmospheres to form a planetary nebula. 2. Their cores will remain behind and burn as a white dwarf until they cool down. 3. What will be left is a dark ball of matter known as a black dwarf.
A.Stellar Nebula 1. Stars begin their lives as clouds of dust and gas called a stellar nebula.
B. Protostar The gravity of a passing star or the shock wave from a nearby supernova may cause the nebula to contract. 1. Matter in the gas cloud will begin to come together into a dense region called a protostar. 2. As the protostar continues to condense, it heats up. 3. Eventually, it reaches a critical mass and nuclear fusion begins. 4. This begins the main sequence phase of the star. Our Sun is a main sequence star.
Blue Giant (Main Sequence) A massive star will become a Blue Giant during its main sequence stage. Blue stars are large and compact, this causes them to burn their fuel quickly which in turn makes their temperature very hot. These stars often run out of fuel in only 10,000 - 100,000 years.
Red Supergiant A red supergiant is an aging giant star that has consumed its core's supply of hydrogen fuel. It swells and becomes larger and cooler and collapses.
Supernova 1. If the star is massive enough, the collapse will trigger a violent explosion known as a supernova. 2. If the remaining mass of the star is about 1.4 times that of our Sun, it will collapse further to become a neutron star. 3. If the remaining mass of the star is more than about three times that of the Sun, it will collapse and what is left behind is an intense region of gravity called a black hole.
Massive Stars (Larger than our Sun) Become Red Supergiants.
OR It becomes a Black Hole This is an illustration, not an actual black hole!!
Life Cycle of our Sun • Stellar Nebula • Protostar • Main Sequence • Red Giant • Planetary Nebula • White Dwarf • Black Dwarf
Life Cycle of a Massive Star • Stellar Nebula • Protostar • Blue Giant- Main Sequence • Red Supergiant • Supernova • Neutron Star (Pulsar) OR 7. Black Hole
H-R Diagram Brighter Dimmer Hotter Cooler
H-R Diagram • The H-R Diagram shows: • Color • Size • Temperature • Absolute magnitude • The life cycle of stars. As stars age they move on the diagram. They become larger, smaller, cooler, hotter, brighter and dimmer.
Interactive Website • http://aspire.cosmic-ray.org/labs/star_life/starlife_main.html
