(Discussion – Star Stages; Video – HTUW – Extreme Stars – Part 4) Monday September 18, 2017 (Discussion – Star Stages; Video – HTUW – Extreme Stars – Part 4)

The Launch Pad Monday, 9/18/17 Explain how two competing processes allow a star to keep producing energy for billions of years. Nuclear fusion in the core of a star puts outward pressure on the star and tries to make it explode. Gravity pushes in on the star and tries to crush it. A stalemate is reach and this is what determines the star’s size. These two processes cancel each other and allow the star to exist at a certain size.

Picture of the Day! Monday, 9/18/17 This is Enceladus, a moon of Saturn. It is one of the leading candidates for life elsewhere in our Solar System.

Announcements Remediation for Quiz 2 runs through this Friday at 5:00. We will take Quiz 3 this Friday!

F7 F8 S2 QUIZ 2 Friday 9/12 TODAY 9/14 9/15 Last Day Accepted Assignment Currently Open Summative or Formative # Date Issued Gone Missing Day Last Day Accepted NASA Research Paper - Stars F7 9/12 TODAY Wednesday DE – Stars F8 9/14 Tomorrow QUIZ 2 S2 9/15 Friday

The sphere radiates long-wavelength (red) light. Star Stages Star Birth Stars are born in dark, cool, interstellar clouds of gas and dust called “nebulae.” Gravity contracts the cloud into a loose sphere and the temperature rises. The sphere radiates long-wavelength (red) light. It becomes a protostar.

Star Stages The Protostar The gravitational contraction of the gaseous cloud continues. The core eventually reaches a temperature of 10 million Kelvins. The thermonuclear fusion of hydrogen nuclei begins - they become helium nuclei . Tremendous amounts of energy are released. The outward pressure increases. The outward pressure is balanced by gravity pulling inward. The star becomes a stable “main- sequence” star.

Star Stages The Main-Sequence Stage Stars age at different rates. Massive stars use fuel faster and exist for only a few million years. Small stars use fuel slowly and exist for perhaps hundreds of billions of years. 90% of a star’s life is spent in the main sequence

Star Stages The Red Giant Stage Hydrogen fusion migrates outward. The star’s outer envelope expands. The star’s surface cools. The surface becomes red. The core is collapsing as helium is converted to carbon. Eventually all the star’s nuclear fuel is exhausted. Gravity begins to squeeze and contract the star.

The final stage of a star’s life depends upon it’s mass. Star Stages Burnout and Death The final stage of a star’s life depends upon it’s mass. In lower-mass stars (up to 0.5 solar masses), the red giant collapses and becomes a white dwarf.

The final stage of a star’s life depends upon it’s mass. Star Stages Burnout and Death The final stage of a star’s life depends upon it’s mass. In medium-mass stars (between 0.5 and 3 solar masses), the red giant collapses, expels its outer atmosphere into a “planetary nebula”, and becomes a white dwarf.

The final stage of a star’s life depends upon it’s mass. Star Stages Burnout and Death The final stage of a star’s life depends upon it’s mass. In massive stars (over 3 solar masses), a short life span terminates in a brilliant explosion called a “supernova.” The star’s interior condenses, and may produce a hot, dense object that is either: a neutron star, or a black hole.

Supernova1987A Supernova

H-R diagram showing stellar evolution

The Hertzsprung - Russell Diagram Red Giants and Supergiants are very large and very luminous, but have relatively cool surface temperatures. 90% of all stars are in the main-sequence stage. They are varied in their size, color, luminosity, and surface temperature. White Dwarfs are relatively dim, mid-temperature stars that are the remains of low- and mid-mass stars.

How the Universe Works: Extreme Stars Video Segment How the Universe Works: Extreme Stars Part 4 When a Star Dies

SLC Debrief (Notes should be taken during SLC Debriefs and kept in a section in your Science Binder) What’s inside of a white dwarf? What will happen to the earth when the sun becomes a red giant? Explain what is meant by the statement that star death creates new life. How long until our sun dies? What is gravity fighting with in our sun? What size classification is our sun? What does a high-mass star create after it explodes and dies?