Random Letter of Wisdom Dear Mr. Planisek’s HPSC classes: Before you begin today- 1.This is one of the best classes that you will ever take. Keep that in mind. 2.Mr. Planisek is AWESOME! 3.Only 2 more days till Winter Break! (1 if you don’t count today, which I’m not!) Have fun! Very sincerely, ~SES

Life Cycle of a Star How is a star “born”? How does a star “die”?

Life Cycle of a Star Scientists look at different types of stars, studying the energy they give off and their composition to find indicators of how they age

Life Cycle of a Star Nebula – Large cloud of gas and dust spread out over a big region of space – Gravity pulls the dust and gas into a denser cloud – Temperature begins to rise → Nuclear Fusion – If there is enough mass (protostar), the balance between the outward pressure of fusion and the inward pull of gravity stabilizes the star

Birth of a Star

How are Different Types of Stars Formed? The mass of a star determines where it falls on the Main Sequence of the H-R Diagram

Stars formed from nebulas with large masses form bright, hot (blue) stars These stars burn out relatively quickly because they convert so much hydrogen into helium and use up their fuel very quickly

Stars with masses similar to Sun form stars that aren’t as bright or hot These stars will last much longer than blue stars because they don’t convert as much hydrogen to helium and their fuel lasts longer (even though there isn’t as much of it)

Stars with small masses produce cool stars that don’t give off much energy These stars are red and not very bright, but they can last for more than 100 billion years

What happens next?

Stars will remain stable as long as the outward push produced by the energy of fusion balances the inward pull of gravity

As fusion slows and the outward push decreases, gravity takes over and begins to shrink the star

The shrinking raises the temperature and fusion begins to occur outside of the core, which causes the star to expand

The core continues to shrink and gets hotter. Helium fusion starts and heavier elements are created

What happens next? Stars will remain stable as long as the outward push produced by the energy of fusion balances the inward pull of gravity Once the fuel of a star starts to run out and fusion slows down, the star will enter its final stages Just like the mass determines what the star turns into when it is born, it will determine what happens when it dies…

Death of Low/Medium Mass Stars

Low/Medium mass stars will remain as giants until their hydrogen and helium supplies completely run out and fusion stops

Death of Low/Medium Mass Stars Once fusion stops, the star shrinks and as it does, it is surrounded by a glowing cloud of gas (which used to be parts of the star) called a planetary nebula

Death of Low/Medium Mass Stars The remains of the hot core are all that is left eventually (White Dwarf) It still gives of thermal energy because it is hot, but no fusion occurs

Death of Low/Medium Mass Stars After a long period of time, the White Dwarf will cool and no longer glow. It will be called a Black Dwarf

Death of High Mass Stars

High mass stars turn into supergiants Supergiants have sections that are hot enough to produce heavier elements (up to iron)

Death of High Mass Stars When fusion stops, the huge gravity collapses the outer layers into the middle This results in a huge explosion called a supernova Elements heavier than iron are created and ejected into space

Death of High Mass Stars “Smaller” big stars turn into Neutron Stars Neutron Stars are the core of a big star after it has exploded into a supernova Huge gravity smashes protons & electrons together to form neutrons (+/- → 0)

Death of High Mass Stars “Bigger” big stars turn into Black Holes The gravitational pull of the remaining core is so strong that not even light (or any type of EM radiation) can escape!!!