Chapter 29.3 Stellar Evolution

Essential Questions:

1. What is the relationship between ,ass and a star’s evolution?
2. What are the features of massive and regular star life cycles?
3. How is the universe affected by the life cycles of a star?

Vocabulary:

nebula

protostar

neutron star

pulsar

supernova

black hole

Basic Structure of Stars

Mass governs a star’s temperature, luminosity, and diameter.  Mass and composition determine nearly all of a star’s other properties.

Mass Effects

The more massive the star, the  greater the gravity pressing inward

A star maintains its size due to hydrostatic equilibrium.  This is maintained by gravity pushing in equally against the outward pressure from heat and nuclear reactions inside the star.

Fusion

Density and temperature increase toward the center of a star.  Nuclear fusion, which  occurs in the star’s center, generates energy.  Main sequence stars fuse hydrogen into helium.

Stellar Evolution

Life cycle of a Medium mass star

Nebula  Cloud of dust and gas

Protostar
A developing star, not yet hot enough for nuclear fusion to occur

https://en.wikipedia.org/wiki/Protostar

Main sequence star

https://upload.wikimedia.org/wikipedia/commons/8/8b/Morgan-Keenan_spectral_classification.png
Core temp is at least 10 million K and nuclear fusion occurs
Star is a stable size as gravity pushing in is offset by gas pressure pushing out

Red Giant
All hydrogen in core gets consumed so star collapses causing the temp. to increase
Forms b/c zone of nuclear fusion moves outward

Planetary Neblua
During the collapse from a red giant to a white dwarf, a glowing cloud of gases is emitted

White dwarf
Remains of low and medium mass stars
Extremely small star w/ density greater than any substance on Earth

Black dwarf
A white dwarf that has cooled such that it is no longer emitting light