Chapter 8 Protostars

4 Emission Nebulae –Interstellar plasma which emits red light 4 Reflection Nebulae –Dust particles which scatter and reflect light from nearby bright young stars

4 Planetary Nebulae –Ejected matter from a low mass star near the end of the star's life 4 Supernova Remnants –Ejected matter from a high mass star near the end of the star's life

The Birth of Stars 4 Stars begin their lives as an intersteller cloud. 4 This cloud collapses due to gravity into a dense core. 4 In about a million years a small, hot, dense core called a protostar forms.

8.1 Star Formation 4 Interstellar Medium –diffuse clouds of gas and dust –brought together to form a star –99% hydrogen

8.1.1 Gravitational PE and KE of a Sphere 4 Consider a uniform constant-density sphere.   = density = mass per unit volume 4 The total mass of material inside a sphere of radius r is...

4 The quantity M(r) is important since the shell that ends up at radius r will only feel a net force from material inside it.

8.1.2 Collapsing Clouds 4 What is the smallest-size clouds required for star formation? 4 How much mass is needed for star formation? 4 How long does it take to make a star?

4 Gravitational Potential Energy for Two Masses

4 Gravitational Potential Energy for a Cloud of Radius R

4 Kinetic Energy of a Cloud of Temperature T

8.1.2 Collapsing Clouds 4 The condition for gravitational binding is that the total energy is negative. 4 K + U < 0 4 To the chalk board...

4 Jeans Length –the minimum radius of a cloud for which the cloud is gravitational bound

4 Jeans Mass –the minimum mass of a cloud for which the cloud is gravitational bound

Free Fall Time 4 Once a cloud becomes gravitationally bound, it will begin to collapse. 4 The acceleration of a particle at a distance r from the center of the cloud is...

4 The free fall time is independent of the starting radius.

8.4 Evolutionary Tracks for Protostars 4 Evolutionary tracks are seen on H-R diagrams. 4 The evolutionary track of stars depend primarily on their mass. 4 Evolutionary tracks on the H-R diagrams can be explained with the familiar equation

What are T Tauri stars? 4 T Tauri stars are young, solar-like stars seen near many molecular clouds in our galaxy. 4 They are Pre-Main Sequence Stars on the HR Diagram. 4 They are active, variable stars.

4 Roughly half of T Tauri stars have accretion disk. 4 Most T Tauri stars are in binary star systems. 4 Simply put: T Tauri Stars are protostars that have masses around one solar mass. 4 Note: Fusion does not take place in protostars.

4 We see evidence of accretion disk around other stars.  For example,  Pictoris.