Astronomy 162 - Stars, Galaxies, & the Universe episodes:

• January 27, 2006Lecture 17: The Evolution of High-Mass Stars

  What happens when a high-mass (more than 4 solar masses) Main Sequence

  stars runs out of Hydrogen in its core. At first the internal evolution

  looks like that of a low-mass star, but now we get first a Red Supergiant

  then a sucession of blue and red supergiant phases as different nuclear

  fuels are tapped by the star for its energy. This lecture describes

  the evolution of high-mass stars from the Main Sequence until their

  eventual ends.

  Recorded 2006 January 27 in 1008 Evans Laboratory on the Columbus campus

  of The Ohio State University.

  ...more

  

  ---

• January 26, 2006Lecture 16: The Evolution of Low-Mass Stars

  What happens to a low-mass star (less than 4 solar masses) when

  it runs out of core Hydrogen and must leave the Main Sequence.

  This lecture describes the changes inside a low-mass star after

  Hydrogen exhaustion through the Red Giant, Horizontal Branch,

  Asymtotic Giant, and Planetary Nebula phases. In the end, we will

  see the star's envelope and core go their separate ways, the

  envelope gently puffed off into space, briefly flowering as a

  Planetary Nebula, and the Carbon-Oxygen core collapsing into

  a White Dwarf.

  Recorded 2006 January 26 in 1008 Evans Laboratory on the Columbus campus

  of The Ohio State University.

  ...more

  

  ---

• January 25, 2006Lecture 15: The Main Sequence

  What are the properties of stars on the Main Sequence? This lecture

  discusses what happens to a star after it alights onto the Main

  Sequence, burning H to He in its core, and maintaining a state

  of Hydrostatic and Thermal Equilibrium. We will see how the mass

  of a star determines its location along the Main Sequence and

  influences its energy generation and internal structure. We finally

  introduce the nuclear timescale and derive the Main-Sequence Lifetime

  for stars, and discuss its consequences.

  Recorded 2006 January 25 in 1008 Evans Laboratory on the Columbus campus

  of The Ohio State University.

  ...more

  

  ---

• January 24, 2006Lecture 14: Star Formation

  How do stars form? The Sun is old and in Hydrostatic and

  Thermal equilibrium. How did it get that way? This lecture

  presents the basic steps of star formation as a progress from

  cold interstellar Giant Molecular Clouds to Protostars in

  Hydrostatic Equilibrium, and then Pre-Main Sequence evolution

  which ends in ignition of core Hydrogen fusion and establishing

  Thermal Equilibrium on the Zero-Age Main Sequence.

  Recorded 2006 January 24 in 1008 Evans Laboratory on the Columbus campus

  of The Ohio State University.

  ...more

  

  ---

• January 23, 2006Lecture 13: Energy Generation and Transport in Stars

  How do stars generate energy in their cores, and once made, how is

  that energy transported to the surface where it can be radiated away

  as Luminosity? This lecture revisits nuclear fusion and the Kelvin-Helmholz

  Mechanism, and discusses the 3 ways energy can be transported in stars:

  Radiation, Convection, and Conduction. This will lead us to the

  concept of Thermal Equilibrium in stars, which is the last main piece

  of stellar physics we need before we can address the question of how

  stars are formed and evolve in the rest of this Unit.

  Recorded 2006 January 23 in 1008 Evans Laboratory on the Columbus campus

  of The Ohio State University.

  ...more

  

  ---

• January 19, 2006Lecture 12: As Long as the Sun Shines

  How long can the Sun continue to shine, and what source of energy

  does it tap to keep shining? This lecture answers this question by

  introducing two important energy sources for stars: Gravitational

  Contraction otherwise known as the Kelvin-Helmholz Mechanism, and

  Nuclear Fusion. We will show that fusion of 4 Hydrogen nuclei into

  a Helium nucleus via the proton-proton chain liberates enough energy

  to provide for the Sun's Luminosity needs for about 10 Billion Years.

  Recorded 2006 January 19 in 1008 Evans Laboratory on the Columbus campus

  of The Ohio State University. Note: the recording mistakenly says

  January 18th. Oops.

  ...more

  

  ---

• January 18, 2006Lecture 11: The Internal Structure of Stars

  What are the physical laws that determine the internal structure

  of stars? We first introduce the Mass-Luminosity Relation for

  Main Sequence stars, as well as seeing how the mean density of stars

  differs for stars on different parts of the H-R diagram. We then

  introduce the Ideal Gas Law, which relates pressure, density, and temperature,

  and show how the internal structure of a star is determined by

  a continuous tug-of-war between internal pressure trying to blow

  the star apart, and self-gravity trying to make it collapse. The

  balance between the two is the state of Hydrostatic Equilibrium. How

  the balance is maintained, and what happens when it is tipped in

  favor of either will determine the appearance and subsequent evolution

  of the star. Recorded 2006 January 18 in 1008 Evans Laboratory on the

  Columbus campus of The Ohio State University.

  ...more

  

  ---

• January 17, 2006Lecture 10: Synthesis: The Herzsprung-Russell Diagram

  How are all of the observed properties of stars (Luminosity,

  Mass, Radius, Temperature and Spectral Type) related to one another?

  This lecture introduces the Herzsprung-Russell Diagram, a plot of

  Luminosity versus Temperature for stars that is our most powerful tool

  for unlocking the secrets of the stars.

  Recorded 2006 January 17 in 1008 Evans Laboratory on the Columbus campus

  of The Ohio State University.

  ...more

  

  ---

• January 13, 2006Lecture 09: Stellar Spectra

  What do the spectra of stars look like, and what can they tell us

  about stellar properties? This lecture introduces the idea of stellar

  color, gives a brief overview of the history of stellar spectroscopy,

  and introduces spectral classification and the main stellar spectral

  types OBAFGKMLT.

  Recorded 2006 January 13 in 1008 Evans Laboratory on the Columbus campus

  of The Ohio State University.

  ...more

  

  ---

• January 12, 2006Lecture 08: Stellar Masses & Radii

  How do we measure the masses and radii of stars? This lecture

  describes the three basic types of binary stars, and how each are

  used to measure the masses of stars. Details of how to measure

  stellar radii are beyond the scope of this class, but we briefly

  describe the direct measurements of stellar radii.

  Recorded 2006 January 12 in 1008 Evans Laboratory on the Columbus campus

  of The Ohio State University.

  ...more

  

  ---