1 / 32

Announcements

Announcements. Exam 2 is scheduled for Thursday March 7. Tentatively will cover Chapters 3 – 5 and possibly Chapter 6. Sample Questions are posted

morey
Download Presentation

Announcements

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Announcements • Exam 2 is scheduled for Thursday March 7. Tentatively will cover Chapters 3 – 5 and possibly Chapter 6. Sample Questions are posted • Project topics are due before spring break (March 7). Decide on a topic and come talk to me about it. The topic can be anything of current cosmological interest. • 1st Quarter observing night tonight. Forecast is excellent but cold. Meet at the observatory at 6:00pm. Dress warm! Cancellation notice, if needed, will be posted on www.apsu.edu/astronomy.

  2. The Laws of Thermodynamics Zeroth Law is the basis for thermometry First Law is a statement of conservation of energy Second Law says any heat engine must exhaust some heat Third Law says you can never reach a temperature of absolute zero. This is a manifestation of quantum mechanics

  3. Five Minute Essay Driving your car to work sure seems like “winning” in thermodynamics: you are getting work out of the engine and thereby being transported around. Describe, in as much detail as you can, the thermodynamic processes involved in driving your car to work and how you lose overall.

  4. Light is an Electromagnetic Wave(although it can also be a particle called a photon)

  5. A Basic Wave Wavelength = l Frequency = f Speed = c

  6. Sources of Light Blackbody Light Any object that has temperature emits a blackbody spectrum. Since everything has a temperature, everything emits light The spectrum is called a Planck’s Spectrum

  7. Light also comes from electron transitions

  8. The Doppler Effect Watch Doppler Effect Car Horn video

  9. Brightness Versus DistanceAn Inverse Square Relationship If all stars had the same intrinsic luminosity, the brightest stars would be the closest ones. Unfortunately, stars do not come with the same intrinsic luminosity. Watch YouTube Size Comparison video.

  10. To find distance to an object using the apparent brightness you must also know intrinsic luminosity of the object The intrinsic luminosity of the most distant cosmological objects is one of the most important questions in cosmology

  11. Complicating factor: interstellar reddening Intervening gas and dust will absorb some of the light and scatter the blue light leading to reddening of the color. The more space the light has to pass through, the greater the effect

  12. The life of stars

  13. The Interstellar Medium Reflection Emission HII Region Absorption Nebulae

  14. The Birth of Stars

  15. Stars form in the coldest darkest places in nebulae

  16. Bok Globule Close-up

  17. Something Triggers Collapse and a protostar begins to form

  18. New Star Formation Shock

  19. The collapse from nebula to protostar How long the collapse takes depends on the mass. More massive stars form quickly.

  20. Protostars are shrouded in a dense cocoon Infrared can penetrate into the cloud to reveal the protostars

  21. Protostars continue to collapse until the core temperature reaches 10,000,000°

  22. Not all protostars will reach a core temperature of 10 million K Brown dwarfs aren’t much larger than Jupiter but they can have up to almost 80 times the mass of Jupiter

  23. Stars maintain themselves by hydrostatic equilibrium If energy output from the core is insufficient, the star contracts. As it contracts, it heats up according to the gas law: PV = nRT If energy output from the core is excessive, the star expands. This will be important in the late stages of life.

  24. Once a core temperature of 10 million K is reached, fusion begins The Proton-Proton Cycle The high temperature is needed to overcome the electric repulsion between the protons.

  25. Due to hydrostatic equilibrium, the luminosity depends on the mass The self-gravity depends on the mass. The gas pressure depends on the temperature. The temperature depends on the energy output from the core which eventually comes out as the luminosity of the star

  26. The Hertzsprung-Russell Diagram

  27. Lifetime of Stars

  28. Stellar Populations Population I Stars: like the Sun, relatively young. Lots of “metals” in them. Found in the disk (and some in the nuclear bulge) of the Milky Way Population II Stars: very old, upwards of 10 to 12 billion years old. Most are as old as the galaxy is. Very low “metal” content. Found in the halo and nuclear bulge of the Milky Way. Due to their age, only lower mass (<Msun) stars can be Pop II stars Population III Stars: the first generation of stars. No “metal” content. Theory predicts there shouldn’t be any left

  29. H – R Diagram of a relatively young cluster…The Pleiades An even younger cluster would still have protostars at the low end

  30. H – R Diagram of an Old Cluster…Globular Cluster

  31. Stellar Size and the H-R Diagram

  32. On an H-R diagram the mass increases as you move up the Main Sequence

More Related