AST 101 Intro to Astronomy: Stars & Galaxies

Transcription

1 REVIEW FROM LAST CLASS AST 101 Intro to Astronomy: Stars & Galaxies Do we have direct evidence for fusion in the Sun? ANNOUNCEMENTS: First MIDTERM on FRIDAY 02/27 YES! Neutrinos REVIEW FROM LAST CLASS Neutrinos: MADE BY HYDROGEN FUSION IN CORE Tiny masses Don t interact (almost) with other matter Come in 3 flavors (electron, muon, tau) The Sun produces electron-type neutrinos Early neutrino detectors measured 1/3 of the solar neutrinos that theoretical calculations predicted -! SOLAR NEUTRINO PROBLEM Solution to the solar neutrino problem with the Sudbury Neutrino Observatory (SNO) SNO captures all three types of neutrinos (electron, muon, tao) Detects the RIGHT numbers!! Solar neutrino solution leads to big physics advance (2002 Nobel Prize) : electron neutrinos can transform into muon and tau neutrinos on their way from the Sun to us.

2 UNGRADED/UNRECORDED Clicker Question (any answer is a good answer) How is the pace of the course? A. B. C. D. E. Way too slow Too slow About right Too fast Way too fast Could the neutrinos flowing through our bodies be a cause of cancer or other cellular damage? A. YES, because there are so many and they carry a lot of energy B. NO, because they don t interact with anything and just flow through C. MAYBE, it depends on if they are electron, muon or tau neutrinos. Could the neutrinos flowing through our bodies be a cause of cancer or other cellular damage? A. YES, because there are so many and they carry a lot of energy B. NO, because they don t interact with anything and just flow through C. MAYBE, it depends on if they are electron, muon or tau neutrinos. How does the number of neutrinos passing through your body at night compare with the number passing through during the day? A. B. C. D. About the same. Much smaller during the night. Much larger during the night. Neutrinos don t pass through our body.

3 How does the number of neutrinos passing through your body at night compare with the number passing through during the day? A. B. C. D. About the same. Much smaller during the night. Much larger during the night. Neutrinos don t pass through our body. Hydrostatic Equilibrium 4. What makes the Sun stable? To understand this, we have to look into the forces at work on the Sun. In gases, we have, roughly: Pull of gravity = Push of pressure PRESSURE = DENSITY x TEMPERATURE 1. A high pressure in the center results in a high temperature. 2.If really hot, NUCLEAR BURNING can supply more energy Why don t we get a runaway reaction? High PRESSURE at CENTER

4 The Solar Thermostat 5. What s inside the Sun? From the Center Outwards Core: Hydrogen fusing into helium, releasing energy in the form of gamma rays, neutrinos, and positrons Core temp = 15 million K, hot & dense from the gravitational weight of all that mass Nuclear fusion rate very sensitive to temperature. Radiation Zone Gamma ray photons leave the core and move into an area known as the Radiation Zone Neutrinos? They leave right away, no interaction Positrons? Quickly find electrons in the core to annihilate with. Photons only travel about 1 mm before being redirected in another direction T=10 million K. Meanderings of outbound photons Our gamma-ray photons random walk outwards (getting redirected with every step), gradually cooling Takes hundreds of thousands to a million years to get out!!

5 Photosphere Convection Zone At the top of the convection zone, the densities are now low enough that our photons can zoom away. Now downgraded all the way to visible energies Photosphere is the visible surface of the Sun T = only 5800 K Photons free - seen at Earth 8 min later Blackbody spectrum (T= 5800 K) + absorption from cooler gasses just on top Eventually, gas is cool enough (2 million K at the boundary) and becomes turbulent Convection: hotter regions rise, cooler regions sink Energy continues to work its way out - nearly 1 million years to get out Granulation: turbulent convection Appearance of the photosphere Size: ~ 1 Mm across (that s a Megameter!) Granulation Movie Typical granulations last only 8-15 minutes Movie covers 35 min Taken by G. Scharmer & G. Simon at the Swedish Solar Telescope 27,000 km Diameter of Earth

6 The Sun suddenly stops fusing hydrogen and loses its energy source. Which of the following is true? A. The core will start to collapse. B. The core will become cooler. C. Both A & B D. The Sun will appear fainter to us after 8 minutes. E. The Sun will not change in brightness, but we will see the granulation stop (after 8 minutes). The Sun suddenly stops fusing hydrogen and loses its energy source. Which of the following is true? A. The core will start to collapse. B. The core will become cooler. C. Both A & B D. The Sun will appear fainter to us after 8 minutes. E. The Sun will not change in brightness, but we will see the granulation stop (after 8 minutes).