Survey of the Universe Tom Burbine

HW HW #4 and #5 are due the Wednesday after Spring Break

Reaction 4 protons → helium neutrinos + 2 positrons + energy Neutrino-virtually massless, chargeless particles Positron-positively charged electron – annihilated immediately by colliding with an electron to produce energy

Antiparticles Antiparticle – particle with the same mass and opposite electric charge Antiparticles make up antimatter Annihilation – when a particle and an antiparticle collide

Fusion reaction However, much more complicated than 4 protons → helium neutrinos + 2 positrons + energy

Called the Proton-Proton Chain Reaction

Deuteron – Deuterium (hydrogen with a neutron) nucelus

Neutrinos Neutrinos – almost massless particles No charge It takes a neutrino ~2 seconds to exit the Sun The neutrino was first postulated in 1930 by Wolfgang Pauli to preserve conservation of energy, conservation of momentum, and conservation of angular momentum during the decay of a neutron into a proton where an electron is emitted (and an antineutrino). Pauli theorized that an undetected particle was carrying away the observed difference between the energy, momentum, and angular momentum of the initial and final particles.

How was the Homestake Gold Mine used to detect neutrinos? A 400,000 liter vat of chlorine-containing cleaning fluid was placed in the Homestake gold mine Every so often Chlorine would capture a neutrino and turn into radioactive argon Modelers predict 1 reaction per day Experiments found 1 reaction every 3 days Newer detectors used water to look for reactions

What was the solar neutrino problem? Less neutrinos appear to be produced from the Sun than expected from models

Solution of Problem Neutrinos come in three types (slightly different masses) –Electron neutrino –Muon neutrino –Tau Neutrino Experiment could only detect electron neutrinos Fusion reactions in Sun only produced electron neutrinos Electron neutrinos could change into other types of neutrinos that could not be detected Neutrino oscillations – one type of neutrino could change into another type

Fusion The rate of nuclear fusion is a function of temperature Hotter temperature – higher fusion rate Lower temperature – lower fusion rate If the Sun gets hotter or colder, it may not be good for life on Earth

So how does the Sun stay relatively constant in Luminosity (power output)

Figure 15.8

Any Questions?