Presentation on theme: "High energy Astrophysics Mat Page Mullard Space Science Lab, UCL Revision lecture."— Presentation transcript:
High energy Astrophysics Mat Page Mullard Space Science Lab, UCL Revision lecture
Revision lecture: This lecture: Quick race through the course! Intended to inspire you to look back through your notes!
1: What is high energy astrophysics? High energy because: –Photons emitted above 100 eV (X-ray sources) –Large energy density in photon field or magnetic field, (eg X-ray binaries, pulsars) –Large amount of energy stored in gravitational field (eg Black holes) Unusually high concentrations of energy
X-rays from stellar photospheres? Take the Sun. T=5800K XUIV R
accretion efficiency How much energy can we get from accretion compared to fusion? Energy released per unit mass of material accreted = GM/R Energy equivalent per unit rest mass = c 2 So we can consider the efficiency of accretion to be GM/(Rc 2 ) For a white dwarf this is ~ 1.5 x 10 -4 Fusion of hydrogen converts 0.007 of rest mass to energy so we could say this has an efficiency of 0.7%