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Loose ends and Magnetic Fields in Astronomy

Loose ends and Magnetic Fields in Astronomy. Exam tips – come to class! - Course Evaluations – come to class! - energy in fields - magnetism in matter - astronomical applications. Energy Density in EM Waves. The energy density, u , is the energy per unit volume

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Loose ends and Magnetic Fields in Astronomy

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  1. Loose ends and Magnetic Fields in Astronomy • Exam tips – come to class!- Course Evaluations – come to class!- energy in fields- magnetism in matter • - astronomical applications

  2. Energy Density in EM Waves • The energy density, u, is the energy per unit volume • For the electric field, uE= ½ εoE2 • For the magnetic field, uB = ½ μoB2 • Since B = E/c and

  3. Energy Density • The instantaneous energy density associated with the magnetic field of an EM wave equals the instantaneous energy density associated with the electric field • In a given volume, the energy is shared equally by the two fields

  4. Energy Density • The total instantaneous energy density is the sum of the energy densities associated with each field • u =uE + uB = εoE2 = B2 / μo • When this is averaged over one or more cycles, the total average becomes • uav = εo(E2)av = ½ εoE2max = B2max / 2μo

  5. Where does magnetism come from ???? Recall these equations:I=Q/t T=2πr/vL=mvrμ=IA (sub in the above, and A=πr2)Imagine a little circuit with an electron moving at a distance r from the nucleus of an atom. Combining these, we can show that: This is the magnetic moment of anelectron

  6. Where does magnetism come from ???? Now, because the angular momentum L for electrons isquantized, L=The smallest possible non-zero value of the magnetic moment is : Q: So, if all electrons have this unit of magnetic moment, why are not all substances magnetic ???

  7. EM in Astronomy

  8. Magnetic fields ‘rotate’ an electromagnetic wave. This is called Faraday Rotation, and it allows us to measure the magnetic field of interstellar space.

  9. This is the spiral galaxy M51 and its magnetic field. Studying the fields helps us understand how galaxies form and evolve.

  10. This is the jet of M87, evidence for a super massive black hole at the center of this galaxy.

  11. Sunspots are caused by strong magnetic fields on the surface of the sun. We can detect them on other stars currently!

  12. A supercomputer simulation of the reversal of earth’s magnetic field The earth’s magnetic field.

  13. Planetary formation needs to incorporate magnetic fields in the ‘protoplanetary’ disc. These are called MHD (magneto-hydro-dynamics simulations.

  14. Redshift of EM waves

  15. Galaxy distribution

  16. Large Scale Galaxy Distribution

  17. Computer simulations of large scale structure formation

  18. HDF and early galaxy formation

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