Origin of cosmic magnetic fields

4 problems

• Do intergalactic magnetic fields carry net helicity?

  Open

  Magnetic fields produced in the early universe by processes that distinguish left from right would be twisted with a preferred handedness. Measuring that twist would point to their origin.

• Do beam-plasma instabilities drain blazar pair beams before they radiate?

  Contested

  The electron-positron beams made by gamma rays in empty space might lose their energy to the thin intergalactic plasma before emitting gamma rays. If so, the missing gamma rays would not require magnetic fields at all.

• Were cosmic magnetic seed fields primordial or astrophysical?

  Open

  Dynamos in galaxies can amplify a weak magnetic field, but they need a starting seed. The seed could come from the early universe or from the first stars and galaxies.

• What is the magnetic field strength in cosmic voids?

  Open

  Very high-energy gamma rays from distant galaxies create electron-positron pairs that should produce lower-energy gamma rays, but those are missing, which suggests magnetic fields deflect the pairs. This gives a lower limit on the field, but nobody has measured its actual value.