It seems that magnetic fields are present even in the space between galaxies and they are coherent (not randomly distributed) within a Mpc (Megaparsec1). A lower bound (the minimum value that the magnetic field should have) has been derived by observing blazars. Long story short, a blazar is an extremely bright galactic center that is throwing a relativistic jet directly at us.2 This very high energetic beam of gamma rays interacts with extragalactic background light and creates electron-positron pairs. Now, if no magnetic field were present, such pair would annihilate again to produce secondary beams of gamma rays. Instead, if there are magnetic fields in the extragalactic space, the electron and the positron, once created, would go their separate ways and never annihilate back to a photon. It looks like this is what is happening! Check the original paper here.
If these Mpc wavelength magnetic fields are present in the intergalactic space, what could have created them? Magnetic fields originated from processes within galaxies would not have had enough time to go that far (a Mpc is about three million light years!). I study the generation of magnetic fields in the primordial universe, during a period called inflation (for more details on inflation see my other project). The main problem of this (relatively old) idea, called magnetogenesis, is that in order to explain the magnitude of current magnetic fields, they had to be huge in the early universe (as the universe expands everything dilutes). In fact, they need to be so huge that they would dominate the primordial universe. We know that this was not the case. I proposed one way to avoid such issues in this article. For technical details check this review or a recent one.
Another interesting phenomena that would occur if such huge electromagnetic fields were present in the primordial universe is what it is known as the Schwinger effect. Electromagnetic fields become so strong that particle-antiparticle pairs can be created out of vacuum depleting the electromagnetic field. This effect is particularly interesting if the universe is expanding. I have provided intuitive explanations in this publication.
- Mega = a million times. Parsec (pc) = 3.3 light years. A pc is the typical separation between stars. Roughly 10 kpc (kiloparsec) is the typical length of a galaxy. Mpc is the typical separation between galaxies. ^
- More properly, a blazar is an Active Galactic Nuclei (AGN) with a relativistic jet that is pointing towards us. This is why it appears extremely bright. ^
