Your friends won't be happy about this (from the paper's Introduction) ..
Quote:
Intergalactic magnetic fields (IGMF) had not been measured until now, despite their importance for gamma-ray and cosmic-ray astronomy and their likely connection to the primordial fields that could have seeded the stronger magnetic fields observed in galaxies, Sun, and Earth. This is because IGMF are too small for conventional astronomical probes, such as Zeeman splitting or Faraday rotation.
Unlike the fields in galaxies, which are believed to have been amplified by the dynamo action of the large-scale convective motions of gas, the fields in voids remain low, close to their primordial values modified only by the relatively small contribution of the fields leaking out of galaxies (Kronberg 1994; Grasso & Rubinstein 2001; Widrow 2002; Kulsrud & Zweibel 2008).
The observational and theoretical upper bounds on IGMF constrain their magnitudes to be below 10∧−9 G (Barrow, Ferreira & Silk 1997), whereas any value above ∼10∧−30 G is sufficient to explain the ∼ μG Galactic magnetic fields generation by the dynamo mechanism (Davis, Lilley & T ̈ornkvist 1999).
One can detect such extremely weak fields using high-energy gamma rays (Aharonian, Coppi & Volk 1994; Plaga 1995).
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Chuckle, chuckle …
Interesting to see them putting a value to the field strengths.
Cheers
PS: That should read ten to the minus 9 Gauss and ten to the minus 30 Gauss.
Also, 1 Tesla (SI Units) = 1000 Gauss (cgs Units).