CTAO Science
Cosmic magnetic fields
Vast voids between galaxies host tiny magnetic fields that may be relics of the Big Bang, generated during the first microseconds of the existence of the Universe. If this is so, these fields carry information about the Universe just moments after its birth. The intergalactic magnetic fields influence gamma-ray signals from distant sources. CTAO measurement of this influence will help to answer the questions What are the properties of the intergalactic magnetic fields and are they of cosmological origin? What led to their generation right after the Big Bang?
Gamma-ray interactions with the EBL photons result in deposition of electron and positron pairs all over the Universe, including vast voids between galaxies. These pairs are electrically charged and their trajectories are deflected by such magnetic fields present in the voids. This effect is observable, because electrons and positrons emit detectable secondary gamma rays in interactions with the CMB photons.
The intergalactic magnetic field parameters, such as its strength and correlation length, are not yet measured. CTAO will be able to pinpoint the eld parameters and verify their cosmological origin. This measurement, combined with complementary measurements in the radio-band by SKAO and CMB data will establish a new cosmological probe, sensing the state of the Universe just instants after the Big Bang. Magnetic field generation in the Early Universe has most probably been driven by processes that are not described by our current knowledge. Several phenomena beyond the Standard Model of Particle Physics are observed in the present-day Universe such as dark matter and dark energy or asymmetry. Information on the physical processes in the Early Universe that may be obtained through new cosmological magnetic field probe will help us to understand the nature of these phenomena.
Measurement of the cosmological magnetic field may also help in resolving the long-standing problem of the origin of magnetic fields in galaxies and galaxy clusters. Such fields are known to be the result of dynamo amplification of pre-existing seed fields, but the nature and properties of these fields are not known. The cosmological magnetic eld can in fact be the seed eld for the galactic dynamos. Magnetic fields in the Early Universe excite primordial gravitational waves and later on they may affect the cosmological recombination of protons and electrons into atoms and leave an observable imprint on the CMB properties.
Magnetic fields are amplified today during the formation of galaxies and galaxy clusters. The amplified fields are detectable with radio telescopes like SKAO, through the Faraday rotation effect. All the known matter in the Milky Way resides in a small region at the bottom of a gravitational potential well produced by dark matter filling the galaxy which manifests itself only through its gravitational pull. The only way to tackle this problem is a Multi-Messenger approach between CTAO-SKAO and ET and LISA, which will search for the Stochastic GW Background.