Reacción a "Reactions to the discovery of high-energy neutrinos emitted by an active galaxy"

IceCube has succeeded in observing the second known source of very high-energy neutrinos, the active nucleus of the galaxy M77 47M light-years away. To do this, it has accumulated data from the telescope's 10 years of operation, observing some 80 ultra-energetic neutrinos from this object. The task has not been easy, as neutrinos are highly elusive. To put this into perspective, about one neutrino from M77 passes through the detector per second, but only 80 have been captured in 10 years. 

IceCube has been trying to take a neutrino 'picture' of the Universe for all this time, but until now it has only managed to locate one other object, the blazar TXS 0506+056 (another supermassive black hole, much further away than M77). The difference is that on that occasion the detection was possible thanks to the collaboration of other telescopes around the world, which made it possible to capture a flare emitted by the object (one of the first examples of multimessenger detection). In this case, IceCube has been able to observe the continuous emission of neutrinos from M77 thanks to long exposure times and improved image analysis (thus improving the telescope's 'pointing'(*) capabilities), confirming indications published in 2020 that pointed to M77 as a possible source of neutrinos. It is also interesting to note that the black hole at the centre of M77 is obscured by the surrounding accretion disc, as we see this galaxy in profile and, therefore, its observation with other telescopes (visible-light, X-ray or gamma-ray) is more difficult. Neutrinos, on the other hand, are an ideal tool to 'see' through this disc. 

Thanks to this discovery, the possible origin of the highest energy cosmic rays, one of the most important open problems in astrophysics, is beginning to be identified. Cosmic rays are charged particles that reach enormous energies. It is not clear what phenomena can accelerate these rays to these energies, and it is difficult to identify the origin of these particles, since they are deflected by intergalactic magnetic fields on their journey to Earth. Possible candidates are active galaxy nuclei (AGNs), which, in addition to cosmic rays, are also expected to produce neutrinos, which would travel unchanged to us. The positive IceCube detection of M77 and three other somewhat less intense sources therefore clearly point to these objects as one of the important sources of ultra-energetic cosmic rays, confirming the models. 

These four sources account for a small percentage of all neutrinos detected by IceCube, which are so far of unknown origin. Further data accumulation will be needed to clarify whether AGNs are the only sources of high-energy cosmic rays, or whether new 'cosmic accelerators' are discovered. Indeed, given the different nature of the blazar TXS0506+056 and the AGN in M77, the collaboration suggests the existence of at least two different types of sources. Exciting times are ahead for multimessenger astronomy!

(*) The instrument has no moving parts: it reconstructs the direction of the incident particles from the light signals generated in the Antarctic ice, producing a much less sharp image, for example, than optical telescopes.