A single neutrino was detected on September 2017 in Antarctica by a neutrino detector. It was the first high energy neutrino which was traced back to a blazar galaxy named TXS 0506+056 at a distance of 3.8 billion light-years from us. However, it raised the question of why only this galaxy was the neutrino traced back to?
Researchers might have obtained the answer. The relativistic jet from the supermassive black hole might have acted as a cosmic particle collider resulting in neutrinos that streamed through Earth due to the jet’s shape. Hence this indicates that a binary supermassive black hole is present at TXS 0506+056’s centre, the end result of the merger of two galaxies. The findings appear in the Astronomy & Astrophysics journal.
Neutrinos are one of the most abundant subatomic particles in the Universe. They are not charged, nearly massless and do not interact with any object. As a result they are quite hard to detect. They interacted with the ice present below the surface of Antarctica producing a shower of particles, which produced the Cherenkov radiation observed by the Cherenkov detectors at IceCube Neutrino Observatory.
Tracking a neutrino is another challenging task and it took a multi-messenger astronomy to achieve it. As a result, we now know that this neutrino named IceCube-170922A originated from a blazar. So we might conclude that only blazars are the only source for the neutrinos. But TXS 0506+056 is the only blazar traced back for the neutrinos. Hence an international group of researchers led by Silke Britzen, Max Planck Institute for Radio Astronomy, Germany started to find the reason. Britzen said that they wanted to know the reason for TXS 0506+056 being so special, understand the creation process of neutrinos and localise the site of emission, studying through radio images of high resolution.
A series of observations by the Very Long Baseline Array between 2009 and 2018 were reanalysed by the team studying the kinematics of the jet along with the flux-density evolution of individual jet components. Special attention was given to the period of 2014 and 2015 where high neutrino activity was detected.
Jet dynamics were not found to be smooth and undisturbed as predicted, however some jet parts were colliding with other parts. It might be the result of new jet colliding with old jet or jets from different sources or clashing of jets from the same source. Flaring flux density was identified in six jet parts near the collision site, supporting the hypothesis.
Markus Bottcher, Northwest University, South Africa said that the neutrino detection can only be explained by the collision of the jetted material. Besides providing important insights, it solves the question if jets are leptonic, consisting of electrons, positrons or hadronic, having both electrons and protons. Some of the jet has to be hadronic for the neutrino to be detected.
The jet was also found to be curved and the black hole wobbling leading to the precession of the jet similar to a wobbling top. There might be a second black hole producing a second jet. Christian Fendt, astronomer at Max Planck Institute for Astronomy said that deeper analysis of the jet sources results in new complicated understanding of the jet dynamics and internal structures. The existence of binary black holes is due to the formation of galaxies by galaxy mergers.
Journal Reference: Astronomy & Astrophysics