The international scientific collaboration Event Horizon Telescope (EHT), which also includes a group of researchers from the University of Trieste, has observed and studied at different wavelengths a spectacular flare from the powerful relativistic jet of the supermassive black hole at the centre of the galaxy Messier 87 (M87*), the subject of the first ‘photo’ of a black hole. The study, coordinated by the EHT-MWL group and in collaboration with institutions such as INAF (Italian national institute of astrophysics), INFN (Italian national institute of nuclear physics) and ASI (Italian space association), has been accepted for publication in the prestigious journal Astronomy & Astrophysics. 

The event was documented during EHT's second observation mission in April 2018, involving more than 25 ground- and space-based telescopes and collecting data at different wavelengths. For the first time since 2010, a gamma-ray burst at very high energies, up to trillions of electron volts, was detected, lasting about three days. ‘We were fortunate to detect a gamma-ray burst from M87* during the Event Horizon Telescope's multi-wavelength mission. The observations will provide us with further insights and an incredible opportunity to investigate the physics around the supermassive black hole M87*, explaining the connection between the accretion disk and the emitted jet, as well as the origin and mechanisms responsible for the emission of gamma-ray photons,’ comments Giacomo Principe, lead author of the paper, UniTS researcher and INAF and INFN associate. 

The relativistic jet, extending over dimensions that exceed millions of times those of the black hole's event horizon, has been observed with leading telescopes such as Fermi-LAT, MAGIC and HESS. Francesco Longo, head of the Gamma Astrophysics group for the University and INFN of Trieste, says: ‘Observations made simultaneously at different wavelengths are fundamental for contemporary astrophysics. The availability of an instrument like Fermi-LAT, capable of continuously monitoring the sky in the gamma band, is crucial for detecting rare phenomena, such as the gamma flare from M87. In addition, ground-based gamma-ray instruments, capable of observing the sky at higher energies, allow the emission mechanism of gamma-ray sources to be studied with greater sensitivity'.

The data published in the paper also show a significant variation in the position angle of the ring asymmetry (the so-called ‘event horizon’ of the black hole), helping to solve scientific questions such as the origin of cosmic rays and the formation of relativistic jets. Principe concludes: ‘These observations may shed light on some major astrophysical questions that are still unresolved: how do the powerful relativistic jets observed in some galaxies originate? Where are the particles responsible for gamma-ray emission accelerated? What phenomenon accelerates them to energies of TeV (trillions of electron volts)? What is the origin of cosmic rays?’ 

The full study is available here : “Broadband Multi-wavelength Properties of M87 during the 2018 EHT Campaign including a Very High Energy Flaring Episode”