The farthest black hole ever caught feasting has been identified: it is 8.5 billion light-years from us and, in the heat of devouring its stellar meal, it has emitted an unusual jet of radiation directed towards the Earth.
The signal, identified in February thanks to the Zwicky Transient Facility (ZTF) telescope in the United States, was then studied until its source was revealed thanks to the Very Large Telescope (VLT) of the European Southern Observatory (ESO) in Chile. The discovery is described in two articles published respectively in the journals Nature Astronomy and Nature: the latter bears as its first signature that of the astrophysicist Igor Andreoni, born in Milan and raised in Bergamo and today at the University of Maryland.
Artist's impression of a black hole devouring a star (source: ESO/M.Kornmesser)
"We have developed an open source data analysis system to archive and extract important information from the observations made with ZTF - explains Andreoni - in order to be notified in real time when an atypical event occurs".
The alert was triggered last February, when ZTF detected a new source of visible light.
The event, dubbed AT2022cmc, resembled a burst of gamma rays, the most powerful light source in the Universe.
The prospect of witnessing this rare phenomenon has prompted astronomers to activate several telescopes around the world to observe the unknown source in more detail.
Among these also the ESO VLT, which quickly observed the new event with the X-shooter instrument.
A wide variety of radiation, from high-energy gamma rays to radio waves, was collected by 21 telescopes around the world.
The researchers compared this data to different types of known events, from collapsing stars to kilonovae: the only scenario that could explain the data was a rare cosmic 'feast' in which a star is torn apart by the incredible force of attraction gravity of the black hole.
About 1% of these events result in jets of plasma and radiation being ejected from the poles of the spinning black hole, like a tube of toothpaste squeezed in the middle spraying material from both ends.
In this case, since the jet was aimed at the Earth,