If black holes are objects of enormous fascination, quasars are perhaps even more so, even for astronomers. Observed for the first time in the early 1960s, those considered to be among the brightest objects in the Universe have in fact kept their origins a secret for about sixty years: today we know more thanks to an article published in the journal Monthly Notices of the Royal Astronomical Society. The study, led by Jonny Pierce of the University of Hertfordshire (UK), shows us in fact that their “ignition” is linked to the collision between two galaxies.
The name quasar derives from the way they were initially described, i.e. as astronomical objects similar to stars and capable of emitting radio waves – “quasi stellar radio source”. These are extra-galactic astronomical objects, which are located at enormous distances from us, and our instruments have been able to detect their presence due to the enormous amount of energy they emit starting from their nucleus. To study their mysterious origins, the research team observed 48 galaxies that host quasars inside them and compared them with images of over 100 galaxies that do not contain them. Their analyzes showed that the former are about three times more likely to collide or interact with other galaxies than the latter. According to the authors, it would be precisely these collisions between galaxies that favor the movement of the large quantities of gas contained in them towards the supermassive black holes that often lie at their centre. The gas is thus consumed by the black hole, a phenomenon that we know causes the release of enormous quantities of energy in the form of electromagnetic radiation: this explains the origin of the characteristic luminosity of the quasar.
Why Study Quasars
“Quasars – explains Clive Tadhunter of the University of Sheffield (United Kingdom), second author of the article – are one of the most extreme phenomena in the Universe, and what we see most likely represents the future of our Milky Way when it collides with the Andromeda galaxy in about five billion years”. The birth of a quasar can cause the gas contained in the galaxies from which it originated to run out, which can have dramatic consequences for the galaxies themselves, such as the inability to form new stars for billions of years. But not only. We are also interested in quasars because they are a sort of “window on the past of the Universe” precisely because they are visible, thanks to the enormous amount of energy they emit, even from great distances. “It is an area – concludes Jonny Pierce of the University of Hertfordshire, who led the study – that scientists from all over the world are inclined to know better and better: one of the main scientific motivations of NASA’s James Webb Space Telescope was to study the first galaxies of the Universe, and Webb is able to detect the light of even the most distant quasars, emitted almost 13 billion years ago. Quasars play a fundamental role in understanding the history of the Universe and perhaps also the future of the Milky Way.”