Rare triple quasar

Print edition : April 19, 2013

FOR only the second time in history, a team of scientists has discovered an extremely rare triple quasar system. Its work is published by Monthly Notices of the Royal Astronomical Society. Quasars are extremely bright and powerful sources of energy that sit in the centre of a galaxy, surrounding a black hole. In systems with multiple quasars, the bodies are held together by gravity and are believed to be the product of galaxies colliding. It is very difficult to observe triplet quasar systems because of observational limits that prevent researchers from differentiating multiple nearby bodies from one another at astronomical distances. Moreover, such phenomena are presumed to be very rare.

By combining multiple telescope observations and advanced modelling, the team —led by Emanuele Farina of the University of Insubria in Como, Italy—was able to find the triplet quasar. Advanced analysis confirmed that what the team found was indeed three distinct sources of quasar energy, two of which are closer to each other than the third. This means that the system could have been formed by interaction between these two but was probably not triggered by interaction with the more distant third quasar. Also, no evidence was seen of any ultra-luminous infrared galaxies, which is where quasars are commonly found. As a result, the team proposes that this triplet quasar system is part of some larger structure that is still undergoing formation. “Further study will help us figure out exactly how these quasars came to be and how rare their formation is,” said Michele Fumagalli, of the Carnegie Institution for Science,U.S., and a member of the team.