15 September 2010
Galactic collisions fuel the most powerful objects in the Universe
A new study by researchers at the University of Sheffield suggests that cosmic collisions provide the fuel for quasars, which are among the most powerful objects in the Universe.
The two-year study, led by Dr Cristina Ramos Almeida and Professor Clive Tadhunter, from the University of Sheffield´s Department of Physics and Astronomy, aimed to explain why quasars appear so bright.
Quasars are found at the centres of galaxies, and generate a power equivalent to trillions of suns from a space smaller than our Solar System.
It is thought that quasars occur when supermassive black holes at the centres of galaxies accrete gas from their surroundings.
Yet, as supermassive black holes are known to exist in the centres of most galaxies, including our own, it has been a mystery as to why, and how, some generate extraordinary power in the form of quasars, but most do not.
A subset of quasars eject exquisite jets of particles moving at close to the speed of light that are like the cosmic equivalents of water spouts or geysers. Since these jets emit most of their radiation at the wavelengths used for radio communication on Earth, the galaxies hosting such quasars are known as radio galaxies.
The researchers used the eight metre Gemini South Telescope high in the Andes, Chile, to obtain images of a large sample of radio galaxies.
The images show that 85% of these radio galaxies have peculiar features including tails, bridges, dust lanes, multiple nuclei (galactic centers) and shells. Such features are characteristic of mergers or close encounters between galaxies. However, they are found in only 10% of "normal" inactive galaxies observed with the same sensitivity.
According to Dr Cristina Ramos Almeida: "Our new images, obtained with one of the world´s largest optical telescopes, probe deeper than past studies, revealing faint features that were missed in previous investigations."
These findings suggest that galactic collisions, which force the gas into nuclear regions of the interacting galaxies, cause the extreme powers of quasars.
Professor Clive Tadhunter, who was the team leader for the research, said: "It has long been suspected that extraordinary events are required to generate the immense powers associated with quasars.
"Whereas the super-massive black holes at the centres of most galaxies appear to be on a severe diet in terms of the amount of gas they consume, those in quasars are enjoying a feast.
"The detection of the rare signs of cosmic collisions in the overwhelming majority of radio galaxies suggests that quasars are fuelled by the gas flows associated with such collisions."
"Since cosmic collisions are one of the main ways in which galaxies grow and evolve, quasars are likely to mark the sites of particularly rapid evolution of galaxies."
Notes for Editors: The study is being published in an article titled `The optical morphologies of the 2Jy sample of radio galaxies: evidence for galaxy interactions´: C. Ramos Almeida et al., in the Monthly Notices of the Royal Astronomical Society (MNRAS). Funding for the research was provided by the UK Science and Technology Research Council (STFC).
The team is composed of Dr Cristina Ramos Almeida and Professor Clive Tadhunter (University of Sheffield, UK), Katherine Inskip (MPIA Heidelberg, Germany), Raffaella Morganti (Netherlands Institute for Radio Astronomy, the Netherlands), Joana Holt (Leiden Observatory, the Netherlands)and Dan Dicken (Rochester Institute of Technology, USA).
The study is based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (USA), the Science and Technology Facilities Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).
For further information please contact: Kyle Christie, Media Relations Assistant, on 0114 2229852 or email k.christie@sheffield.ac.uk
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