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UK astronomy team reveal quasars' true colours

7 August 2019

Astronomers have identified a rare moment in the life of some of the universe’s most energetic objects.

Quasars were first observed 60 years ago, but their origins still remain a mystery. Now researchers at Durham University, co-funded by STFC, have spotted what they suggest is a “brief transition phase” in the development of these galactic giants that could shed light on how quasars and their host galaxies evolve.

Quasars are powered by supermassive black holes at their centres and most appear blue in colour.

However, a significant number of quasars look red when viewed through the huge clouds of dust and gas that obscure them from view.

The conventional view of red quasars is that they are actually blue quasars that are angled away from our line-of-sight.

However, the Durham team has ruled out this model and instead has shown that red quasars are likely to be the result of a brief, but violent, phase in the evolution of galaxies when their black holes are ejecting large amounts of energy into the surrounding dust and gas.

Lead author Lizelke Klindt, a PhD researcher in Durham University’s Centre for Extragalactic Astronomy, said: “How quasars develop has been the cause of significant uncertainty. What our results suggest is that quasars undergo a brief transition phase, changing colour from red to blue, when they emerge from the deep shroud of dust and gas surrounding them.”

The researchers studied 10,000 red and blue quasars as they would have been seen seven to 11 billion years ago when the universe was relatively young using archival data from the Sloan Digital Sky Survey and the Very Large Array radio astronomy observatory.

The researchers say the next step in their research is to use more in-depth data to understand the finer details of this transition phase.

Notes for editors

It was published in Monthly Notices of the Royal Astronomical Society.

The research was funded by a Faculty of Science Durham Doctoral Scholarship, the Science and Technology Facilities Council, a European Union COFUND/Durham Junior Research Fellowship and the Swiss National Science Foundation.

Last updated: 08 August 2019


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