Thursday, August 8, 2019

True Colors of Evolving Galactic Beasts Revealed

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

Now Durham University’s researchers have found a phase in the development of these galactic giants that could tell us more about how quasars and their host galaxies evolve.
Blue quasars

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.

Red quasars

Our 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.

A brief transitional phase where the young quasar is enshrouded in gas and dust. This phase is potentially associated with young jets and strong winds, which ultimately drive away the obscuring dust.

Credit: S. Munro.

This injection of energy blows away the dust and gas to reveal a blue quasar.

Our astronomers 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.
Galaxy evolution

They say their research could also tell us more about galaxy evolution as they expect that the massive burst of energy from the black hole would burn off the gas needed to form stars.

An unobscured quasar with signatures of evolved jets and less extreme winds that ultimately shut down star formation

Credit: S. Munro.

Without gas, the galaxies can’t grow – so the quasar is effectively ending the life of the galaxy by destroying the very thing that it needs to survive.
Find out more

The research was led by PhD researcher Lizelke Klindt and Professor David Alexander in our Centre for Extragalactic Astronomy.

It was published in Monthly Notices of the Royal Astronomical Society

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

Contacts and sources:
Angela Gemmill
Durham University

Citation: Fundamental differences in the radio properties of red and blue quasars: evolution strongly favoured over orientation L Klindt, D M Alexander, D J Rosario, E Lusso, S Fotopoulou Monthly Notices of the Royal Astronomical Society, Volume 488, Issue 3, September 2019, Pages 3109–3128,

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