Scientists from the University of Hertfordshire have unlocked one of the biggest mysteries of quasars - the brightest, most powerful objects in the universe – by discovering that they are ignited by galaxies colliding. 

First discovered 60 years ago, quasars can shine as brightly as a trillion stars packed into a volume the size of our solar system. 

In the decades since they were first observed, one of the biggest mysteries puzzling experts has been what could trigger such powerful activity. 

New work, led by astrophysicists at the universities of Hertfordshire and Sheffield, has revealed that they are the consequence of galaxies crashing together. 

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Dr Jonny Pierce, post-doctoral research fellow at the University of Hertfordshire, said: "It’s an area that scientists around the world are keen to learn more about. 

"Quasars play a key role in our understanding of the history of the Universe, and possibly also the future of the Milky Way.” 

The collisions were discovered when researchers, using deep imaging observations from the Isaac Newton Telescope in La Palma, observed the presence of distorted structures in the outer regions of the galaxies that are home to quasars. 

Most galaxies have supermassive black holes at their centres, lurking in the nuclei. 

Collisions between galaxies drive prodigious amounts of gas towards the black hole at the galaxy centre. Just before the gas is consumed by the black hole, it releases enormous amounts of energy in the form of radiation, resulting in the characteristic quasar brilliance. 

The ignition of a quasar can have dramatic consequences for entire galaxies, and it can drive the rest of the gas out of the galaxy, which prevents it from forming new stars for billions of years into the future. 

This is the first time that a sample of quasars of this size has been imaged with this level of sensitivity. 

                                                                                                         

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Researchers concluded that galaxies hosting quasars are approximately three times as likely to be interacting or colliding with other galaxies. 

Quasars are important to astrophysicists because, due to their brightness, they stand out at large distances and therefore act as beacons to the earliest epochs in the history of the Universe.