The spark that set the cosmos on fire

British scientists have unlocked the secrets of quasars, the universe's most violently energetic objects.

Researchers led by Dr James Dunlop, of Edinburgh University, have pinpointed a class of galaxies, known as elliptical galaxies, as the sources of these intensely powerful beams of radiation.

The discovery is a personal triumph for Dunlop, who was given unprecedented access to the Hubble space telescope, using the robot spaceship for more than 100 hours.

'A quasar is so bright and violent it outshines all the other millions of stars that make up its galaxy. They dazzle us, in effect,' said Dunlop, who is based at the Royal Observatory in Edinburgh.

'However, Hubble has such fantastic resolution that we have been able to determine the nature of quasars' host galaxies for the first time. And that has provided us with the key to understanding their structure and behaviour.'

Quasars were discovered in the Sixties, when they were assumed to be nearby stars because their radiation was so bright and intense.

Subsequent observations revealed, however, that they were the most distant objects known to mankind, and lay at the other end of the universe.

Therefore, it was realised that only objects of incredible energy could be responsible for their output - and that suggested the involvement of black holes.

Black holes are super-heavy, collapsed giant stars whose gravity is so powerful not even light can escape their surfaces. Matter sucked into them would emit blasts of radiation, a mechanism that would explain quasars' energetic emissions.

'It would be like pouring paraffin over a glowing ember. It would make them burst into flames,' Dunlop said.

Proving this idea was a different matter. Quasars blinded astronomers with their cosmic brilliance and obscured their vision, blazing so fiercely, and so long ago - billions of years in the past - that scientists faced a second headache: what happened to quasars? The universe today contains no hint of one, which is perhaps just as well, given the violence of their outpourings.

Dunlop's discoveries now provide some answers. Elliptical galaxies exist in the modern universe, and the largest ones are known to have giant black holes - the mass of a billion stars - at their cores.

'They are quiet now, but in the early universe, when there was gas everywhere, they would have been sucking in matter like cosmic vacuum cleaners,' he said. 'That turned them into quasars.'

Having used up all their gassy fuel, quasars in these galaxies then died down. 'But if gas were to start pouring back in for some reason, they would burst into life again.'

Black holes probably exist at the heart of all galaxies, but those in smaller, elliptical galaxies simply lacked the gravitas to pull in enough gas and erupt as quasars.

Instead, many of these smaller galaxies went through a different - and very important - evolutionary process. They developed spiral arms.

It was in the middle one of these arms, in a small undistinguished spiral galaxy, that our own sun - an unremarkable star - was born five billion years ago. And around this star, our own planet evolved - far from the madding heart of the rest of a frenzied cosmos.

• Space
• The Observer
• Astronomy
• Black holes

ncG1vNJzZmivp6x7tbTEoKyaqpSerq96wqikaKuTnrKvr8RoaHJxaWS6osWOam1oq6CWsKax16mjqKqRqbawuo2upaKulafApg%3D%3D