Mystery solved as scientists discover how quasars are made

Where do quasars – the brightest, most powerful objects in the universe – come from? British researchers have discovered that they are ignited by the collision of galaxies.

Quasars, or “quasi-stellar astronomical objects”, were first discovered in 1962. Since then, astrophysicists have wondered what could power these objects that somehow manage to pack the brightness of a trillion suns into a volume the size of our solar system.

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Researchers from the Universities of Sheffield and Hertfordshire used deep imaging observations from the Isaac Newton Telescope in La Palma on the Canary Islands to find the tell-tale signs of galactic mergers around quasars.

All galaxies have gas. And lots of it. A large portion of this gas lies out of the reach of the supermassive black holes that dwell in the centres of most galaxies.

But galactic collisions drive this gas towards the supermassive black holes where the gases eventually fall victim to the immense gravitational pull of the behemoth at the centre of the galaxy. Just before being consumed, the gas in the merging galaxies release extraordinary amounts of radiation. And voila, a quasar is born.

Distorted structures in the outer regions of galaxies that contain quasars suggest such a genesis.

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The astrophysicists compared 48 galaxies hosting quasars with more than 100 non-quasar galaxies. Their results show that galaxies with quasars are about three times as likely to be interacting or colliding with other galaxies.

“Quasars are one of the most extreme phenomena in the universe, and what we see is likely to represent the future of our own Milky Way galaxy when it collides with the Andromeda galaxy in about five billion years,” says the University of Sheffield’s Professor Clive Tadhunter. “It’s exciting to observe these events and finally understand why they occur – but thankfully Earth won’t be anywhere near one of these apocalyptic episodes for quite some time.”

“It’s an area that scientists around the world are keen to learn more about,” adds Dr Jonny Pierce from the University of Hertfordshire. “One of the main scientific motivations for NASA’s James Webb Space Telescope was to study the earliest galaxies in the universe, and Webb is capable of detecting light from even the most distant quasars, emitted nearly 13 billion years ago. Quasars play a key role in our understanding of the history of the universe, and possibly also the future of the Milky Way.”

The research is published in in the Monthly Notices of the Royal Astronomical Society.

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