Scientists have unlocked one of the biggest mysteries of quasars — the brightest, most powerful objects in the Universe — discovering that they are ignited by galaxies colliding.

Quasars can shine as brightly as a trillion stars packed into a volume the size of our Solar System, but until now it has remained a mystery what could trigger such powerful activity,

Using deep imaging observations from the Isaac Newton Telescope in La Palma, Canary Islands, scientists at the universities of Sheffield and Hertfordshire observed 48 galaxies that host quasars and compared them to more than 100 non-quasar galaxies.

The future of our own Milky Way galaxy

When two galaxies collide, gravitational forces push huge amounts of gas towards supermassive black holes. The ignition of a quasar can have dramatic consequences for entire galaxies. 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. the centre of the remnant galaxy system that results from the collision. Just before the gas is consumed by the black hole, it releases extraordinary amounts of in the form of radiation, resulting in a quasar.

“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,” said Professor Clive Tadhunter, from the University of Sheffield’s Department of Physics and Astronomy.

Beacons to the history (and future) of the universe

“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,” said Dr. Jonny Pierce, Post-Doctoral Research Fellow at the University of Hertfordshire.

“It’s an area that scientists around the world are keen to learn more about. 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.”

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