Astronomers solve 60-year mystery of quasars, the most powerful objects in the universe

Scientists have unlocked one of the biggest mysteries of quasars – the brightest, most powerful objects in the universe – discovering that they burn galaxies as they collide.

First discovered 60 years ago, quasars can shine like trillions of stars packed into a mass the size of our solar system. In the decades since they were first observed, what could trigger such powerful activity has remained a mystery. New work led by scientists from the Universities of Sheffield and Hertfordshire has now revealed that they are the result of galaxies collapsing together.

Published in the work Monthly Notices of the Royal Astronomical Society.

The collision was 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 galaxies that are home to quasars.

Most galaxies have supermassive black holes at their centers. It also contains significant amounts of gas—but most of this gas orbits at great distances from the galactic centers, beyond the reach of black holes. Collisions between galaxies drive gas toward the black hole at the center of the galaxy; Before the gas is consumed by the black hole, it releases an extraordinary amount 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—it can expel the remaining gas from the galaxy, preventing 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. By comparing observations of 48 quasars and their host galaxies with images of more than 100 non-quasar galaxies, the researchers concluded that galaxies hosting quasars are about three times more likely to interact or collide with other galaxies.

The study provided an important step forward in our understanding of how these powerful substances are triggered and fueled.

“Quasars are one of the most extreme events in the universe, and what we see represents the future of our own galaxy when it collides with the Andromeda galaxy in about five billion years,” said Professor Clive Tadhunter, from the Department of Physics and Astronomy at the University of Sheffield.

“It’s exciting to observe these events and finally understand why they happen – but fortunately Earth won’t be near one of these apocalyptic episodes for a while.”

Quasars are important to astrophysicists because, due to their luminosity, they stand out at great distances and therefore act as beacons for the earliest epochs in the history of the universe.

Dr. Jonny Pearce, a post-doctoral research fellow at the University of Hertfordshire, explains, “It’s an area that scientists around the world are keen to learn more about – one of the main scientific inspirations for NASA’s James Webb Space Telescope. The oldest galaxies in the universe, and the Webb able to detect light from even the most distant quasars, emitted about 13 billion years ago. Quasars play an important role in our understanding of the history of the universe and possibly the future of the Milky Way.”