Scientists 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.

  • Quasars, discovered 60 years ago, can shine as brilliantly as a trillion stars crammed into a volume the size of our Solar System, but what causes such intense activity is unknown.
  • Scientists found that galaxies colliding ignite the phenomena by observing 48 quasar-hosting galaxies and comparing them to over 100 non-quasar galaxies.
  • When two galaxies collide, gravitational forces push huge amounts of gas toward supermassive black holes at the center of the remnant galaxy system. Before the gas is consumed by the black hole, it releases radiation, creating a quasar.
  • In five billion years, the Milky Way will collide with the Andromeda galaxy, creating a quasar.

Quasars, discovered 60 years ago, can shine as brilliantly as a trillion stars crammed into our Solar System. What causes such tremendous activity has remained a mystery for decades. Scientists at Sheffield and Hertfordshire have found that galaxies colliding cause it.

The Isaac Newton Telescope in La Palma found deformed structures in the outer regions of quasar-hosting galaxies, indicating collisions.

Supermassive black holes center most galaxies. They contain lots of gas, but most of it orbits far from the galaxy centers, out of black hole reach. The quasar’s brilliance comes from gas colliding with galaxies and being sucked into the galaxy’s black hole.

Quasars can force gas out of galaxies, preventing them from creating new stars for billions of years.

This is the first time a sample of this size quasars has been photographed thus sensitively. Researchers found that quasar-hosting galaxies are three times more likely to interact with other galaxies by comparing photos of 48 quasars and their host galaxies to over 100 non-quasar galaxies.

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

The study improved our understanding of how these powerful objects are triggered and fueled.

“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.”

Astrophysicists use quasars as lighthouses to the Universe’s earliest epochs because of their brilliance. Dr. Jonny Pierce, University of Hertfordshire Post-Doctoral Research Fellow:

“It’s an area that scientists around the world are keen to learn more about – one of NASA’s James Webb Space Telescope’s main scientific motivations was to study the Universe’s earliest galaxies, and Webb can detect light from even the most distant quasars, emitted nearly 13 billion years ago. Quasars help us comprehend the Universe’s history and maybe the Milky Way’s future.

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