Science & Technology

Galaxy mergers ignite ‘quasars’ — the most powerful celestial objects: Study

Quasars likely to be future of Milky Way galaxy when it collides with Andromeda in about 5 billion years

By Rohini Krishnamurthy
Published: Wednesday 26 April 2023
An artist’s rendering of quasar P172+18. Photo: ESO-M Kornmesse.
An artist’s rendering of quasar P172+18. Photo: ESO-M Kornmesse. An artist’s rendering of quasar P172+18. Photo: ESO-M Kornmesse.

Quasars — the brightest and the most powerful objects in the universe — have a violent origin story, according to a new study. The celestial bodies shine as brightly as a trillion stars, but are a fraction of the size, concentrated in a region as small as our Solar System. 

The collision of two galaxies likely ignites quasars, the new study published in journal Monthly Notices of the Royal Astronomical Society highlighted. 

Read more: Most distant source of radio emission discovered, holds clues about ancient universe

Quasars, short for “quasi-stellar radio sources”, were first discovered six decades ago. They are located in supermassive black holes, which sit in the centre of galaxies.

As a supermassive black hole feed on gas and dust, it releases extraordinary amounts of energy in the form of radiation, resulting in a quasar.

The mechanisms that trigger quasars have been hotly debated. Some studies suggest galaxy mergers are responsible, while others found little evidence to support the theory.

“We believe that this [mixed results] is because the images used in many studies were not sensitive enough to detect them. To tackle this issue, we decided to image a large sample of quasars with the appropriate depth to identify these signatures,” Jonny Pierce, post-doctoral research fellow at the University of Hertfordshire, told Down To Earth.

To do this, researchers from the University of Sheffield and Hertfordshire relied on the Isaac Newton Telescope in La Palma in the Canary Islands. They compared 48 galaxies that host quasars with over 100 non-quasar galaxies.

Galaxies that host a quasar showed morphological features that are consistent with galaxy mergers, the researchers noted.

Read more: Scientists capture first image of supermassive black hole in Milky Way and it is starving

When galaxies collide, it pushes the gas from the outer reaches of the galaxies to the centre. And as the supermassive black hole gorges on the gas, it releases ferocious fountains of energy in the form of radiation, leading to the quasar.

These results present strong evidence that galaxy interactions are the dominant trigger for quasars in the local universe. However, they are unlikely to be the sole factor, the researchers wrote in their study.

Significance of quasars

When a quasar is ignited, it can drive the rest of the gas out of the galaxy. “The radiation from these objects is so intense that intervening gas within the galaxy feels a pressure that moves it away from the quasar in the nucleus, driving “outflows” of material,” Pierce explained.

In extreme cases, he added, a significant fraction of the total gas in a galaxy gets displaced. This has drastic consequences on star formation. Also, the collision of the Milky Way galaxy with the Andromeda galaxy could likely trigger a quasar, the scientists predict in their study.

“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,” Clive Tadhunter, from the University of Sheffield’s department of physics and astronomy, said in a statement.

Read more: Astronomers detect biggest collision of ‘impossible’ black holes

“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,” he added.

Further, quasars act as “cosmic lighthouses”, allowing researchers to see the outer reaches of the universe.

NASA’s James Webb Space Telescope will study the earliest galaxies in the universe. The telescope, Pierce said, is capable of detecting light from even the most distant quasars, emitted nearly 13 billion years ago. 

“Now that we know that galaxy collisions are very important for triggering this activity in galaxies closer to us, we can consider whether these events were also important for igniting quasars in earlier epochs of the universe,” Pierce explained.

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