Scientists have unraveled one of the biggest mysteries of quasars – the brightest and most powerful objects in the universe – by discovering that they are ignited by colliding galaxies.
First discovered 60 years ago, quasars can shine as brightly as a trillion stars packed in a volume the size of our solar system. In the decades since they were first observed, what could trigger such intense activity has remained a mystery. New work led by scientists from the Universities of Sheffield and Hertfordshire has now shown that this is a result of galaxy collisions.
The collisions were discovered when researchers, using deep imaging observations from the Isaac Newton Telescope on La Palma, observed the presence of distorted structures in the outer regions of galaxies that are home to quasars.
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Most galaxies have supermassive black holes at their centers. They also contain significant amounts of gas – but for the most part this gas orbits far away from the galaxy’s centers, beyond the reach of the black holes.
Collisions between galaxies push the gas towards the black hole at the center of the galaxy; Just before the gas is consumed by the black hole, it releases extraordinary amounts of energy in the form of radiation, resulting in the quasar’s characteristic brilliance.
The ignition of a quasar can have dramatic consequences for entire galaxies – it can force the rest of the gas out of the galaxy, preventing it from forming new stars for billions of years.
This is the first time a sample of quasars of this size has been imaged with this sensitivity. By comparing observations of 48 quasars and their host galaxies with images of over 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, published this week in Monthly Bulletins of the Royal Astronomical Society has greatly advanced our understanding of how these powerful objects are triggered and powered.
Professor Clive Tadhunter, from the University of Sheffield’s Faculty of Physics and Astronomy, said: “Quasars are one of the most extreme phenomena in the Universe, and what we are seeing likely represents the future of our own Milky Way when it collides with the Andromeda Galaxy in about five billion years.
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“It’s exciting to watch these events and finally understand why they’re occurring — but fortunately, Earth won’t be anywhere near any of these apocalyptic episodes for quite a while.”
Quasars are important to astrophysicists because their brightness makes them noticeable at great distances, thus acting as beacons into the earliest epochs of the history of the universe. dr Jonny Pierce, Postdoctoral Research Fellow at the University of Hertfordshire explains:
“It’s an area that scientists around the world would like to learn more about — one of the key scientific motivations for NASA’s James Webb Space Telescope was to study the earliest galaxies in the universe, and Webb is capable of observing light himself.” the most distant to spot quasars emitted almost 13 billion years ago.
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“Quasars play a key role in our understanding of the history of the Universe and possibly the future of the Milky Way.”
(Source: University of Sheffield)
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