Scientists have solved 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 trillions of stars packed into the size of our solar system. In the decades since they were first observed, what could cause such powerful activity remains a mystery. The new work, led by scientists from the Universities of Sheffield and Hertfordshire, has now revealed that this is the result of colliding galaxies.
The collisions were discovered when researchers, using deep imaging observations from the Isaac Newton Telescope at La Palma, observed the presence of distorted structures in the outer regions of galaxies that host quasars.
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Most galaxies have supermassive black holes at their centers. They also contain significant amounts of gas, but most of the time 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; just before the gas is consumed by the black hole, it emits an enormous amount of energy in the form of radiation, resulting in the characteristic glow of a quasar.
A quasar’s flare-up can have dramatic consequences for entire galaxies — it can push the rest of the gas out of 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 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.
A study published this week Monthly Notices of the Royal Astronomical Society has provided a significant step forward in our understanding of how these powerful objects are activated and powered.
Professor Clive Tadhunter, from 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 are seeing is likely to reflect the future of our own Milky Way galaxy as it collides with the Andromeda galaxy in about five billion years’ time.
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“It’s exciting to observe these events and finally understand why they happen, but thankfully Earth won’t be anywhere near any of these apocalyptic episodes for some time to come.”
Quasars are important to astrophysicists because their brightness makes them stand out at great distances and therefore act as beacons for the earliest epochs of the universe’s history. Dr Jonny Pierce, a postdoctoral researcher at the University of Hertfordshire, explains:
“This is an area that scientists around the world want to know more about – one of the main scientific motivations for NASA’s James Webb Space Telescope was to study the oldest galaxies in the universe, and Webb is able to detect light from even the most distant galaxies. Quasars emitted nearly 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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