Scientists have revealed 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 bright as a trillion stars packed into the volume of our solar system. In the decades since they were first observed, what could lead to such vigorous activity has remained a mystery. New work led by scientists at the Universities of Sheffield and Hertfordshire has now shown that it is a result of galaxies crashing together.
The work was published in Monthly Notices of the Royal Astronomical Society.
The collisions were discovered when researchers, using depth imaging observations from the Isaac Newton Telescope in La Palma, noticed distorted structures in the outer regions of galaxies that are home to quasars.
Most galaxies contain supermassive black holes at their centers. They also contain large amounts of gas – but most of the time this gas orbits at great distances from the centers of galaxies, out of reach of black holes. Collisions between galaxies push gas toward the black hole at the center of the galaxy. Just before the black hole consumes the gas, it releases extraordinary amounts of energy in the form of radiation, producing the quasar’s distinctive brilliance.
A quasar flare-up can have disastrous consequences for entire galaxies – it can eject remaining gas from the galaxy, preventing it from forming new stars billions of years into the future.
This is the first time a quasar sample 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 quasar host galaxies are about three times as likely to interact or collide with other galaxies.
The study provided an important step forward in our understanding of how these powerful objects are powered and powered.
Professor Cliff 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 see likely represents the future of our Milky Way when it collides with the Andromeda galaxy in about five billion years.
“It’s exciting to observe these events and finally understand why they happened – but fortunately Earth won’t be anywhere near one of these apocalyptic events for some time.”
Quasars are important to astrophysicists because they stand out at great distances due to their brightness, and thus serve as beacons for the earliest epochs in the history of the universe.
Dr Johnny Pearce, Postdoctoral 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 science drives for NASA’s James Webb Space Telescope was to study the oldest galaxies in the universe, and Webb is able to discover Light even from the most distant quasars, emitted nearly 13 billion years ago. Quasars play a major role in our understanding of the history of the universe, and possibly also the future of the Milky Way.”
JCS Pierce et al, Galaxy interactions are the dominant driver of local type 2 quasars, Monthly Notices of the Royal Astronomical Society (2023). DOI: 10.1093/mnras/stad455
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