Quasars are extremely bright objects with massive black holes at their centres. Usually, quasars are obscured by donut-shaped rings of dust surrounding them.
But now, scientists from our world-leading Centre for Extragalactic Astronomy in the Physics department have found that quasars can also be obscured by the gas and dust in their entire host galaxies.
Using the Atacama Large Millimeter Array (ALMA) in Chile, the researchers observed a sample of very dusty quasars that were forming stars rapidly.
They found that many of these quasars live in very compact galaxies, known as “starburst galaxies”, only a few thousand light-years across.
These starburst galaxies can form more than 1,000 stars like the Sun per year.
To form such a large number of stars, the galaxy needs huge amounts of gas and dust, which are essentially the building blocks of stars.
In such galaxies, clouds of dust and gas stirred up by star formation can completely surround the quasar and block its light.
The study estimates that in about 10-30 per cent of very rapidly star-forming quasars, the host galaxy itself hides the quasar from view.
This only seems to happen when the quasar is growing intensely.
The results give new insights into how galaxies and their central black holes co-evolve.
Hidden quasars represent an early, messy stage of growth, when galaxies are rich in gas and dust.
Unveiling these buried quasars will help scientists understand the link between galaxies and supermassive black holes.
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