New research reveals that supermassive black holes at the core of galaxies, known as quasars, can sometimes be obscured by dense clouds of gas and dust in their host galaxies.
This challenges the prevailing view that quasars are only hidden by donut-shaped rings of dust in the vicinity of the black hole.
Quasars are extremely luminous objects that are powered by black holes collapsing from the surrounding matter. Its powerful radiation can be blocked if dense clouds come between us and the quasar.
Astronomers have long thought that this hidden object exists only in the immediate vicinity of the quasar, in the “dusty torus” (or doughnut) that surrounds it.
Now, a team of scientists led by Durham University has found evidence that in some quasars, the total dimming is caused by the host galaxy.
Using the Atacama Large Millimeter Array (ALMA) in Chile, they observed a sample of very dusty quasars with strong rates of star formation.
They found that many of these quasars reside in much smaller galaxies, known as “stellar stars,” no more than 3000 light-years away.
These starburst galaxies can form more than 1000 sun-like stars per year.
To form such a large number of stars, a galaxy needs a large amount of gas and dust, which are the basic building blocks of stars. In such galaxies, clouds of gas and dust stirred up by rapid star formation can accumulate and completely obscure the quasar.
The full study is published in the journal Monthly notices of the Royal Astronomical Society (MNRAS). Lead study author Carolina Andonie, Ph.D. student at the Center for Extragalactic Astronomy at Durham University, said, “It’s like a quasar is buried in its own galaxy.
In some cases, the surrounding galaxy is so full of gas and dust that even X-rays cannot escape.
“We always thought that the dusty donut around the black hole was the only thing hiding the quasar from view.
“Now we see that the whole galaxy can participate.
“This phenomenon seems to only happen when the quasar is growing in power.”
The team estimates that in about 10–30% of quasars that form stars very quickly, the host galaxy is responsible for obscuring the quasar.
The findings provide new insights into the connection between galaxy growth and black hole activity.
Unseen quasars may represent an early stage of evolution, when young galaxies are rich in cold gas and dust, fueling high rates of star formation and the growth of black holes.
Co-author of the study Professor David Alexander of Durham University said, “It’s a turbulent, chaotic phase of evolution, where gas and stars collide and merge at the center of the galaxy. The cosmic food fight shrouds the baby quasar in its dust.”
Uncovering these buried quasars will help scientists understand the connection between galaxies and the supermassive black holes at their hearts.
Carolina Andonie et al, Fading beyond the nucleus: infrared quasars can be buried by bright starbursts, MNRAS (2023). Opened arXiv: DOI: 10.48550/arxiv.2310.02330
Provided by Durham University
An excerpt: New study shows that quasars can be buried in their own galaxies (2023, November 5) downloaded on 6 November 2023 from https://phys.org/news/2023-11-quasars-host-galaxies.html
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