2023-11-06 11:48:59
Artist’s illustration of the thick torus of dust believed to surround supermassive black holes and their accretion disks. -DURHAM UNIVERSITY
MADRID, 6 Nov. (EUROPA PRESS) –
Quasars, extremely bright objects powered by supermassive black holes, can sometimes be obscured by dense clouds of gas and dust of their host galaxies.
This finding published in the journal ‘Monthly Notices of the Royal Astronomical Society’ challenges the prevailing idea that quasars They are only hidden by donut-shaped rings of dust in the vicinity of the black hole.
Quasars are extremely bright objects powered by black holes that devour surrounding material. Its powerful radiation can be blocked if thick clouds come between us and the quasar.
Astronomers have long thought that this obscuring material only exists in the quasar’s immediate environment, in a ‘dusty ring’ (or donut) surrounding it. Now, a team of scientists led by Durham University in the United Kingdom has found evidence that, in some quasars, the dimming is caused entirely by the host galaxy in which the quasar resides.
Using the Atacama Large Millimeter Array (ALMA) in Chile, they looked at a sample of very dusty quasars with intense star formation rates and found that many of these quasars live in very compact galaxies, known as “starburst galaxies.” no more than 3,000 light years in diameter.
These starburst galaxies can form more than 1,000 Sun-like stars per year. To form such a large number of stars, the galaxy needs an enormous amount of gas and dust, which are essentially the building blocks of stars.
In these types of galaxies, clouds of gas and dust kicked up by rapid star formation can clump together and completely obscure the quasar.
The lead author of the study, Carolina Andonie, a PhD student at the Center for Extragalactic Astronomy at Durham University, explains: “It is as if the quasar is buried in its host galaxy. In some cases, the surrounding galaxy is so full of gas and dust that not even X-rays can escape.”
“We had always thought that the only thing hiding the quasar was the dust surrounding the black hole,” he points out. “Now we realize that the entire galaxy can participate. “This phenomenon only seems to occur when the quasar experiences intense growth.”
The team estimates that in about 10-30% of very rapid star-forming quasars, the host galaxy is solely responsible for obscuring the quasar.
The results provide new knowledge about the relationship between the growth of galaxies and the activity of black holes.
Obscured quasars may represent an early evolutionary stage, in which young galaxies are rich in cold gas and dust, which fuels high rates of star formation and black hole growth.
According to Professor David Alexander, from Durham University and co-author of the study, “this is a turbulent and disorderly phase of evolution, in which gas and stars collide and clump together in the center of the galaxy. The fight for cosmic food envelops the ‘baby’ quasar in its cocoon of dust.”
Unveiling these buried quasars will help scientists understand the connection between galaxies and the supermassive black holes at their hearts, the researchers conclude.
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