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Quasars Found Hiding Inside Host Galaxies, New Research Shows

A groundbreaking study led by Durham University astronomers has turned the spotlight on the mysterious world of quasars, supermassive black holes at the centers of galaxies. The research, published in the journal Monthly Notices of the Royal Astronomical Society, reveals that quasars can sometimes be hidden from view, not by the expected donut-shaped dust rings, but by their host galaxies themselves.

Artistic illustration of the thick dust torus thought to surround supermassive black holes and their accretion disks. [ESA / V. Beckmann (NASA-GSFC)] Credit: Durham University
Artistic illustration of the thick dust torus thought to surround supermassive black holes and their accretion disks. [ESA / V. Beckmann (NASA-GSFC)] Credit: Durham University

Quasars are celestial objects of intense fascination among astronomers. These brilliant sources of light are powered by supermassive black holes voraciously consuming the matter around them. However, their radiance can be obscured when thick clouds of gas and dust intervene, blocking the view of these enigmatic entities.


Traditionally, it was believed that this obscuring material existed primarily in the form of a "dusty torus," a ring-shaped structure of dust and gas surrounding the quasar's central black hole. However, this new research challenges that notion, suggesting that in some cases, the entire host galaxy is responsible for concealing the quasar.


To reach this groundbreaking conclusion, the team employed the Atacama Large Millimeter Array (ALMA) in Chile to observe a sample of quasars known for their intense rates of star formation. What they found was nothing short of revolutionary. Many of these quasars resided in extremely compact galaxies, often referred to as "starburst galaxies," measuring no more than 3000 light-years across.

Starburst galaxies are cosmic factories for stars, generating over 1000 sun-like stars each year. The formation of such a vast number of stars requires a significant amount of gas and dust, which serve as the fundamental building blocks for these celestial bodies. In these high-energy environments, clouds of gas and dust stirred up by rapid star formation can accumulate and entirely obscure the quasar.


Lead author of the study, Carolina Andonie, a Ph.D. student in the Center for Extragalactic Astronomy at Durham University, explained, "It's like the quasar is buried in its host galaxy. In some cases, the surrounding galaxy is so stuffed with gas and dust, not even X-rays can escape. We always thought the dusty donut around the black hole was the only thing hiding the quasar from view. Now we realize the entire galaxy can join in. This phenomenon only seems to happen when the quasar is undergoing an intense growth spurt."


The research suggests that in approximately 10-30% of rapidly star-forming quasars, the host galaxy is solely responsible for obscuring the quasar. This discovery has profound implications for our understanding of the relationship between galaxy growth and the activity of supermassive black holes.


Study co-author Professor David Alexander of Durham University explained, "It's a turbulent, messy phase of evolution, when gas and stars collide and cluster in the galaxy's center. The cosmic food fight cloaks the baby quasar in its natal cocoon of dust."


Revealing these buried quasars will enable scientists to gain a deeper insight into the intricate connection between galaxies and the supermassive black holes residing at their cores. This breakthrough discovery challenges established theories and offers a new perspective on the cosmic drama unfolding in the universe's most enigmatic corners.

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