“We always thought the dusty donut around the black hole was the only thing hiding the quasar [supermassive black holes at the centres of galaxies] from view. Now we realize the entire galaxy can join in.”

New Study Says Supermassive Black Holes Can Be Found Buried In Their Host Galaxies

A recent investigation reveals that within the hearts of galaxies, supermassive black holes, also known as quasars, can occasionally be concealed by dense gas and dust clouds.

This discovery challenges the conventional belief that quasars are exclusively obscured by donut-shaped rings of dust in their immediate vicinity.

Quasars are luminous celestial objects fueled by voracious black holes that feed on the matter surrounding them. Their intense radiation can be obstructed when dense clouds intervene between us and the quasar.

Until now, it was widely assumed that this obscuring material resided solely in the immediate surroundings of the quasar, forming a dusty torus encircling it.

However, a group of scientists, led by Durham University, has gathered evidence suggesting that in certain quasars, the obscuration arises primarily from the host galaxy itself, in which the quasar is situated.

Using the Atacama Large Millimeter Array (ALMA) in Chile, they observed a collection of heavily dust-shrouded quasars that displayed exceptionally high rates of star formation.

Their observations unveiled that many of these quasars inhabit remarkably compact galaxies, often referred to as “starburst galaxies,” measuring no more than 3,000 light-years across.

In these starburst galaxies, the conditions are ideal for the formation of over a thousand stars, similar to our Sun, each year. To facilitate the birth of such a large number of stars, a substantial amount of gas and dust, which serves as the essential building material for stars, is required.

In these galaxies, the clouds of gas and dust, agitated by the rapid star formation, can accumulate to a point where they entirely conceal the quasar. The comprehensive study detailing these findings has been published in the journal MNRAS.

Carolina Andonie, the lead author of the study and a PhD student at Durham University’s Centre for Extragalactic Astronomy, described the situation as akin to the quasar being buried within its host galaxy.

She stated, “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. This phenomenon only seems to happen when the quasar is undergoing an intense growth spurt.”

The research team approximates that the host galaxy alone plays a role in obscuring the quasar in roughly 10-30% of vigorously star-forming quasars.

These findings offer new perspectives on the interplay between the expansion of galaxies and the activity of black holes.

Obscured quasars may signify an early stage of development, during which young galaxies are rich in cold gas and dust, providing the fuel for both high rates of star formation and black hole growth.

Professor David Alexander, a co-author of the study from Durham University, described this phase as “a turbulent, messy phase of evolution,” marked by the interaction and clustering of gas and stars at the center of the galaxy.

He stated, “The cosmic food fight cloaks the baby quasar in its natal cocoon of dust.”

Uncovering these concealed quasars is expected to offer a deeper understanding of the relationship between galaxies and the supermassive black holes that inhabit their cores.

Image Credit: DURHAM UNIVERSITY