Supermassive black holes, known as quasars, found at the centers of galaxies can sometimes be hidden by dense clouds of gas and dust in their host galaxies, according to a new study. This challenges the widely held belief that quasars are obscured only by donut-shaped rings of dust in the immediate vicinity of the black hole.

Quasars are extremely bright objects powered by black holes that absorb matter around them. If thick clouds come between us and the quasar, their strong radiation can be blocked. Astronomers have long believed that this dark matter exists only in the immediate vicinity of the quasar, in the “dust torus” (or donut) surrounding it.

Now a team of scientists led by Durham University has found evidence that the dimming in some quasars is caused entirely by the host galaxy in which the quasar is located. Using the Atacama Large Millimeter Array (ALMA) in Chile, they observed a sample of very dusty quasars with intense star formation rates. They found that most of these quasars are located in very compact galaxies no more than 3000 light-years in diameter, known as “starburst galaxies.” These starburst galaxies can produce more than 1,000 Sun-like stars per year.

In order for a galaxy to form so many stars, it needs large amounts of gas and dust, the building blocks of stars. In such galaxies, clouds of gas and dust caused by rapid star formation can accumulate and completely obscure the quasar.

The full text of the research was published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS). The study’s lead author is Carolina Andoni, Ph.D. student at Durham University’s Center for Extragalactic Astronomy, said: “It’s as if a quasar had become embedded in its host galaxy. In some cases, the surrounding galaxy is so saturated with gas and dust that not even X-rays can escape. We always thought that the dusty donuts around the black hole were the only thing hiding the quasar from view. We now understand that the entire galaxy can participate. “This phenomenon appears to occur only when the quasar undergoes an intense growth spurt.”

The team estimates that in about 10-30% of very fast star-forming quasars, the host galaxy is solely responsible for dimming the quasar. The data obtained allows a new understanding of the connection between the growth of galaxies and the activity of black holes. Nebular quasars may represent an early stage of evolution when young galaxies are rich in cold gas and dust, allowing high rates of star formation and black hole growth.

Study co-author Professor David Alexander of Durham University said: “This is a turbulent, chaotic phase of evolution in which gas and stars collide and gather together at the center of the galaxy. A cosmic scramble for food allows a baby quasar to hide inside its ancestral dust cocoon.” .”

The discovery of these hidden quasars will help scientists understand the connection between galaxies and the supermassive black holes at their hearts. Source