Galaxy survives black hole party – for now

Black holes are thought to engulf so much surrounding material that they end the life of their host galaxy. During this process, they create a highly energetic object called a quasar, which was previously believed to stop star birth. Today, researchers have discovered a galaxy that survives the voracious forces of a quasar by continuing to spawn new stars – about 100 Sun-sized stars per year.

The discovery made by the Stratospheric Observatory for Infrared Astronomy (SOFIA) may explain how massive galaxies have emerged even though the Universe is dominated by galaxies that no longer form stars. The results are published in the Astrophysics Journal.

“This shows us that the growth of active black holes does not stop star birth instantly, which flies in the face of all current scientific predictions,” said Allison Kirkpatrick, assistant professor at the University of Kansas at Lawrence Kansas and study co-author. . “This leads us to rethink our theories on the evolution of galaxies.”

SOFIA, a joint project of NASA and the German Aerospace Center, DLR, studied an extremely distant galaxy, located more than 5.25 billion light years away, called CQ4479. At its base is a special type of quasar which was recently discovered by Kirkpatrick called a “cold quasar”. In this kind of quasar, the active black hole still feasts on material from its host galaxy, but the intense energy of the quasar has not ravaged all of the cold gas, so stars can continue to form and the galaxy is alive. This is the first time that researchers have examined a cold quasar in detail, directly measuring the growth of the black hole, the birth rate of stars and the amount of cold gas remaining to fuel the galaxy.

“We were surprised to see another strange galaxy that defies current theories,” said Kevin Cooke, postdoctoral researcher at the University of Kansas in Lawrence, Kansas, and lead author of this study. “If this tandem growth continues, the black hole and the stars surrounding it will triple in size before the galaxy reaches the end of its life.”

As one of the brightest and most distant objects in the universe, quasars, or “quasi-stellar radio sources,” are notoriously difficult to observe, as they often outshine everything around them. They form when a particularly active black hole consumes huge amounts of matter from its surrounding galaxy, creating strong gravitational forces. As more and more material spins faster and faster toward the center of the black hole, the material heats up and glows intensely. A quasar produces so much energy that it often outshines everything around it, blinding attempts to observe its host galaxy. Current theories predict that this energy heats up or expels the cold gas needed to create stars, stopping the birth of stars and dealing a fatal blow to the growth of a galaxy. But SOFIA reveals that there is a relatively short period during which the birth of the stars in the galaxy can continue while the black hole party continues to fuel the powerful forces of the quasar.

Rather than directly observing newborn stars, SOFIA used its 9-foot telescope to detect infrared light radiating from dust heated by the star-forming process. Using data collected by SOFIA’s High-resolution Airborne Wideband Camera-Plus or HAWC + instrument, scientists were able to estimate the amount of star formation over the past 100 million years.

“SOFIA allows us to see in that brief window of time where the two processes can coexist,” Cooke said. “It is the only telescope capable of studying the birth of stars in this galaxy without being overwhelmed by the intensely luminous quasar.”

The short window of joint growth of the black hole and the stars represents an early phase in the death of a galaxy, in which the galaxy has not yet succumbed to the devastating effects of the quasar. Ongoing research with SOFIA is needed to find out if many other galaxies go through a similar stage with a conjoined black hole and star growth before finally reaching the end of their lives. Future observations with the James Webb Space Telescope, scheduled to launch in 2021, would uncover how quasars affect the general shape of their host galaxies.

Provided by the Space Research Association of Universities