Combined X-ray studies and supercomputer simulations track 12 billion years of cosmic black hole growth

By combining X-ray observations with state-of-the-art supercomputer simulations of galaxy construction throughout cosmic history, researchers have produced the best modeling yet of the growth of the supermassive black holes at the centers of galaxies. Using this hybrid approach, a research team led by Penn State astronomers has created a complete picture of black hole growth over 12 billion years, from the universe’s infancy at about 1.8 billion years old to the present at 13.8 billion years old.

The research consists of two articles, one of which was published in The Astrophysical Journal, and one that has not yet been published and will be submitted to the same journal. The results will be presented at the 244th meeting of the American Astronomical Society, held June 9-13 at the Monona Terrace Convention Center in Madison, Wisconsin.

“Supermassive black holes at the centers of galaxies have millions to billions of times the mass of the Sun,” said Fan Zou, a graduate student at Penn State and first author of the papers. “How do they become such monsters? This is a question astronomers have been studying for decades, but it’s been difficult to track all the ways black holes can grow reliably.”

Supermassive black holes grow through a combination of two main channels. They consume cold gas from their host galaxy – a process called accretion – and can merge with other supermassive black holes when galaxies collide.

“During the process of consuming gas from their host galaxies, black holes emit strong of Astronomy and Astrophysics. physics at Penn State and leader of the research team. “We measured accretion-induced growth using sky X-ray survey data collected over more than two decades from three of the most powerful X-ray facilities ever launched into space.”

The research team used additional data from NASA’s Chandra In total, they measured accretion-induced growth in a sample of 1.3 million galaxies containing more than 8,000 fast-growing black holes.

“All galaxies and black holes in our sample are very well characterized at multiple wavelengths, with excellent measurements in the infrared, optical, ultraviolet and X-ray bands,” Zou said. ‘This allows for robust conclusions, and the data shows that more massive galaxies grew their black holes faster at all cosmic epochs. The quality of the data allowed us to quantify this important phenomenon much better than in previous studies. .”

The second way supermassive black holes grow is through mergers, where two supermassive black holes collide and merge to form a single, even more massive black hole. To track merger growth, the team used IllustrisTNG, a series of supercomputer simulations that model the formation, evolution and mergers of galaxies from shortly after the Big Bang to the present.

“In our hybrid approach, we combine the observed growth from accretion with the simulated growth from mergers to reproduce the growth history of supermassive black holes,” Brandt said. “With this new approach, we believe we have achieved the most realistic view of supermassive black hole growth to date.”

The researchers found that in most cases, accretion dominated black hole growth. Mergers have made notable secondary contributions, especially over the past 5 billion years of cosmic time for the most massive black holes. Overall, supermassive black holes of all masses grew much faster when the universe was younger. This almost stopped the total number of supermassive black holes by 7 billion years ago, while many new ones were still appearing in the universe earlier.

“Our approach allows us to track how central black holes in the local universe have most likely grown over cosmic time,” Zou said. ‘As an example, we looked at the growth of the supermassive black hole at the center of our Milky Way Galaxy, which has a mass of 4 million solar masses. Our results indicate that our galaxy’s black hole most likely grew relatively late in cosmic time. “

In addition to Zou and Brandt, the research team includes Zhibo Yu, a graduate student at Penn State; Hyungsuk Tak, assistant professor of statistics and astronomy and astrophysics at Penn State; Elena Gallo at the University of Michigan; Bin Luo at Nanjing University in China; Qingling Ni of the Max Planck Institute for Extraterrestrial Physics in Germany; Yongquan Xue at the University of Science and Technology of China; and Guang Yang at the University of Groningen in the Netherlands.