UNIVERSITY PARK, Pa. — Some supermassive black holes launch powerful beams of material, or jets, away from them, while others do not. Astronomers may now have identified why.
Using data from NASA’s Chandra X-ray Observatory, ESA’s XMM-Newton, Germany’s ROentgen SATellite (ROSAT), the NSF's Karl G. Jansky Very Large Array, the Sloan Digital Sky Survey, and other telescopes, researchers have studied more than 700 quasars — rapidly growing supermassive black holes — to isolate the factors that determine why these black holes launch jets.
Jets from supermassive black holes can inject huge amounts of energy into their surroundings and strongly influence the evolution of their environments. Previously, scientists realized that a supermassive black hole needs to be spinning rapidly to drive strong jets — but not all rapidly spinning black holes have jets.
“We found there’s another determining factor of whether a supermassive black hole has jets, something called a black hole corona threaded by magnetic fields,” said Shifu Zhu, a graduate student at Penn State and the leader of the study. “If you don’t have a black hole corona that’s bright in X-rays, it seems like you don’t have powerful black hole jets.”
In astronomy, the term “corona” is commonly associated with the outer atmosphere of the Sun. Black hole coronas, on the other hand, are regions of diffuse hot gas that lie above and below a much denser disk of material swirling around the gravitational sinkhole. Like the corona around the Sun, black hole coronas are threaded with strong magnetic fields.
“It’s like baking bread where you need a few ingredients to successfully follow the recipe for a loaf,” said co-author Niel Brandt, Verne M. Willaman Professor of Astronomy and Astrophysics and professor of physics at Penn State. “Our results show that one ingredient you can’t do without when ‘making’ powerful quasar jets is a bright corona.”
The team obtained their results by gaining a better understanding of X-ray emission from quasars. Previous studies had shown that quasars without jets show a characteristic link between the strength of their X-ray and ultraviolet emission. This correlation is explained by ultraviolet light from the disk of the black hole striking particles in the corona. The resulting energy boost converts the ultraviolet light to X-rays.
In the new study the team chose to investigate the behavior of quasars that do have jets. They found a correlation between how bright the different quasars are in X-rays and ultraviolet light that is remarkably similar to that found for quasars without jets. They concluded that the X-ray emission in the jet-powering quasars is also produced by a black hole corona.