The jets produced by supermassive black holes deep in the nucleus of distant active galaxies are the most violent and energetic objects known. Although supermassive black holes are billions of times more massive than our Sun, they occupy a space no larger than our solar system. These rapidly rotating black holes attract stars, gas, and dust, creating huge magnetic fields. Magnetic forces can trap some of the infalling gas and focus it into narrow radio-emitting jets that flow away from the core of the galaxy at velocities approaching the speed of light. For decades, astronomers have wondered about the nature of these jets and if they also emit radiation in other parts of the electromagnetic spectrum.
Prof. Matthew Lister is part of an international team of astronomers that have made new observations to reveal further details about these jets and their function. The team has used a combination of data from NASA's orbiting Fermi Gamma-ray Space Telescope and the ground-based Very Long Baseline Array (VLBA) radio telescope to investigate the production of gamma rays by supermassive black holes. In findings reported in the 1 May 2009 issue of Astrophysical Journal Letters, the team observed material expelled at enormous speeds away from black holes in the heart of very remote galaxies. These ejections assume the form of narrow jets in VLBA images and appear to produce gamma-rays detected by Fermi.
The active galaxies detected by Fermi generally possess faster and more compact radio jets. In addition, the radio jets tend to be brighter in the months following gamma-ray flares. This information is being used to understand exactly how and where some of the highest energy photons in our universe are created. "For more than a decade, we have collected images of the brightest galaxies in the radio sky to study the changing structure of their jets," said Lister, who lead the MOJAVE program at the VLBA and is also a guest investigator on Fermi. "We've waited a long-time to compare our measurements with the findings in the gamma-ray sky – and now, thanks to this state-of-the-art space observatory, we finally can."