For the first time, astronomers have observed a blazar in action, substantiating a prevailing theory about how these luminous and energetic galactic cores work. A paper on the observations is published in the April 24 issue of Nature. Two University of Michigan astronomers contributed to the research, which was led by Alan Marscher of the Institute for Astrophysical Research at Boston University.

Blazars, among the most energetic objects in the universe, are fueled by supermassive black holes at the core of certain giant elliptical galaxies. Periodically, they emit jets of high-energy plasma at almost the speed of light. Competing theoretical models sought to explain how this phenomenon occurs.

One model predicted that the jets were propelled by magnetic fields that were twisted by the gravity of the black hole and the materials falling into it. This is the behavior the astronomers detected.

"What we've observed is the mechanism by which the acceleration of relativistic particles in the emanating jets occurs. Knowing that mechanism enhances our understand of the physics that goes into the acceleration process," said Hugh Aller, a professor in the U-M Department of Astronomy.

Relativistic particles are particles traveling close to the speed of light.

"Often, we'd observe blazars, but they didn't do anything. It's been difficult to catch these outbursts when they occur," he added.

Scientists from across the globe aimed a variety of telescopes at the blazar BL Lacertae, about 950 million light-years away from Earth. Optical, X-ray and radio telescopes monitored the galaxy at different electromagnetic wavelengths periodically for several years. U-M recorded radio light curves at the Radio Astronomy Observatory at Peach Mountain in Dexter.

"This is the first observational evidence that really fits with the picture that the theoreticians have had," said Margo Aller, a research scientist and lecturer in the U-M Department of Astronomy. "The reason we have this evidence is a very fine sampling of a large number of instruments, including the Michigan radio telescopes."

Scientists hope to get a closer look at blazar jets when NASA launches its Gamma-ray Large Area Space Telescope (GLAST) satellite observatory in May.