Jets of particles streaming out of bright galaxies operate differently than previously thought. This revelation will help theorists craft better models of how the universe's biggest accelerators work.

Jets of particles streaming from black holes in far-away galaxies operate differently than previously thought, according to recent work led by scientists at the Kavli Institute for Particle Astrophysics and Cosmology, jointly located at SLAC and Stanford University. The study, which included data from more than 20 telescopes, reveals that most of the jet's light—gamma rays, the universe's most energetic form of light—is created much farther from the black hole than expected.

High above the flat Milky Way galaxy, bright galaxies called blazars dominate the gamma-ray sky, discrete spots on the dark backdrop of the universe. As nearby matter falls into the black hole at the center of a blazar, "feeding" the black hole, it sprays some of this energy back out into the universe as a jet of particles.

Researchers had previously theorized that such jets are held together by strong magnetic field tendrils, while the jet's light is created by particles revolving around these wisp-thin magnetic field "lines." Yet, until now, the details have been relatively poorly understood.

Over a full year of observations, the researchers focused on one particular blazar jet, located in the constellation Virgo, monitoring it in many different wavelengths of light: gamma-ray, X-ray, optical, infrared and radio. Midway through the year, researchers observed a spectacular change in the jet's optical and gamma-ray emission: a 20-day-long flare in gamma rays was accompanied by a dramatic change in the directionality of the jet's optical light.

This temporal connection between changes in the gamma-ray light and changes in the optical light suggests that both types of light are created in the same geographical region of the jet.

Researchers previously thought that the gamma rays must be released near the black hole, close to where the matter flowing into the black hole gives up its energy in the first place. Yet the new results suggest that, like optical light, the gamma rays are emitted relatively far from the black hole. This in turn suggests that the magnetic field lines must somehow help the energy travel far from the black hole before it is released in the form of gamma rays.

This work offers theorists the insight they need to craft better models of how the universe's biggest accelerators work.

Source: Stanford University