Pinball on a Galactic Scale

Reporting in this week's issue of Astrophysical Journal Letters, a team led by David Ballantyne of the University of Arizona in Tucson concludes that the Milky Way's central black hole is strong enough to generate a powerful but chaotic magnetic field that extends out a distance of about 10 light-years. To reach their conclusions, the researchers used computer programs to calculate the hypothetical trajectories of some 220,000 protons, which are ejected from the Milky Way's black hole and get bounced around by its magnetic field like in a galactic-sized version of a pinball machine. They then compared those paths with recent observations by ground-based instruments of the location of the gamma-rays and found that 69% of the computer-generated trajectories matched what the observed data were showing. The protons were slamming into hydrogen atoms within huge clouds of gas that slowly orbit the black hole about 10 light-years out. These collisions produce the gamma radiation astronomers have observed at the center of the Milky Way.