Mapping the magnetic field of our galaxy’s supermassive black hole

Artist's impression of a pulsar (the smaller object at the right) orbiting the central black hole of the Milky Way. The beams of light represent the pulses, which are affected by the magnetic field surrounding the black hole.

Bill Saxton, NRAO/AUI/NSF

The black hole at the center of the Milky Way is a bright source of radio and X-ray light. According to theory, this light is emitted due to hot gas orbiting and falling into the black hole. However, the shape of the gas flow is dictated by the magnetic fields at the galactic center, which are difficult to measure.

Astronomers hoped fondly for the discovery of a pulsar, a rapidly rotating remnant of a dead star, which generates powerful jets of radio photons. Any magnetic field near the pulsar would affect the radio emissions, allowing researchers to map the environment near the black hole.

The wish was granted earlier this year when an X-ray flare revealed the presence of a pulsar within one light-year of the Milky Way's black hole. R.P. Eatough and colleagues measured the light from the pulsar and found it was strongly rotated, a sure sign of a magnetic field. The magnetic field they detected—if it extends to the surface of the black hole—would be sufficient to explain the entire spectrum of emissions from the Milky Way's center.