German astronomers track star racing near Milky Way's central black hole

Scientists from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, have monitored the star known as S301 as it approached Sagittarius A, the supermassive black hole at the center of the Milky Way. Using the European Southern Observatory’s Very Large Telescope Interferometer, they measured the star accelerating to more than 15,500 miles per second—roughly 8 % of the speed of light—making it the fastest macroscopic object recorded in the galaxy.

Because S301 follows an 8.7-year orbit, its behavior provides a unique test of the black hole’s gravitational influence and may expose the elusive spin of Sagittarius A. While theory predicts black holes should rotate, direct evidence has been lacking; the star’s dynamics could fill that gap and shed light on how the black hole acquired its mass and why it is currently dormant. Senior staff scientist Stefan Gillessen noted that understanding the spin will also illuminate the co-evolution of black holes and their host galaxies. The study appears in the journal Nature and points to future efforts to measure the spin more precisely.