How tracking 30 stars proved a supermassive black hole exists
For sixteen years, astronomers have watched stars dance around the Milky Way's center. By mapping these orbits with unprecedented precision, researchers have finally unraveled the secrets of the monster lurking at our galaxy's heart, providing some of the strongest evidence yet for the existence of a supermassive black hole.
At the center of our galaxy lies Sagittarius A*, a supermassive black hole that remains one of the most enigmatic objects in the universe. To study it, a team of German astronomers, led by Reinhard Genzel of the Max Planck Institute for Extramundane Physics, embarked on a massive longitudinal study. By tracking the motions of nearly 30 stars—a five-fold increase compared to previous research—the team used these stars as 'test particles' to map the gravitational forces at play (S2:p2, S2:p4).
The challenge of observing this region is significant. Thick interstellar dust obscures the Galactic Centre in visible light, forcing astronomers to use infrared wavelengths to penetrate the haze (S2:p3). Using data gathered from 1992 onwards, including observations from the 3.5-metre New Technology Telescope and the 8.2-metre Very Large Telescope, the researchers were able to calculate precise orbits (S2:p6). This long-term effort allowed them to observe at least one star complete a full orbit around the central mass (S2:p2).
The findings are profound. The study reveals a central mass concentration of approximately four million solar masses (S2:p5). Crucially, the data shows that at least 95% of the mass sensed by these stars must reside within the black hole itself, leaving very little room for other dark matter (S2:p4). This level of detail also allowed the team to pinpoint our distance to the Galactic Centre at 27,000 light-years (S2:p5). Beyond proving the black hole's existence, the study provides a unique laboratory to study stellar dynamics and strong gravity (S2:p3).
Source: ESOcast 2: Unprecedented 16-year long study tracks stars orbiting Milky Way black hole
