Astronomers studying the heart of the Milky Way galaxy have tracked high-speed stars whipping around Sagittarius A*, the supermassive black hole located approximately 26,000 light-years from Earth. Researchers using advanced European Southern Observatory’s Very Large Telescope facilities have mapped stellar orbits in this extreme environment, revealing objects moving at astonishing velocities under the influence of intense gravitational forces.
Tracing High-Speed Stars Near the Milky Way’s Central Black Hole
Among these galactic inhabitants is a star designated as S301, which researchers describe as the fastest star ever observed in the galaxy. According to findings published in the journal NPR by astronomer Stefan Gillessen and his colleagues at the Max Planck Institute for Extraterrestrial Physics, S301 reaches speeds exceeding 15,000 miles per second at its closest approach—representing just shy of 8 percent of the speed of light.
The Extreme Orbit of S301
The newly observed star traces an exceptionally elongated elliptical orbit lasting 8.7 years. Gillessen noted that the star approaches the black hole from one direction, accelerates rapidly, and executes a sharp turn around the central mass before flying back outward to decelerate at its furthest point.
Scientists note that this proximity allows researchers to use the star as a probe to visualize how gravity acts on space and time. Because the object orbits significantly closer to the black hole than previous record holders, it experiences heightened relativistic effects. The central supermassive object itself contains roughly four million times the mass of our Sun, creating a gravitational potential capable of accelerating passing bodies to extreme fractions of light speed.
A Cluster of Squeezars
S301 belongs to a population of stars clustered near the galactic center that follow eccentric, highly elongated paths around Sagittarius A*. First suggested by scientists Tal Alexander and Mark Morris in 2003, these objects have been dubbed “squeezars.” Over years of observation, researchers have identified multiple stars in this cluster, including S2 (also known as S0-2), S4711, S4713, S4714, S4715, and S4716.
While S2 reaches speeds of roughly 3 percent of the speed of light—about 16 million miles per hour—and completes an orbit in roughly 16 years, newer discoveries like S4716 orbit the black hole once every four years. Observing these compact orbits required specialized instrumentation, including combined telescope arrays on Mauna Kea in Hawai’i and in Chile.
Testing General Relativity
The presence of rapidly moving stars near Sagittarius A* provides a crucial laboratory for testing Albert Einstein’s theories of relativity. When stars such as S2 pass close to the event horizon—reaching distances roughly 120 times the separation between Earth and the Sun—their emitted light undergoes measurable gravitational redshifts.
University of California astronomers, including a team led by UCLA astronomer Andrea Ghez alongside UC Berkeley’s Jessica Lu, have analyzed these phenomena to confirm that observed stellar motions and light behaviors match the predictions of general relativity. However, researchers emphasize that studying these high-speed stellar probes may ultimately reveal where Einstein’s framework requires expansion to fully explain the nature of black holes.
