Astronomers have identified the fastest-known star in the Milky Way, a stellar object currently traveling at approximately 25,000 kilometers per second—or about 15,534 miles per second. Named S301, the star is orbiting the supermassive black hole at the center of the galaxy, known as Sagittarius A*, at speeds reaching roughly 8% of the speed of light.
Discovery of the Milky Way’s Fastest Star
The findings, published in the journal AP News, were uncovered using data collected by the European Southern Observatory’s Very Large Telescope Interferometer (VLTI) located at the Paranal Observatory in Chile’s Atacama Desert. According to researchers, S301 is approximately 50% more massive and five times brighter than the sun.
An Unprecedented Orbital Path
S301 is not only the fastest star discovered in the galaxy, but it also holds the record for the closest approach to Sagittarius A*. The star follows a highly eccentric, or lopsided, orbit that takes 8.7 years to complete. At its closest point to the black hole, S301 approaches within a distance roughly 11.5 to 12 times that of the Earth’s distance from the sun.
This proximity is significant, as it places the star in a region where it is sensitive to the extreme gravitational influence of the black hole. While black holes are often characterized as cosmic vacuum cleaners, Felix Mang, a PhD student at the Max Planck Institute for Extraterrestrial Physics (MPE), noted that S301 is not expected to cross the event horizon. Instead, it remains in a stable, albeit intense, orbital path.
Testing Einstein’s Theory of Relativity
The discovery of S301 provides a unique opportunity to test fundamental physics. According to Albert Einstein’s general theory of relativity, a spinning black hole drags spacetime along with it, a phenomenon that warps the orbits of nearby stars. This effect is only meaningful for objects at close range, making S301 an ideal candidate for study.
Dr. Stefan Gillessen, a senior scientist at MPE and co-author of the study, stated that the star’s tight, eccentric orbit could allow researchers to measure the spin of Sagittarius A* directly for the first time. Previously, scientists assumed that estimating the spin of the black hole would require tracking multiple stars over several decades. By tracing S301’s orbit back to 2017 and monitoring its next closest passage in 2031, researchers hope to secure the necessary data within the next decade.
Expanding the Search for Galactic Speedsters
Scientists have mapped the orbits of roughly 50 stars near the galaxy’s center out of several hundred that are sensitive to the black hole’s gravity. S301 is noted to be 10 times closer to Sagittarius A* than the previous record-holding star.
Experts suggest that the current findings represent only the beginning of such discoveries. Tuan Do, an astronomer at the University of California, Los Angeles, noted that as telescope technology improves, researchers will be able to pinpoint fainter stars that have previously eluded detection. Dr. Ziri Younsi, an astrophysicist at University College London, described the discovery as a gamechanger for understanding the evolution of the Milky Way, as measuring the black hole’s spin will offer new insights into the mysterious properties of the supermassive objects lurking at the center of large galaxies.
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