Astronomers have identified a star that sets new records for both speed and proximity in orbit around Sagittarius A*, the supermassive black hole at the center of the Milky Way. The star, designated S301, is the closest and fastest ever seen circling the black hole, according to reports published in the journal Nature on August 19.
S301 completes a full orbit every 8.7 years, whisking past the black hole at a velocity of about 55 million miles (90 million kilometers) per hour, a speed equivalent to roughly 8% the speed of light. Its orbit is so tightly bound that, within about a decade, researchers anticipate they will be able to measure the star's rotation rate.
The discovery was described by Live Science, which highlighted the star's remarkable speed and closeness to Sagittarius A*, the 4.3 million-solar-mass black hole at the heart of our galaxy. A detailed account of the research was also provided by CNET, reporting that the star was detected by researchers at the Max Planck Institute for Extraterrestrial Physics in Germany.
As reported by CNET, S301's peak velocity is estimated at about 15,500 miles per second, or around 55.8 million miles per hour. The star reaches these extraordinary speeds as it approaches Sagittarius A*, accelerating due to the black hole's gravitational pull before executing a sharp turn to complete its orbit. It then slows down as it takes a wider loop, continuing its long journey.
The discovery and its significance
S301's orbit brings it about 10 times closer to the black hole than the previous record-holder, a star called S2, according to the CNET report. This unusual proximity places the star in a region of space where the gravitational effects are extreme, offering a unique testbed for theories of strong gravity.
The star appears as a faint object, approximately two billion times dimmer than Betelgeuse, yet it stands out not for its brightness but for its speed and orbital dynamics.
The detection of the star was made using the Gravity instrument on the Very Large Telescope and the Micado instrument on the Extremely Large Telescope, both located in Chile as part of the European Southern Observatory, as reported by CNET.
The path to measuring the spinning black hole
The new finding points toward a future ability to probe one of the most intriguing predictions of general relativity: the Lense-Thirring effect, which shapes the fabric of spacetime around a rotating massive body.
Felix Mang, a PhD student and corresponding author of the study, emphasized the star's unique position in an area where frame-dragging is particularly intense. He was quoted by CNET as saying, "S301 is the first star to orbit directly in the region around Sagittarius A* where the frame-dragging effect is extreme. We're not just measuring spacetime curvature; we are measuring how it gets distorted by the rotation of the black hole itself. That is unique."
According to CNET's report, researchers have already measured the Lense-Thirring effect on S301, marking a first for any star in this extreme environment. This effect, a consequence of general relativity, describes how a rotating black hole drags spacetime along with it as it spins.
However, the study also suggests that the star's exceptionally close orbit could allow astronomers to measure the star's spin rate within about a decade, offering additional insight into the black hole's own rotation and its influence on surrounding matter.
The star's speed in cosmic context
The speed of S301 is a glimpse of how fast objects can travel when subject to extreme gravitational force. To put this in context, the previous record for the fastest-moving celestial object was held by a low-mass star accompanied by a super Neptune planet, moving at roughly 1.2 million miles per hour (about 333 miles per second), as reported by CNET.
The solar system travels through space at approximately 500,000 miles per hour (140 miles per second), CNET described, while the fastest human-made object, the Parker Solar Probe, achieves a speed of 430,000 miles per hour—all amounts as less than S301's speed.
Those numbers frame S301's extreme nature, but the star's significance goes beyond velocity. Its orbit, so close to the heart of the Milky Way's central black hole, offers a information-rich environment for testing the laws of physics under conditions that can exist nowhere else in our galaxy.
As the research team continues to observe S301, its future measurements could confirm the likely spin of Sagittarius A* and perhaps other properties that remain hidden. The star's existence itself is a testament to the extremes of the universe, but they happen right in our own galactic backyard.