Full Breakdown
Record-Breaking Star S301 Discovered
8/22/2026, 12:36:10 AM
Discovery and Orbital Characteristics
Astronomers identified a faint star S301 orbiting the Milky Way’s central black hole, Sagittarius A\*. It reaches ? 25,000 km s?¹ (? 8 % c) at pericenter and completes an orbit in 8.7 years. Its highly elongated trajectory brings it to within ? 12 AU of the black hole—the closest known stellar probe of its gravity. S301 was first spotted in 2023 with the VLT Interferometer (GRAVITY+) and its path was reconstructed from detections dating back to 2017. The black hole’s mass is ? 4.3 million M? at a distance of ? 26,000 ly from Earth.
Background & Context
“S-stars” near Sagittarius A\* have been used to test general relativity. The best-studied, S2, has a 12-year orbit and confirmed Schwarzschild precession. Relativistic frame-dragging (Lense-Thirring) declines sharply with distance, making it hard to detect with more distant stars. S301’s proximity makes it roughly 100 times more sensitive to the black hole’s spacetime curvature, offering a practical route to measuring the spin.
Data & Statistics
- Maximum speed: 25,000 km s?¹ (? 8 % c)
- Orbital period: 8.7 years
- Pericenter distance: ? 12 AU (? 136–142 Schwarzschild radii)
- Predicted Schwarzschild precession: ? 2° per orbit
- Maximum Lense-Thirring shift (maximal spin): ? 0.11° per orbit
- Projected spin-parameter uncertainty: < 0.2, orientation ? ±30° by ~2035
- Next close approach: 2031
Why It Matters / Impact
Tracking S301 precisely could yield the first **direct stellar-dynamics measurement of Sagittarius A\*’s spin, testing the no-hair theorem** and informing models of black-hole growth and jet formation. The star also serves as a laboratory for studying how extreme gravity influences stellar motion and may reveal any extended mass distribution near the galactic centre.
Official Statements & Responses
- Reinhard Genzel, Nobel-winning director of MPE, called the discovery a “breakthrough” for testing Einstein’s theory around a rotating supermassive black hole.
- Juan Osorno, astronomer at LIRA Observatoire de Paris, noted that without S301, decades of monitoring multiple stars would be required to approach a spin measurement.
Verbatim Quotes
- “What is special about this star is that it’s orbiting Sagittarius A* on a very tight orbit, taking just 8.7 years to complete it,” — Felix Mang, study author
- “For the first time, we would actually be able to measure very directly the spin of a massive black hole, which would be a key test of Einstein’s theory,” — Dr Stefan Gillessen, MPE researcher
What’s Next
The 2031 pericenter will provide the strongest relativistic signal. Upgraded GRAVITY+ capabilities, combined with high-resolution spectroscopy from the forthcoming Extremely Large Telescope (ELT) and its MICADO instrument, are expected to deliver astrometry precise enough to isolate the tiny frame-dragging shift. Continued monitoring over two full orbits should constrain the spin parameter to the projected uncertainty within the next decade.
