Researchers using ESO’s GRAVITY instrument on the VLT have tracked a star named S301 in a tight orbit around the Milky Way’s central black hole, Sgr A*, making it the closest and fastest known star in that region.

If confirmed, S301’s orbit could yield the first direct measurement of Sgr A*’s spin within about a decade, enabling a new, precise test of relativistic physics in extreme spacetime.

Future observations aim to capture at least two full orbits by around 2031 to map S301’s path and directly infer the black hole’s rotation, testing Einstein’s General Theory of Relativity.

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The findings were published in Nature on August 19.

The discovery was made with data from the ESO’s Very Large Telescope Interferometer (VLTI) in Chile and analyzed by researchers led by Stefan Gillessen at the Max Planck Institute for Extraterrestrial Physics, with Nature as the publication.

Observations were conducted with the VLTI at Paranal, combining four 8-meter telescopes to achieve high-resolution measurements.

The Nature article notes collaboration with the Max Planck Institute and ESO VLTI/GRAVITY+ observations supporting the discovery.

GRAVITY+ collaboration began detecting S301 in 2023, requiring about two years of data to confirm its unusual nature amid weak signals.

Spring 2023 marked the discovery using the GRAVITY instrument on the VLTI, which links four telescopes into a high-resolution virtual telescope.

The VLTI/GRAVITY+ technique enables precise tracking of S301 over several years, forming the basis for potential spin measurements.

Reinhard Genzel emphasizes that S301 opens a new window into spacetime near Sgr A* and demonstrates the growing precision of orbital measurements around the Galactic center.