Presskit: A star with an Extreme Orbit
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The image shows all known stars in the Galactic Center orbiting the central massive black hole Sgr A*. The central region is dominated by young, hot stars (blue), and a couple of cooler stars (orange/red). One of the cooler stars, S301, is approaching Sgr A* very closely, about the distance Sun to planet Saturn. Sgr A* itself is surrounded by hot plasma, the light of which is warped due to the black hole’s strong gravity.
© MPE
Image of the Galactic Center in July 2025. The highly eccentric, tight orbit of S301 around Sgr A* (colored in white), and the orbits of five other stars in the Galactic Center are shown.
This image shows the path of the S301 star around Sagittarius A*, the supermassive black hole at the centre of our galaxy. The diamonds show measurements performed with the GRAVITY instrument at ESO’s Very Large Telescope Interferometer (VLTI). The size of Neptune’s orbit is shown as a reference.
S301 orbits Sagittarius A* every 8 years. As it does so, its orbit rotates forming a rosette. This effect, known as Schwarzschild precession, had already been measured around Sagittarius A*, and it happens regardless of whether the black hole rotates or not.
However, if the black hole rotates there’s a different effect at play. As the black hole spins it drags and twists space-time around it, a phenomenon known as Lense-Thirring effect.
The S301 star ventures so close to the black hole that it could be affected by this phenomenon. The twisted space-time around the black hole would slightly change the orbit of S301 at each close passage. After several years, the difference between the predicted orbits for a non-rotating black hole and a rotating one would be small, about the size of Earth’s orbit around the Sun, but large enough that it could be measured with the VLTI and ESO’s Extremely Large Telescope (ELT), currently under construction.
S301 orbits Sagittarius A* every 8 years. As it does so, its orbit rotates forming a rosette. This effect, known as Schwarzschild precession, had already been measured around Sagittarius A*, and it happens regardless of whether the black hole rotates or not.
However, if the black hole rotates there’s a different effect at play. As the black hole spins it drags and twists space-time around it, a phenomenon known as Lense-Thirring effect.
The S301 star ventures so close to the black hole that it could be affected by this phenomenon. The twisted space-time around the black hole would slightly change the orbit of S301 at each close passage. After several years, the difference between the predicted orbits for a non-rotating black hole and a rotating one would be small, about the size of Earth’s orbit around the Sun, but large enough that it could be measured with the VLTI and ESO’s Extremely Large Telescope (ELT), currently under construction.
© ESO/GRAVITY collaboration/L. Calçada
ESO’s Very Large Telescope in front of the Galactic Center in the Milky Way. Four powerful lasers are shot into the night sky to remove disturbances of the atmosphere. These lasers are the Laser Guide Star (LGS) system as part of the GRAVITY+ project, the upgrade of GRAVITY.
© A. Berdeu/ESO
Laser-Show at Paranal
Credits: A. Berdeu/ESO
