Fastest known Milky Way star offers new test of supermassive black hole's spin

Astronomers have discovered the fastest known star in the Milky Way, S301, orbiting the supermassive black hole at the center of our galaxy. The star reaches speeds of 25,000 km/s (15,500 miles per second) as it travels around the black hole. It comes closer to the black hole than any other star observed before, approaching it at a distance similar to Saturn's distance from the Sun. This discovery offers a rare chance to test the spin of Sagittarius A* using a star that orbits so closely. The study was conducted using the European Southern Observatory's Very Large Telescope Interferometer (ESO's VLTI), and the star was tracked using the GRAVITY instrument. The discovery is significant as it allows for a direct measurement of the black hole's rotation, which is a key test of Einstein's general theory of relativity.

• S301 orbits Sagittarius A* every 8.7 years.
• It approaches the black hole at a distance similar to Saturn's distance from the Sun.
• The star moves at more than 8% the speed of light at its closest approach.
• The VLTI's GRAVITY instrument was used to track S301 and measure its orbit.
• The study was conducted by a collaboration including the Max Planck Institute for Extraterrestrial Physics (MPE) and other observatories.

The discovery highlights the importance of observing stars in close proximity to supermassive black holes to test fundamental physics. The star's orbit and its extreme proximity to the black hole provide a unique opportunity to measure the black hole's spin directly. The study's findings could lead to new insights into the nature of black holes and the behavior of spacetime around them. The research was published in Nature, and the team plans to continue observing S301 in the coming years to refine their measurements.

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