Updated

Updated · CNET · Aug 22

S301 Becomes Fastest Known Star at 15,500 Miles a Second, Skimming 10 Times Closer to Sagittarius A*

Updated

Updated · CNET · Aug 22

S301 Becomes Fastest Known Star at 15,500 Miles a Second, Skimming 10 Times Closer to Sagittarius A*

Q: What happened to the mysterious companion star violently ejected when S301 was captured by the black hole?

No one knows for sure yet. The leading explanation is that when the binary system was torn apart by Sagittarius A* through the Hills mechanism, S301 was captured into its tight orbit and the other star was flung away as a hypervelocity star, likely fast enough to escape the Milky Way. There is no confirmed detection of that companion in the new discovery paper. Researchers infer its existence from S301’s highly eccentric orbit, which is the kind of orbit expected after a binary disruption near a supermassive black hole. In that scenario, the companion would now be far from the Galactic Center and difficult to identify with certainty. There is, however, an intriguing candidate. A 2026 arXiv study argues that S301 could be the bound companion of the known hypervelocity star S5-HVS1, one of the few stars whose trajectory points clearly back to the Galactic Center. The authors say S301’s orbit and estimated mass are consistent with what would be expected if S5-HVS1 were the ejected partner. But they also stress that the evidence is not yet decisive. So the best current answer is that the companion was probably hurled outward as a hypervelocity star and may even have left the galaxy. It may possibly be S5-HVS1, but that link remains unconfirmed pending better mass measurements, chemical comparisons, and further orbital data.

3 articles · Updated · CNET · Aug 22

15,500 miles per second is S301’s peak speed near the Milky Way’s central black hole, making it the fastest star or planet ever observed.
10 times closer to Sagittarius A* than the previous record-holder S2, the dim star gives researchers an unusually direct probe of the black hole’s gravity and rotation.
Max Planck researchers said S301 is close enough to measure the Lense-Thirring frame-dragging effect, letting them test aspects of Einstein’s general relativity that other nearby objects could not.
Two billion times dimmer than Betelgeuse, S301 required instruments including ESO’s Gravity and Micado in Chile, and scientists hope a decade of follow-up will reveal more about how black holes distort spacetime.