Astronomers have found what is currently the fastest known star in the Milky Way, a faint star racing through the extreme environment around Sagittarius A*, the supermassive black hole at the centre of our galaxy.
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what → find → galaxy
Called S301, the star reaches a staggering speed of about 15,500 miles per second, or 25,000 kilometres per second, which is more than 8% of the speed of light.
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which → call → light
It completes an unusually tight orbit around the black hole in just 8.7 years and comes closer to Sagittarius A* than any other known star.
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It → complete → star
The discovery could give scientists a rare opportunity to study the effects of a spinning black hole and potentially test one of the predictions of Albert Einstein's general theory of relativity.
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discovery → give → relativity
Scientists found a star travelling at 15,500 miles per second
S301 is a faint star orbiting Sagittarius A*, which has a mass roughly 4.3 million times that of the Sun.
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which → find → Sun
The star reaches its highest speed when it gets closest to the black hole, travelling at about 25,000 kilometres per second.
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it → reach → second
That works out to roughly 56 million miles per hour and more than 8% of the speed of light.
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That → work → light
The star's orbit is highly stretched rather than circular, meaning it spends much of its journey farther from the black hole before making a rapid close pass.
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it → mean → pass
At its closest approach, S301 comes to roughly 12 times the distance between Earth and the Sun, or about 1.8 billion kilometres.
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S301 → come → Earth
S301 takes only 8.7 years to complete one trip around Sagittarius A*.
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S301 → take → *
What makes its orbit particularly important is how close the star comes to the black hole.
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star → make → hole
Its closest approach is unprecedented among the known stars orbiting Sagittarius A*.
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approach → know → *
The enormous gravity of the 4.3-million-solar-mass black hole accelerates the star to its record speed as it approaches.
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it → accelerate → speed
Despite coming extremely close on astronomical scales, S301 does not simply fall into Sagittarius A*.
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S301 → come → *
Its speed carries it through the closest part of its orbit and back out again.
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speed → carry → orbit
Researchers believe the star's highly elongated path could also provide clues about its past and how it ended up so close to the centre of the Milky Way.
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it → believe → Way
Scientists used observations dating back to 2017
Researchers identified S301 using the GRAVITY instrument on the European Southern Observatory's Very Large Telescope Interferometer in Chile.
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Researchers → use → Chile
The team first spotted the star in observations from 2023 and then searched older observations, finding it in data from 2021 and 2017.
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team → spot → 2021
Combining these measurements allowed astronomers to work out the star's path around Sagittarius A* and estimate its speed and closest approach.
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astronomers → combine → speed
S301 is extremely faint, with the researchers describing it as a main-sequence star.
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researchers → describe → star
They estimate it has around 1.5 times the mass of the Sun and is about five times as bright.
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it → estimate → Sun
Its unusual orbit may also have an unusual origin.
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orbit → have → origin
Researchers suggest it could once have been part of a binary system that ventured too close to the black hole.
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that → suggest → hole
Sagittarius A* may have disrupted the pair, capturing S301 while sending its former companion flying away at enormous speed.
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companion → disrupt → speed
The star could help test Einstein's theory
The biggest scientific opportunity comes from S301's proximity to Sagittarius A*.
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opportunity → help → *
Einstein's general theory of relativity predicts that a rotating black hole can drag the fabric of spacetime around with it.
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hole → predict → it
This effect is known as frame dragging or Lense-Thirring precession.
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effect → know → dragging
The spinning black hole should gradually change the orientation of a nearby object's orbit.
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hole → spin → orbit
Because S301 travels so close to Sagittarius A*, astronomers may be able to detect these subtle changes by carefully tracking its position over time.
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astronomers → travel → time
If successful, the measurements could provide a direct way to determine the spin of the Milky Way's central black hole.
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measurements → provide → hole
That would offer an important test of general relativity in one of the most extreme environments accessible to astronomers.
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That → offer → astronomers
Scientists already know Sagittarius A*'s mass with considerable precision, but measuring its spin is much harder.
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measuring → know → spin
The next big opportunity comes in 2031
Astronomers plan to continue monitoring S301 with the upgraded GRAVITY+ instrument and eventually with the European Southern Observatory's Extremely Large Telescope.
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Astronomers → come → Telescope
The star's next close pass around Sagittarius A* is expected in 2031, giving researchers another valuable opportunity to measure its motion.
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pass → expect → motion
Comparing observations from multiple points in its orbit could reveal tiny changes that would otherwise be difficult to detect.
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that → compare → changes
The researchers published their findings in the journal Nature on August 19, 2026.
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researchers → publish → August
The discovery is important not simply because S301 has broken a stellar speed record, but because its extreme orbit turns the star into a natural laboratory for studying a supermassive black hole.
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orbit → break → hole
If scientists can detect the predicted orbital changes, S301 could help reveal how Sagittarius A* spins and provide a new test of Einstein's description of gravity.
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* → detect → gravity
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