Fastest Star Astronomers Spot Record-Breaking S301 Orbiting the Milky Way’s Monster Black Hole

Astronomers have identified what is now the fastest known star in the Milky Way, and it is moving through one of the most extreme gravitational environments in the galaxy. Named S301, the faint star is orbiting Sagittarius A* — the supermassive black hole at the centre of our galaxy — at speeds reaching roughly 25,000 kilometres per second, or more than 8% of the speed of light.

The discovery is remarkable not simply because of the star’s extraordinary velocity. S301 also passes closer to Sagittarius A* than any other known star, giving astronomers an unusual opportunity to study how gravity behaves around a rotating supermassive black hole.

The findings were reported in Nature by an international research team using observations from the European Southern Observatory’s Very Large Telescope Interferometer and its GRAVITY instrument.

A Star Moving at 25,000 Kilometres Per Second

S301 is travelling at an astonishing maximum speed of approximately 25,000 km/s. That is around 90 million kilometres per hour and more than 100,000 times the speed of a commercial aircraft.

To put that into perspective, light travels at approximately 300,000 km/s. S301 therefore reaches roughly 8% of the speed of light during its closest approach to Sagittarius A*.

But S301 is not simply racing in a straight line through space.

It follows an extremely elongated, highly eccentric orbit around Sagittarius A*. The star takes approximately 8.7 years to complete one revolution, accelerating dramatically as it approaches the black hole and slowing as it travels toward the far end of its orbit.

That extreme orbital shape is one of the reasons the star is so scientifically valuable.

How Close Does S301 Get to Sagittarius A*?

The most extraordinary aspect of S301 may actually be its distance from the black hole.

At its closest approach, the star comes to roughly 12 times the Earth-Sun distance, or around 12 astronomical units. That is approximately comparable to the distance between the Sun and Saturn.

For an object orbiting a black hole with a mass of roughly 4.3 million Suns, this is an exceptionally close encounter.

S301’s orbit is about ten times closer to Sagittarius A* at its closest point than the orbit of the famous S2 star, which has previously been one of the most important objects for testing gravity around the Milky Way’s central black hole.

Yet S301 is not falling directly into the black hole.

Its velocity and orbital motion allow it to remain gravitationally bound, repeatedly swinging around Sagittarius A* before travelling back outward.

Why Doesn’t the Black Hole Simply Swallow It?

A common misconception is that anything approaching a black hole must inevitably be consumed.

That is not how orbital mechanics works.

If an object has sufficient sideways velocity, it can remain in orbit around a black hole in much the same way that planets orbit the Sun. The crucial difference is that the gravitational environment near a black hole becomes much more extreme.

S301’s highly elongated orbit means it spends most of its time farther away from Sagittarius A*, while its speed rises dramatically near its closest approach.

Astronomers can therefore observe how the star responds to the black hole’s gravitational field without the star crossing the event horizon.

This makes S301 a natural test particle for extreme gravity.

A Natural Laboratory for Einstein’s Theory

The real scientific importance of S301 goes far beyond breaking a speed record.

Its orbit could provide a new way to test Einstein’s general theory of relativity.

According to general relativity, massive objects do not simply exert a conventional gravitational force. They distort spacetime itself. Around a rotating black hole, that distortion becomes even more complicated.

A rotating black hole is predicted to drag spacetime around with it — an effect known as frame dragging, or Lense-Thirring precession.

S301 is particularly interesting because its orbit comes close enough to Sagittarius A* for the effects associated with the black hole’s rotation to potentially become measurable.

The research team says S301’s motion could eventually allow scientists to constrain the spin of Sagittarius A*, something that has not yet been directly measured for this quiet supermassive black hole.

Watching Spacetime Bend

The most fascinating part of the discovery is that astronomers are effectively using a star as a probe of invisible physics.

Scientists cannot see a black hole directly in ordinary light because light cannot escape from inside its event horizon. Instead, they study its influence on surrounding matter and objects.

Stars such as S301 provide another method.

By repeatedly measuring the star’s position and velocity, researchers can reconstruct its orbit with extraordinary precision. If the orbit deviates from the path predicted by simpler gravitational models, those deviations can reveal relativistic effects.

The research team notes that conventional effects such as gravitational redshift and relativistic orbital precession have already been observed in stars around Sagittarius A*. S301 moves into a regime where higher-order effects associated with the Kerr description of a rotating black hole become increasingly relevant.

That means the star could eventually help scientists determine whether the black hole’s rotation is producing the predicted distortion of spacetime.

The Technology Behind the Discovery

Finding S301 was not simply a matter of pointing a telescope at the centre of the Milky Way.

The galactic centre is extremely difficult to observe. Dense clouds of dust obscure visible light, while numerous stars appear crowded together in a very small region of the sky.

S301 itself is faint, making the challenge even greater.

Astronomers used the GRAVITY instrument at the European Southern Observatory’s Very Large Telescope Interferometer in Chile. By combining light collected by multiple telescopes, interferometry allows astronomers to achieve extremely precise measurements of stellar positions.

Researchers tracked S301’s motion using observations extending back to 2017 and combined those measurements with earlier information to reconstruct its orbit.

This is an important reminder that major astronomical discoveries often depend not on a single observation, but on years of extremely precise measurements.

S301 May Have an Extraordinary Origin

The star’s unusual orbit also raises questions about where it came from.

Researchers suggest S301 may be the captured remnant of a binary star system that interacted with Sagittarius A*. In a process known as the Hills mechanism, the black hole can disrupt a binary system: one star may be thrown outward at enormous velocity while the other becomes tightly bound to the black hole.

If this interpretation is correct, S301 could be the surviving member of a stellar system that was radically reshaped by the gravity of the Milky Way’s central black hole.

That possibility makes the star valuable not only for studying relativity, but also for understanding the dynamic history of the galactic centre.

The Next Decade Could Be Even More Important

The discovery is only the beginning.

Researchers plan to continue monitoring S301’s orbit. Future observations, including spectroscopy with extremely large telescopes, could provide additional information about the star’s motion and allow scientists to search for subtle relativistic effects with greater precision.

The next decade could therefore turn S301 into one of the most important natural laboratories for testing strong-field gravity.

Instead of building a spacecraft capable of approaching a black hole, astronomers have something much better available to them: nature has already placed a star on an extreme orbit around one.

A Speed Record That Could Become a Physics Experiment

S301’s record-breaking velocity is spectacular, but its true importance lies elsewhere.

The star is travelling through a region where gravity becomes powerful enough for subtle predictions of general relativity to become observable. Its highly eccentric orbit brings it close to Sagittarius A*, while its repeated passages allow astronomers to measure how the path evolves over time.

Every tiny change in that orbit could contain information about the black hole.

If future measurements detect the predicted signatures of frame dragging, scientists could gain the first direct observational handle on the spin of the Milky Way’s central supermassive black hole.

In that sense, S301 is more than the fastest star ever observed in the Milky Way.

It may become a cosmic instrument — a naturally occurring probe travelling through some of the most extreme spacetime in our galaxy.

And at 25,000 kilometres per second, it is carrying that experiment at a speed that brings Einstein’s universe into extraordinary focus.