Rosa Rubicondior: How Science Works - And Why Religion Doesn't - Testing Relativity In Extreme Conditions

Thursday, 27 August 2026

How Science Works - And Why Religion Doesn't - Testing Relativity In Extreme Conditions

A spinning black hole drags space-time around it, a phenomenon known as Lense-Thirring effect.

A star with an Extreme Orbit | Max Planck Institute for extraterrestrial Physics

One of the most striking differences between science and religion is that science does not merely offer explanations for what has already been observed. A scientific theory must also make precise predictions about phenomena that may not yet have been detected—and those predictions must expose the theory to the possibility of being proved wrong.

Einstein’s general theory of relativity is an outstanding example. More than a century after it was formulated, astronomers are still finding new ways to test its predictions under conditions far more extreme than anything available to Einstein. The latest opportunity is provided by a faint star named S301, racing around Sagittarius A*, the supermassive black hole at the centre of the Milky Way.

According to a new paper by the GRAVITY+ Collaboration, published in Nature, S301 follows an extraordinarily elongated orbit around the black hole, completing one revolution every 8.7 years—the shortest orbital period yet measured for any star around Sagittarius A*. At its closest approach, it passes only about 1.78 billion kilometres from the black hole, roughly twelve times the distance between Earth and the Sun. There it reaches approximately 25,000 kilometres per second, or more than eight per cent of the speed of light, making it the fastest-known star in the Milky Way.

S301 is not travelling through ordinary space governed adequately by Newtonian gravity. It is plunging deep into the gravitational field of an object containing about 4.3 million times the mass of the Sun. Its orbit therefore acts as a natural probe carried into a region of severely curved spacetime that no human-made spacecraft could approach and survive.

General relativity predicts that an orbit in such a field will not form a perfectly closed ellipse. The point of closest approach shifts with each revolution, producing what is known as Schwarzschild precession—an effect already detected in the orbit of the better-known star S2. S301 approaches Sagittarius A* about ten times more closely than S2 in terms of the black hole’s Schwarzschild radius, so the relativistic effects on its motion should be considerably stronger.

More tantalisingly, if Sagittarius A* is rotating, Einstein’s theory predicts that it should drag the surrounding spacetime around with it. This much weaker phenomenon, known as the Lense–Thirring effect or frame-dragging, should produce an additional small change in S301’s orbit. By monitoring the star with the GRAVITY+ instrument on the European Southern Observatory’s Very Large Telescope Interferometer and obtaining future spectroscopic measurements with MICADO on the Extremely Large Telescope, astronomers hope to measure the black hole’s spin within about a decade.

It is important, however, not to describe that hoped-for measurement as an accomplished result. The observations already reveal strong relativistic orbital precession consistent with general relativity, and S301’s orbit is sensitive enough to the black hole’s rotation for frame-dragging potentially to become measurable. The spin of Sagittarius A* has not yet been determined from the star’s motion. The researchers still lack the radial-velocity measurements needed to reconstruct its complete three-dimensional orbit, and the next close passage is expected in 2031.

That distinction illustrates how science progresses. Astronomers do not announce that Einstein must be right and reinterpret whatever happens accordingly. They calculate how large the predicted effect should be, identify the observations needed to detect it, estimate the uncertainties and then wait for nature to supply the verdict. If S301 behaves as predicted, general relativity will have passed another demanding test. If it does not, the discrepancy will demand an explanation and might point towards incomplete modelling, an unseen influence or new physics.

Creationist cosmology offers nothing remotely comparable. No reading of Genesis predicts an 8.7-year stellar orbit, a speed of 25,000 kilometres per second, relativistic pericentre advance or the measurable dragging of spacetime by a rotating black hole. There are no creationist equations from which these quantities can be calculated and no conceivable observation that would cause believers to abandon their predetermined conclusion. Ancient mythology begins with an answer and is insulated from testing; science makes itself vulnerable by stating in advance what the evidence should show.

S301 is therefore more than an astronomical curiosity or a new galactic speed record. It is a naturally occurring experiment in fundamental physics, taking place around the Milky Way’s central black hole. Its value lies precisely in the fact that the outcome has not been declared in advance. Over the coming years, an almost invisible star will either follow the path predicted for it through rotating, curved spacetime—or present physicists with something new to explain.

Where Does Frame-Dragging Come From? Einstein’s general theory of relativity describes gravity not as a conventional force but as the curvature of spacetime produced by mass and energy. A non-rotating spherical body produces one pattern of curvature; if the body rotates, its angular momentum produces an additional distortion. The rotating body effectively pulls local inertial frames around in the direction of its rotation.

This phenomenon is called the Lense–Thirring effect, after the Austrian physicists Josef Lense and Hans Thirring, who derived it from general relativity in 1918. It is also known as frame-dragging. The name does not imply that spacetime is a material substance being stirred. It means that the paths of freely moving objects—and even the orientation of ideal gyroscopes—are altered by the rotating gravitational field.

Why does a collapsing star not rotate infinitely fast?

The familiar comparison with a spinning ice skater has limits. As a massive star contracts, its rotation does accelerate because angular momentum must be conserved. However, the star cannot continue behaving as a rigid sphere while its radius falls towards zero. Magnetic fields, turbulence and differential rotation redistribute its angular momentum, while expelled matter, electromagnetic radiation and gravitational waves can carry some of it away.

Once a black hole forms, it has no solid surface rotating through space. Its remaining angular momentum is instead encoded in the geometry of the surrounding spacetime. A rotating black hole is described by the Kerr solution of general relativity and is assigned a dimensionless spin:
\[\small \chi=\frac{cJ}{GM^2},\]
where \(\small J\) is its angular momentum and \(\small M\) its mass. For a Kerr black hole, \(\small\chi\) cannot exceed 1. A collapsing object with too much angular momentum must redistribute or shed some of it before it can settle into a black hole with an event horizon.

The singularity should therefore not be imagined as an infinitesimally small material ball with a surface moving infinitely fast. In the classical description of a rotating black hole, the singularity is ring-shaped rather than point-like—and general relativity itself is expected to become inadequate under such extreme conditions. Whatever replaces the singularity in a quantum theory of gravity, there is no material surface to which an ordinary rotational speed can be assigned.

How does frame-dragging affect an orbit?

Around a rotating black hole, frame-dragging causes the orientation of an orbit to change gradually. This is distinct from Schwarzschild precession, which results from spacetime curvature caused by the black hole’s mass alone. Lense–Thirring precession is much weaker and diminishes rapidly with distance, making it exceptionally difficult to measure.

S301 passes close enough to Sagittarius A* for its orbit potentially to reveal this additional precession. Continued observations may therefore show how rapidly the black hole is rotating by measuring how its angular momentum twists the spacetime through which the star travels. That measurement has not yet been made: S301 is a newly discovered opportunity to detect the effect, not yet a confirmed detection of it.

The paper in Nature was accompanied by a detailed explanation in a news release from the Max Planck Institute for Extraterrestrial Physics:

A star with an Extreme Orbit
A star with an Extreme Orbit

To the point:

Discovery S301: Researchers at the Max Planck Institute for Extraterrestrial Physics found the star S301, which orbits the Milky Way's central black hole Sagittarius A* (Sgr A*) closer and faster than any known star, with an 8.7-year orbit and closest approach similar to the Sun-Saturn distance.
Observation Challenges: S301 is extremely faint—two billion times dimmer than Betelgeuse—making detection difficult; advanced instruments like GRAVITY and new data analysis methods enabled precise tracking of its position near Sgr A*.
Scientific Importance: S301 probes spacetime closer to the black hole than previous stars, allowing researchers to study the black hole's spin and test fundamental physics theories such as the Kerr metric and the no-hair theorem.
Technological Advances: The use of GRAVITY at the Very Large Telescope Interferometer and future MICADO instrument at the ESO Extremely Large Telescope provides unprecedented resolution and sensitivity to study stars near the galactic center.

A team from the Infrared/Submillimetre Astronomy Group at the Max Planck Institute for Extraterrestrial Physics (MPE) has discovered a new star that comes closer to the supermassive black hole Sagittarius A* (Sgr A*) at the heart of our Milky Way than any other known star. The newly identified object, named S301, swirls around the black hole in a highly elliptical orbit with a period of approximately 8.7 years. At its closest approach, it comes within just over twelve astronomical units of Sagittarius A*, roughly the distance between the Sun and Saturn. As a result, S301 is now the star with the shortest known orbital period and the tightest orbit ever observed in the galactic centre.

Even more importantly, S301 moves through a region where the black hole’s rotation drags spacetime itself, a phenomenon that only occurs in the immediate vicinity of a massive, spinning object.

S301 probes spacetime in the Galactic Center ten times closer to Sagittarius A* than our previous best star, S2,. Within the next decade, we will measure the black hole’s rotation directly — a milestone for general relativity.

Professor Dr Reinhard Genzel, co-author.
Director at MPE and Nobel Laureate for Physics in 2020.
Max Planck Institute for Extraterrestrial Physics
Garching, Germany

An almost invisible star: a flicker in a sea of light

S301 is two billion times fainter than Betelgeuse, one of the brightest stars in Orion. Its light is so soft that even in the best images of the Galactic Center it appears as no more than a tiny point, lost among numerous, much brighter stars.

S301 was first identified in spring 2023 using the GRAVITY instrument at the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) in Chile. Developed through an international consortium led by MPE, GRAVITY combines the light collected by four 8-metre telescopes, achieving an angular resolution 40 times sharper than that of a single telescope. The recently completed upgrade to GRAVITY+ , which includes a new adaptive optics system and laser guide stars, has increased the instrument’s sensitivity by a factor of 10 to 100. This unprecedented combination of precision and sensitivity has made it possible to detect S301, a new and extremely faint star.

GRAVITY’s exceptional resolution makes it possible to observe stars at the center of the Milky Way on scales comparable to the size of our solar system, even when they are extremely faint. The discovery of S301 is the result of four decades of systematic observations by the MPE team. Over this period, the team has mapped the region around Sagittarius A* with steadily increasing precision, measuring the stars’ motions and characterising the mass concentrated at the centre of the Galaxy.

Two relativistic effects: one large, one tiny

The orbit of S301 deviates significantly from an ellipse, the path predicted by Newton’s classical theory of gravitation. This is a clear sign of relativistic effects that occur only in the vicinity of a massive, rotating black hole. Two phenomena are at play:

Schwarzschild Precession: If space is curved around a central mass – such as, in this case, the supermassive black hole – this affects the orbits of the objects in its vicinity. The gradual shift in the orbit’s closest approach point, known as pericentre advance, was previously observed in the star S2. It arises from the curvature of spacetime caused by the black hole’s mass. The Schwarzschild solution of general relativity remains a useful approximation to explain the orbit of S2, even for a spinning black hole at the center of the Galaxy.
Lense-Thirring-Effect (Frame-Dragging-Effect): As the black hole at the centre of our Milky Way is not only extremely massive but also rotates, another relativistic effect occurs alongside Schwarzschild precession: the Lense–Thirring effect. A rotating mass, in a sense, drags the surrounding space-time along with it – much like a rotating spoon setting the water in a cup in motion. The effect is significantly weaker and therefore more difficult to detect. S301 is now the first star in which this effect around a black hole has been measured.

Animation of the Lense-Thirring-Effect
This animation shows how a spinning black hole drags space-time around it, a phenomenon known as Lense-Thirring effect. If a star gets close enough to a spinning black hole, its orbit will change in a way that can be measured over long timescales with sufficiently precise telescopes and instruments.
© ESO/M. Kornmesser

S301 is the first star to orbit directly in the region around Sagittarius A* where the frame-dragging effect is extreme. We’re not just measuring spacetime curvature; we are measuring how it gets distorted by the rotation of the black hole itself. That is unique.

Felix Mang, corresponding author.
Max Planck Institute for Extraterrestrial Physics
Garching, Germany.

Why is the measurement so challenging?

Tracking such a star is a technical triumph. To measure S301’s orbit, the Scientists analysed years of observational data, recorded at a resolution of just a few milliarcseconds — equivalent to the size of a car on the Moon. The star’s position was monitored across numerous observations over many years.

Until now, detecting such a faint object had been impossible, largely because of the extreme contrast in brightness between S301 and the stars orbiting the black hole. Using a new data-analysis method, a team at MPE has now succeeded in extracting the faint signal. It is like trying to hear the buzz of a fly while a symphony orchestra is playing.

Interviewfilm with Reinhard Genzel, Frank Eisenhauer and Stefan Gillessen
In this video, Frank Eisenhauer, Reinhard Genzel and Stefan Gillessen explain how the newly discovered star S301 could, for the first time, enable a measurement of the rotation of the supermassive black hole at the centre of the Milky Way.
© MPE

The star’s advantage: faster, more precise and sensitive to Sagittarius A*’s spin

A key advantage of S301 over observing the diffuse hot gas around black holes (such as the one imaged in M87 by the Event Horizon Telescope) is that we can directly observe motion. Combining the position measurements from GRAVITY+ and radial velocity data from MICADO on the future Extremely Large Telescope of ESO, will allow the team to accurately reconstruct the star’s three-dimensional motion and for the first time, directly determine the spin of Sagittarius A*.
We’re faster, more precise, and more direct. With S301, we’re measuring the rotating spacetime itself, not indirectly through an image, but directly through the motion of a single star.

Professor Dr Reinhard Genzel

Animation of all known stars in the GC orbiting the central massive black hole Sgr A*
Animation of all known stars in the Galactic Center orbiting 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.
© MPE

Dreams of the Future: Do black holes really have no hair?

The observation of S301 is part of a long-term vision: testing the Kerr metric, the mathematical description of spacetime around a rotating black hole:

In the long run, the analysis of S301’s orbit could even provide evidence for the no-hair theorem, the statement that a black hole is fully described by just three properties: mass, angular momentum, and electric charge.

Stefan Gillessen, corresponding author
Max Planck Institute for Extraterrestrial Physics
Garching, Germany.

The chance to discover the beauty of nature in the form of this star is truly a dream come true, and with GRAVITY+ and the upcoming MICADO instrument, currently being developed in an international consortium led by MPE for the ESO Extremely Large Telescope: to explore strange new worlds, seek out new physics, and see what nobody has seen before.

Frank Eisenhauer, co-author
Max Planck Institute for Extraterrestrial Physics
Garching, Germany.

Stars orbiting the central massive black hole Sgr A* in the center of our galaxy
Stars orbiting the central massive black hole Sgr A* in the center of our galaxy, the Milky Way. The newly discovered star S301 (orange orbit) approaches Sgr A* closer than any other star. This will allow us to measure how fast Sgr A* is rotating within the next ten years.

© MPE

Background
The Max Planck Institute for Extraterrestrial Physics (MPE) investigates physical processes in the Universe. It is particularly renowned for proving that Sagittarius A* (Sgr A*) is a supermassive black hole — a discovery that earned MPE Director Reinhard Genzel the Nobel Prize in Physics in 2020. The VLTI instrument GRAVITY and its upgrade to GRAVITY+ was built by a consortium led by MPE in close collaboration with institutions from Belgium, France, Germany, Ireland, Mexico, Portugal, and the UK. GRAVITY+ received significant funding from the Max Planck Foundation.

Beginning of November 2025, four lasers were fired into the sky above ESO’s Paranal Observatory in Chile, each creating an artificial star to help astronomers measure and correct atmospheric blur. This impressive launch, one from each 8-meter telescope, marks a key milestone of the GRAVITY+ project, led by MPE, significantly enhancing the VLTI’s ability to observe fainter objects and cover more of the southern sky.

The European Southern Observatory (ESO) is an intergovernmental organisation supported by 16 member states and two associated countries. It develops, builds and operates leading ground-based observatories – with its headquarters in Germany and three sites in Chile. ESO enables researchers worldwide to investigate ground-breaking astronomical questions and to promote public interest in astronomy.
Publication:
Abd El Dayem, K., Abuter, R., Aimar, N. et al.
Discovery of a star sensitive to the spin of Sagittarius A*.
Nature (2026). https://doi.org/10.1038/s41586-026-10894-w

Abstract
Residing in the centre of the Milky Way, Sagittarius A* (Sgr A*) is the closest massive black hole¹ (MBH). Its vicinity has allowed measuring individual stellar orbits around it^2,3,4. The stars act as test particles and probe the gravitational potential around the \(\small 4.3 \times 10^6M_⊙\) MBH. These observations have determined the central mass to sub-per-cent precision⁵, and the mildly relativistic motions of stars have given access to the dominant relativistic corrections, the gravitational redshift^6,7, the transverse Doppler effect and the prograde precession imposed by the Schwarzschild metric nature of the potential⁸. These effects are of order \(\small β^2 = \left( v/c \right) ^2\) (for velocity \(\small v\) and speed of light \(\small c\)). The Kerr metric for a rotating black hole leads to corrections of order \(\small β^3\). Here, we report the discovery of a faint main-sequence star (\(\small m_K = 19.3\)), S301, on an 8.7-year orbit and with small enough a pericentre distance, such that the peak velocity of the star reaches 25,000 km s⁻¹. Within the measurement abilities of current near-infrared interferometry and future spectroscopy on an extremely large telescope, the motion of S301 is directly sensitive to the spin of Sgr A*. The high eccentricity of S301 suggests that it is the captured component of a binary that was torn apart by the Hills mechanism.

Abd El Dayem, K., Abuter, R., Aimar, N. et al.
Discovery of a star sensitive to the spin of Sagittarius A*.
Nature (2026). https://doi.org/10.1038/s41586-026-10894-w

Copyright: © 2026 The authors.
Published by Springer Nature Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

S301 has not yet supplied a measurement of Sagittarius A*’s spin, and that is precisely what makes it scientifically interesting. General relativity predicts how a rotating black hole should alter the star’s orbit, astronomers have identified the observations required to detect that alteration, and improved instruments should eventually reveal whether nature behaves as predicted. The conclusion remains conditional upon evidence that has still to be collected.

This is science operating as it should: cautious about what has already been established, explicit about what remains uncertain and willing to risk a cherished theory against future observation. If the predicted frame-dragging is detected, general relativity will have survived another exceptionally severe test. If it is absent or differs significantly from the calculated effect, physicists will have a genuine problem to investigate rather than an inconvenient fact to explain away.

Creationist cosmology contributes nothing to this undertaking. No creation myth predicts the existence, mass or rotation of Sagittarius A*; the speed and orbit of S301; Schwarzschild precession; or the Lense–Thirring effect. Nor can it specify any observation that would show its supernatural explanation to be wrong. Whatever astronomers discover can simply be declared to be how a creator chose to make things, allowing the belief to accommodate every possible result while successfully predicting none of them.

The contrast could scarcely be clearer. Ancient religious narratives begin with an untouchable conclusion and bend every observation around it. Science begins with evidence, constructs a mathematical explanation and then asks nature for permission to retain it. S301 is not circling an article of faith; it is circling a testable prediction.

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