This Star Orbits Our Galaxy's Heart at a Record-Breaking Speed—and Could Help Uncover Secrets About the Behemoth Black Hole There

A star racing through the Milky Way’s inner reaches may offer astronomers an unusually close look at the galaxy’s central black hole. Known as S301, the object can reach about 56 million miles an hour—roughly 8 percent of light speed—as it follows an orbit around Sagittarius A*. Its path brings it nearer to that black hole than the routes of other known stars in a way that could make a long-sought measurement possible. The discovery focuses attention on a fundamental unresolved question: whether the immense object at the Milky Way’s core is rotating.

Sagittarius A* lies at the center of the Milky Way, around 27,000 light-years from Earth. It is a supermassive black hole, and stars near the galactic center move under its powerful influence. Researchers have suspected for years that the black hole rotates, but that expectation has not yet been confirmed by a direct observation. The question has remained open even as astronomers have watched stars move around the galaxy’s heart.

The newly identified star changes the prospects for testing that idea. During its nearest passes, S301 is expected to move through a region where the black hole’s rotation should leave an observable imprint on its orbit. By tracking those changes carefully, scientists could determine whether Sagittarius A* is spinning and, if it is, measure that motion directly for the first time.

What distinguishes S301 is not simply its extreme velocity. Other stars circle the Milky Way’s central black hole as well, but its exceptionally tight approach is thought to place it alone among known objects in the position needed to sense the proposed rotational effects. A visual representation of the orbit marks S301’s route in red, underscoring its special proximity to the central object. In that respect, the star’s value lies in where its journey takes it as much as in how fast it travels.

The result, published August 19 in Nature, turns a fast-moving star into a possible instrument for investigating a black hole from afar. Rather than sending a probe toward the galactic center, researchers can use repeated observations of S301’s motion to look for the subtle influence expected from the black hole’s behavior. The star provides a moving reference point in a region that cannot be reached directly.

That makes the finding important beyond the identification of another stellar orbit. The center of the Milky Way contains the black hole at the galaxy’s core. A direct measurement of its rotation would add a new piece of evidence about one of the most influential objects in Earth’s home galaxy. It would also convert a longstanding expectation about Sagittarius A* into an observation that can be tested against the star’s path.

The opportunity also illustrates how astronomy can advance through precise maps of motion. S301’s speed is extraordinary on an everyday scale, but the most useful feature for this work is the timing and shape of its close passages. Each return toward Sagittarius A* could provide another chance to compare the star’s observed trajectory with the effects expected if the black hole is rotating.

For now, the study identifies a promising test rather than announcing a settled answer about the black hole’s spin. The proposed measurement depends on observing S301 closely enough during its closest approaches to separate a rotational signal from the broader gravitational conditions around the galactic center. The next observations will therefore be central to deciding whether the anticipated effect can be detected.

Stefan Gillessen, an astronomer at Germany’s Max Planck Institute for Extraterrestrial Physics and a co-author of the study, told Science News that the team is excited by the star’s scientific promise. If S301 performs as hoped, its rapid circuit could help resolve a question that has remained open despite decades of interest in Sagittarius A*: whether the Milky Way’s central black hole is truly in rotation.

Source: Smithsonian Magazine