Astronomers have shown that the powerful gravity at the center of the Milky Way can be reproduced without assuming a black hole sits there. Their new calculations suggest that an ultra-dense concentration of unseen matter might account for both the intense pull at the core and the way stars move across the wider galaxy.
Stars around the core
Decades of infrared tracking have mapped fast stars whipping around the Milky Way’s center, giving gravity a hard test. Using those star paths, Valentina Crespi at the Institute of Astrophysics in La Plata (IALP) in Argentina argued for a different central object.
Crespi’s team says a compact core of invisible particles can pull on nearby stars almost exactly the same way. That claim forces astronomers to hunt for subtle differences, because usual star motions may not reveal what the center is.
A dark matter core
At the center of their idea sits dark matter, material that adds gravity but emits no light. Instead of a black hole, the new analysis uses a packed core plus a wide, thinner halo. Gravity from the core controls the closest orbits, while the halo spreads mass across the galaxy’s larger disk.
Without a true point of no return, the model must still bend light and speed up gas enough to match older observations.
Orbits that still match
Close to Sgr A*, the compact object at our galaxy’s center, stars like S2 swing through space at extreme speed. After 16 years, astronomers tracked S2’s full loop and even saw a tiny orbital turn predicted by relativity.
Crespi’s model recreated S2’s path and also matched five dust-wrapped G objects that sweep farther out. Those orbits pin down the mass, but they do not say whether it is a black hole or a core.
A galaxy-wide slowdown
Far from Sgr A*, the Milky Way’s disk should slow as you move outward, but earlier models struggled to match details. A Milky Way rotation curve, a record of speed at many distances, shows a clear slowdown near the edge.
Gaia tracked more than a billion stars, and that motion map let researchers see where gravity starts acting like a point mass. Because Crespi’s halo carries mass outward, the same model could explain both the inner fast orbits and the outer slowdown.
What the image shows
In 2022, a new kind of evidence arrived when radio telescopes combined their signals to target Sgr A*. The Event Horizon Telescope, a global radio array that links telescopes, reported a bright ring around a darker center.
Light from hot gas bends around intense gravity, so a compact object can cast a shadow-like dip in brightness. Any replacement for a black hole must reproduce that ring-and-shadow pattern, or it fails against the image.
Hunting photon rings
Sharper images could reveal features that star tracking cannot, especially right at the edge of what gravity allows. One target is photon rings, narrow light loops that circle many times before escaping toward Earth.
A simulation showed that dense particle cores can still make a ring-like glow, yet they lack those extra loops. If future images find clean photon rings around Sgr A*, the dark core idea would face a serious problem.
Where the models split
Right now, the black hole and dark core pictures disagree only in places where gravity is strongest and hardest to measure. Crespi’s team built the core from fermions, tiny particles that resist squeezing into the same state, which changes the density profile.
In their fits, orbital predictions differed by less than 1 per cent, so current measurements blur the distinction. “More accurate data, particularly from stars closer to Sgr A*, is necessary to statistically distinguish between the models considered.” wrote Crespi.
Sharper measurements ahead
Next steps depend on measuring tiny position changes, not building a prettier picture of the galactic center. GRAVITY ties multiple telescopes together, and that combination sharpens starlight into much more precise position measurements.
“However, more precise S2 data sets, as obtained by the GRAVITY instrument, remain to be analysed in light of the fermionic models.” wrote Crespi. Fresh tracking of stars even closer than S2 would place the toughest limit on the dark core proposal.
Why the stakes grow
Accepting a dark core at Sgr A* would not just swap labels, it would change what astronomers expect to see near the center. Gas would orbit and heat in a gravity well without a black hole horizon, which could affect how bright flares rise and fade.
Particle physics would also matter, because a stable core demands dark matter that can pack tight without collapsing. If new observations reject the idea, the test still strengthens the black hole case by ruling out whole classes of look-alikes.
A testable alternative
Crespi’s proposal keeps the Milky Way’s best clues on the table, while treating the center and halo as one physical system. Either a photon-ring detection or sharper star tracking will decide the story, and that decision will also narrow what dark matter can be.
The study is published in Monthly Notices.
