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What if the “monster” at our galaxy’s center isn’t a black hole at all?
Welcome back to FreeAstroScience.com—our home for clear science, told like a human story, for you.
Stay with us to the end, and you’ll see what this new idea explains, and what could break it.
As we write this, we’re thinking about two kinds of gravity. One pulls on stars. The other pulls on our emotions, when the universe feels too big.
And yes—some of us read and work from a wheelchair. That doesn’t shrink our universe. It changes our angle, and sometimes the angle changes everything.
What are astronomers trying to explain at Sagittarius A*?
Astronomers track stars close to Sagittarius A* (Sgr A*) using near-infrared light, which cuts through central dust. For decades, many studies have treated Sgr A* as a supermassive black hole candidate. From long-term monitoring, one estimate places the Sun’s distance at about 8.277 kpc and the central mass at about (4.297 \times 10^6) solar masses.
One star matters a lot here: S2. S2 completes an orbit in about 16 years, with eccentricity around 0.88. Teams measured relativistic effects in S2’s motion, including gravitational redshift and Schwarzschild precession around 12 arcminutes per revolution.
Press coverage also highlights the “violent” speeds near the center, up to a few thousand kilometers per second for the S-stars. Near Sgr A*, astronomers also track dust-enshrouded objects called G-sources (or G-objects).
The big challenge is that one gravity model should explain the inner orbits and the outer Milky Way rotation pattern.
How can dark matter imitate a black hole?
The new proposal says: keep gravity and General Relativity, but change the central object.
Crespi and colleagues study a “horizon-less” supermassive compact object made of self-gravitating fermionic dark matter.
In this picture, the same dark matter distribution forms a super-dense core and a much more spread-out halo. [
That “core–halo” shape matters. The dense core can mimic the gravitational pull of a black hole closely enough to match measured relativistic effects on S2’s orbit, according to the paper’s framing.
The outer halo, in the same continuous model, can reproduce the Milky Way rotation curve as seen in the latest Gaia DR3 rotation-curve data.
Gaia DR3 is central to the story told in the research highlight. The RAS highlight says Gaia DR3 shows a slowdown in the outer rotation curve—a “Keplerian decline.”
The same highlight argues the fermionic model’s outer halo can explain that decline when combined with ordinary matter components (disc and bulge).
A small formula, in plain sight
The paper discusses particle kinetic energy in a relativistic form.
That’s not a “magic spell.”
It’s just a compact way to say: near the center, speeds get high, so relativity matters.
What does the new MNRAS paper actually find?
Crespi et al. (MNRAS, February 2026) compare black-hole and fermionic-dark-matter scenarios using astrometric data from S2 and five G-sources. phys They explore different fermion masses, including 56 keV (lower core compactness) and 300 keV (higher core compactness).
They sample parameter space with Markov Chain Monte Carlo and compare models using Bayes factors when the likelihood function matches.
For their selected S2 dataset, they report the 56 keV model is slightly favored over the 300 keV model.
For the G-objects, the abstract says no conclusive preference appears between models.
They also report that, for all stellar objects tested, the black hole and fermionic models predict orbital parameters that differ by less than 1%.
That last line lands like a plot twist.
If two different “engines” predict almost the same orbits, today’s data can’t easily pick the winner.
The RAS highlight says the dark matter model still offers one selling point: a single framework spanning central stars, shadow-like imaging claims, and galaxy-wide rotation.
Key facts you can scan fast
| What we measure | Concrete detail | What the fermionic model claims |
|---|---|---|
| Distance and mass used for Sgr A* | ~8.277 kpc and ~4.297×106 M☉ [page:1] | A horizon-less fermionic core can fit S2-like relativistic effects within one core–halo solution [page:1] |
| S2 orbit basics | Period ~16 years; eccentricity ~0.88 [page:1] | BH and fermionic models give orbital parameters differing by <1% for tested objects [page:1] |
| Relativistic precession of S2 | Schwarzschild precession ~12 arcmin per revolution [page:1] | The paper describes fermionic cores reproducing relativistic effects measured for S2 [page:1] |
| Outer Milky Way rotation | Gaia DR3 rotation curve shows a slowdown (“Keplerian decline”) [page:2] | Outer halo in the same fermionic distribution can account for that pattern (with disc and bulge) |
A table like this is our “train scroll” tool.
You can read it between two stops.
What could prove it right—or wrong?
The RAS highlight is blunt: current inner-star data can’t decisively separate the two scenarios yet.
Crespi et al. echo that: they say we need more accurate data, especially from stars closer to Sgr A*, to distinguish the models statistically.
They also point to improved S2 datasets from the GRAVITY instrument as a next step for testing the fermionic models. phys
On the imaging side, the research highlight says a 2024 MNRAS study (Pelle et al.) found illuminated dark matter cores can cast a shadow-like feature similar to the EHT image of Sgr A*.
That same highlight says photon rings would be a key signature for black holes and absent in the dark matter core scenario. It also names GRAVITY on the Very Large Telescope in Chile as one instrument that can sharpen this test.
So the “path to proof” looks like this. Measure tighter orbits with higher precision, then search for features that only one model predicts. If the data keeps matching both, nature is asking us for better questions. sci
Why this matters for how we think
This isn’t just a debate over one object. It’s a test of whether one dark matter framework can connect the galaxy’s heart to its far outskirts. That “unified framework” idea is stated plainly in the RAS highlight, and it’s the emotional hook too: one story, one gravity, one galaxy.
At FreeAstroScience.com, we write this for you on purpose. We want you to feel included, not lectured.
We also want you to keep your mind switched on—always.
We repeat a warning we live by: the sleep of reason breeds monsters. Sometimes that monster is a bad headline. Sometimes it’s our own fear of not understanding.
Sources
- Royal Astronomical Society (RAS), “Dark matter, not a black hole, could power Milky Way’s heart” (4 Feb 2026): https://ras.ac.uk/news-and-press/research-highlights/dark-matter-not-black-hole-could-power-milky-ways-heart
- Crespi, V. et al., Monthly Notices of the Royal Astronomical Society (Feb 2026), “The dynamics of S-stars and G-sources orbiting a supermassive compact object made of fermionic dark matter” (DOI: 10.1093/mnras/staf1854): https://academic.oup.com/mnras/article/546/1/staf1854/8431112?login=false
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