Science advances, and this also means rewriting what we believed to be ‘absolute truth’ within different fields of knowledge. For example, for decades the scientific consensus has been unwavering in pointing out that in the heart of the Milky Way, about 27,000 light years from Earth, there is a huge supermassive black hole. But now this is not so clear thanks to a new study who has “seen” something even more interesting in this location.
Breaking rules. It has been a study published this year the one who has proposed that the “monster” that governs our galaxy is not a black hole, but an ultradense core of dark matter. A compact object of almost four million solar masses that a priori would be composed entirely of fermionic dark matter.
How do they know it? To support this bold claim, researchers have used the RAR model. This is very important, since, unlike the classical theory, which separates the central black hole from the halo of dark matter that surrounds the galaxy, this new approach unifies both concepts into one.
In this way, it is proposed that dark matter particles are highly concentrated in the galactic center, forming a compact and massive nucleus, while on the outskirts they are diluted, forming the well-known and extensive dark halo.
The big question. If it’s not a black hole, why does it “look” like one? And it is something normal that passes through our minds, especially after the year 2022 when the Event Horizon Telescope (EHT) gave us the first “photograph” of Sgr A* where a bright ring could be seen surrounding a deep central darkness. And although this could be definitive proof that there is a black hole at the center of our galaxy, this is not the case.
This is where previous key work published in 2024 comes into play, which pointed out that a dense core of fermions illuminated by an accretion disk generates a “shadow” visually indistinguishable from that cast by a classical black hole. That is, this dark matter is disguised to be able to deceive our telescopes when taking different measurements.
Mathematical tests. In addition to this interesting theory, the scientific team has subjected it to a rigorous statistical examination using complex simulations and Bayesian analyzes to verify its robustness. Here they have shown that this dark matter core perfectly explains, for example, the orbits of the S stars that orbit the galactic center.
But this unified model also fits precisely with the most recent data on the galaxy’s outer rotation curve provided by the Gaia DR3 mission.
You have to look better. Although the mathematics add up and the model passes the statistical tests with flying colors, dethroning a supermassive black hole from the scientific imagination is not an easy task. And it is somewhat relevant, since the dark matter core lacks an event horizon, which is the absolute gravitational boundary of no return from which any element would be absorbed by the black hole.
To know once and for all whether we are dealing with a black hole or a giant ball of dark matter, astronomers are aiming for the next generation of observations. We need to track what happens a little closer to the absolute center and future data of the GRAVITY interferometer (installed on the Very Large Telescope) will be key to detecting the subtle orbital deviations in the closest stars that would end the debate.
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