There’s a huge mystery at the center of our Milky Way galaxy. Traditionally, experts say it’s a supermassive black hole, weighing in at about 4 million times the mass of the Sun. But a new study raises an exciting alternative: what if it’s not a black hole at all, but a giant blob of dark matter?
Carlos Argüelles, an astrophysicist from Argentina, suggests that this idea might not be that far-fetched. He points out that if we look closely, there’s evidence to support this dark matter theory, too. Dark matter is already known to make up about 84 percent of the universe. It’s elusive and doesn’t emit or absorb light, but we can see its effects through gravity.
Recently, scientists have traced the paths of stars near the galactic center using their movements to infer the mass at the heart of the Milky Way. The most straightforward explanation? A supermassive black hole called Sagittarius A (Sgr A). Images taken by the Event Horizon Telescope in 2022 even showed a shadow believed to be cast by this black hole.
However, recent research indicates that a dense concentration of dark matter could also create a similar shadow. An international team, led by Valentina Crespi, has explored this idea further, investigating whether the gravitational effects on orbiting stars could be due to dark matter instead of a black hole.
One interesting candidate is “fermionic dark matter.” This type of dark matter acts like a dense blob, akin to a neutron star. It has unique properties that prevent it from condensing infinitely, unlike other dark matter theories, which describe it as more diffuse.
When Crespi’s team studied the movements of a star known as S2, they found that both the black hole and dark matter models could explain its behavior equally well. This suggests we may not have enough data yet to definitively say what’s at the center.
Moreover, the Gaia spacecraft’s mapping of the Milky Way has provided further insight. It shows that the galaxy’s rotation slows as you move further from the center. This slowdown, known as a “Keplerian decline,” might be better explained by a vast dark matter halo surrounding the Milky Way.
As Argüelles notes, this study is the first time a model of dark matter has connected various scale observations in the galaxy, from the movement of the S stars to the overall galactic rotation.
Looking ahead, future observations may soon settle this debate. Scientists hope to gather more precise data on stellar orbits, especially for stars closer to Sgr A*. Additionally, new images from the Event Horizon Telescope may highlight features that separate a black hole from a potential dark matter core.
This ongoing inquiry could reshape our understanding of the universe. As we gather more information about Sgr A*, we may finally uncover the true nature of what lies at the heart of our galaxy.
For further insights, check the full research in the Monthly Notices of the Royal Astronomical Society here.
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