Space

Milky Way's central black hole could be a ball of dark matter

Milky Way's central black hole...
The center of the Milky Way is home to a massive compact object known as Sagittarius A* (bright spot to the right of center of the image)
The center of the Milky Way is home to a massive compact object known as Sagittarius A* (bright spot to the right of center of the image)
View 1 Image
The center of the Milky Way is home to a massive compact object known as Sagittarius A* (bright spot to the right of center of the image)
1/1
The center of the Milky Way is home to a massive compact object known as Sagittarius A* (bright spot to the right of center of the image)

Like most galaxies, the Milky Way is thought to host a supermassive black hole in its center – but perhaps its dark heart is made of different stuff. A new study proposes that it could instead be a dense core of dark matter, made up of hypothetical particles called “darkinos.”

The Milky Way is held together by a huge mass in the middle, equivalent to about 4 million Suns. Known as Sagittarius A* (Sgr A*), this massive object can’t be directly seen, but its existence can be inferred from the motions of stars around it. A supermassive black hole is the most logical candidate – but maybe it’s not the only explanation.

The doubts were seeded seven years ago. A gas cloud named G2 was found to be orbiting Sgr A*, due to pass perilously close to the object in early 2014. Astronomers watched with anticipation – if Sgr A* was a supermassive black hole as expected, then G2 should be torn to shreds before their eyes.

But surprisingly, G2 survived the sweep without issue. That’s led some scientists to speculate that perhaps it isn’t a gas cloud but a bloated dusty star, with enough gravity to keep its shape. In the new study however, the researchers questioned not the identity of G2, but Sgr A* itself.

Scientists at the International Center for Relativistic Astrophysics (ICRA) in Italy simulated what would happen if they replaced the supermassive black hole with a clump of dark matter. This mysterious stuff is already thought to be concentrated in the center of the galaxy, holding the whole thing together with its gravity.

The ICRA team found that if dark matter had certain properties, it could accurately account for a range of observations, in some cases better than the black hole model. This dark matter would consist of darkinos, neutral ultralight particles belonging to a group called fermions. These darkinos would clump together in the center of the galaxy, and spread into a more diffuse cloud further out.

A key characteristic of fermions is that only one of them can occupy a particular quantum state at a time in a given space, which limits how densely they can be packed together. As such, the core of this ball is a far less extreme environment than a supermassive black hole, which would allow G2 to pass by unscathed.

But that’s not the only observation that the model fits. The team found that if darkinos had a mass of around 56 keV, the simulation accurately predicted the motions of a cluster of nearby stars called the S-stars, as well as the rotation curve of the Milky Way’s outer halo.

As intriguing as the darkino hypothesis is, the case is far from settled. The supermassive black hole idea remains the most likely story, because it explains well-observed physics in a relatively simple way – and besides, we see black holes at the center of most other galaxies.

Still, it pays to keep an open mind, and the team says that further data releases could shed light on the idea, one way or the other.

The research was published in the journal Monthly Notices of the Royal Astronomical Society: Letters, with an earlier paper on the subject appearing in Astronomy & Astrophysics.

Source: INAF via Live Science

8 comments
8 comments
piperTom
Wow, this contradicts much of what we thought we knew about both dark matter and black holes. Dark matter was invented (yes, invented) to a problem with the orbital speed of stars; the speed does not fall off with distance from the core, as it should. (Babcock study in 1939 found unexpectedly rapid rotation in the outskirts of Andromeda.) Thus dark matter must be spread out, not concentrated. On the other issue, black holes form when the mass concentration prevents light from escaping without regard to what kind of mass it is.
bwana4swahili
The scientific method has five basic steps, plus one feedback step:
1. Make an observation.
2. Ask a question.
3. Form a hypothesis, or testable explanation.
4. Make a prediction based on the hypothesis.
5. Test the prediction.
6. Iterate: use the results to make new hypotheses or predictions.

I guess we've asked a question and into forming a hypothesis... But it is going to be a hard one to test!

Always lots of questions to keep scientists funded.
TechGazer
Here's a question: how does dark matter interact with black holes? Dark matter might normally spread out, but perhaps it collects on the event horizon, or inside (if 'inside' makes sense for a black hole).
wolf0579
This is just getting to be laughable. There is, in all seriousness, more evidence for the existence of Sasquatch and UFO's, than there is for the mythical "dark" matter.
neutrino23
This is very interesting as they can now start to fit data to a hypothesis. 56keV is really light, about a tenth the mass of an electron.

This is a direct contradiction to those suggesting that dark matter is its own anti-particle. In that hypothesis any two dark matter particles that met at the center of such a cloud would annihilate making the such a condensed matter cloud impossible. We'll see which ideas win out.
JPC-W
My first though was, "International Center for Relativistic Astrophysics (ICRA) in Italy," weren't these, (loosely speaking,) more or less the same group pf people, " who not so long ago were convinced that they had firm and clear experimental evidence of neutrinos traveling faster than light ?

Also I can't see how any such particle would fit into the Standard Model.

Sounds like a complete load of cobblers to me.
Worzel
It could also be a ball of Christmas pudding, or anything else one likes to imagine!
Karmudjun
This is interesting conjecture. If you study physics for more than a few semesters, you begin to understand the contradictions of the different models. It is hard to portray in 3 dimensional reality, but it is just as much of a stretch of explanations from the Norse understanding of the world with Thor riding through the clouds in a chariot striking lightning with Meljnor to Aristotle's view of mechanics of the known world (with astrophysics calculations resulting in the Antikythera Mechanism) to Galileo's version of the heavens & the mechanisms of the world (gravity - falling objects) to the development of quantum mechanics. Why the history lesson? Because each model - or theory - or concept - or as misstated - "invention" - MORE CLOSELY DESCRIBES THE FINDINGS OF CUTTING EDGE RESEARCH.

This research - these observations - attempt to explain why G2 and SGrA didn't behave according to established models - which were best explanations unifying most of the physics of the 1930's to the 2000's. There is no proof that this pondering of "what is happening and why it happened this way" is correct thinking, or even considers all the dynamics present. Hidden particles have been discovered time and again - I don't remember when X-Rays were things of fiction, that rocks could emit harmful health-impairing forces (Krypton - lookout Superman), but we not only understand these frequencies but we have harnessed it in fission and are able to harness fusion within a plasma cloud.

Physics derives laws from nature - then contemplates how these laws fail to explain - and if possible further study attempts to explain why variations occur. Then comes along a unified theory that better explains all the complex findings and behaviors and it all starts over again. It is called theoretical physics - even if it explains nuclear behavior down to quarks - because it is not an invention, but a concept to be tested. The only thing real - or solid enough to be invented - is the world around us that we observe and measure. Science is not open to misstatements and unfounded conjectures - that is for politics and economics, religion and early childhood educational practices.