Could there be any alternative to a supermassive black hole that might explain Sgr A*?

Question

I am aware of How do we know the stars orbiting Sgr A* are orbiting a supermassive black hole and not just the center of mass of the Milky Way galaxy?, which asks why the motions of stars near the Galactic centre suggest a 4 million solar mass black hole.

But are there any theoretical ideas to explain these observations, that avoid the conclusion of a black hole, that remain unfalsified?

And will subsequent observations (e.g. with the Event Horizon telescope) be able to falsify these alternatives or indeed the hypothesis of a supermassive black hole?

Answer 1

Most mundane alternative explanations (like a very dense star cluster) have been ruled out by measuring the trajectories of nearby stars. These make clear that we are dealing with a compact object of roughly 4 million solar masses.

A black hole seems the least exotic of the objects that it could, as it requires no new physics. However, various exotic explanation such a boson star or a gravastar can be offered. However, these typically require the introduction of new physics, and even then no clear mechanisms for their formation might be available.

The Event Horizon telescope certainly will be able to further constrain hypothetically exotic alternatives. (Although it may still not rule all of them out completely.)

Answer 2

If the black hole wasn’t there you bet there would absolutely be theories trying to explain this. But there is like many other galaxies a supermassive Black Hole near the center of the entire galaxy. With the understanding of incredible gravitational pull from supermassive BH’s, it’s evident from perspective and what scientific evidence we can gather that the BH is the reason. And keeping in mind many galaxies have these in the “center” and the galaxies with the more spin or flow in design consist of these SUPERMASSIVE Black Holes in the center. While galaxies with out a supermassive BH centered are not so spiral so to speak but more chaotic and without what we perceive as a smooth productive flow. Hinting that the BH is the reason.