Do they have solid rings?

Astronomers at Vanderbilt claim to have identified 675 rogue stars they claim look as though they are inner galaxy stars (more metal because of recycling in the denser center) that were ejected by the black hole. They're red giants. If they came from the core they took about 10 million years to get here, which they suppose means they were yellow stars when they headed out, since apparently red giants don't last more than a few million years. The theory is that a binary system (of which there are plenty) falling into a black hole stands a chance of splitting the kick so that one falls in faster and the other is kicked away fast.

That's quite an addition (if accurate) to the 16 candidates astronomers already have. I can't get at the article yet. I'd like to know why they looked for red giants particularly. If the high "metalicity" ratio (of metals to H and He) they're looking for shows up best in red giants, there are probably a whale of a lot of other slingshot stars around. Of course it could be that they have their estimates for the tail of the distribution of metalicity wrong and these are ordinary stars. And (I wish I could find the report) the popular article didn't mention any velocity measurements. In fact, it said they were checking to see if these were "unusually red brown dwarfs instead of red giants. Because brown dwarfs produce a lot less light than red giants, they would have to be much closer to appear equally bright." Which could mess up velocity measurements...

UPDATE (3-May) to clarify what I mean by the tails of the distribution. The ratio of heavier elements to hydrogen/helium is going to vary star by star. Those that form in areas full of dust from vanished stars will pick up more. A few years scanning stars will give you a distribution of ratios. There'll be some average and a distribution about that average that typically looks a little like a bell curve (if you squint or only look at the part near the average). Far away from the average you typically get tails that don't look like a bell curve's: they drop off too fast or wayy too slow.

The point of their exercise is that these distributions aren't the same in the core of the galaxy; the average is higher. So if they underestimate the number of ordinary out-in-the-boondocks stars that have high "metalicity" they'll interpret them as "they don't belong there" type stars.

There are other possibilities as well. For example, if a red giant is in the process of absorbing a few planets, that could drive up the ratio. How much? That depends on how fast planets evaporate and how fast convection is in the outer layer of the star.

The team looked in a relatively clean area between us and Andromeda. Astronomers suspect that the Milky Way has indulged in collisions with other galaxies and clusters. These stars could be relics of some dispersed dust cloud from the center of a star cluster that collided and went away.