I think this is the paper behind the article.

They propose “dark stars” which formed when dark matter clouds collapsed, the mass then pulls in hydrogen and helium. The resulting star is huge but it is a relatively cool star.

They believe they have found 3 candidates which could be galaxies (containing population III stars) or super massive dark stars.

The test is if they absorb or emit helium a helium signature. If they absorb it, they are dark stars if they emit helium they are galaxies.

The nice thing is there are only 2 proposed types of dark matter which could make a dark star work so it would help us work out what dark matter is.