A small, nearby galaxy called Triangulum II appears to be mostly made up of dark matter. This type of galaxy has been sought after by astronomers for quite some time, as it could greatly aid in our quest to understand the physics of our universe and the nature of dark matter.
Indeed, a dark matter galaxy is a sort of holy grail to astronomers, mainly because none have been found yet. They are highly sought after, since discovering even one would enable astronomers to finally study dark matter, which has never been seen or observed directly, though its existence have long been predicted by detecting the effects that it has on our universe
Astronomers from Caltech came to their conclusion after measuring the velocities of six of the galaxy's stars and inferring the mass of Triangulum II. When the total mass greatly exceeded what they expected to find after taking the visible stars into account, the astronomers determined that their results could only be explained if Triangulum II contained a huge amount of densely-packed dark matter.
Dark matter is of great interest to astronomers because they estimate that it comprises about 23% of our universe. Regular matter - which our planet, the stars, and everything we see around us is made of - only makes up 4%. The rest (a staggering 73%) is dark energy. To this end, the study of dark matter would contribute significantly to our understanding of the universe.
Not all astronomers agree with the results of Caltech, however. Researchers from the University of Strasbourg in France found that according to their calculations, the stars just outside Triangulum II are moving faster than the stars closer to the galaxy's center, which is the opposite of what should be expected.
Despite this, the astronomers at Caltech still believe that their results are not in conflict with the other group's findings, and that the presence of dark matter in Triangulum II can actually explain the discrepancies that were found. In the end, further research is needed to determine which of the two teams is correct.