In studying Triangulum II, a dwarf galaxy nearby the Milky Way, researchers from CalTech have come to realize that it has the largest concentration of dark matter ever known. It wasn’t obvious at first, seeing as how dark matter is invisible to both eyes and instruments, but the realization came when they went to measure its mass, finding that it was much, much denser than it should’ve been for having so few stars.
The astronomers studied the velocity of six stars as they traveled around the galaxy’s center. “The total mass I measured was much, much greater than the mass of the total number of stars — implying that there’s a ton of densely packed dark matter contributing to the total mass,” said Evan Kirby. Dark matter is detected by studying its indirect effects, such as its gravitational influence.
Triangulum II is believed to only have 1,000 stars, which accounts for how little light is emitted from the galaxy. But when compared to its massive size, it implies that it’s mostly made up of dense clouds of dark matter — as much as five times more dark matter than ordinary matter. “The ratio of dark matter to luminous matter is the highest of any galaxy we know. After I had made my measurements, I was just thinking — wow,” added Kirby.
While the scientists have to determine Triangulum II’s overall mass, the hope is that the galaxy will become a prime source to better study the signatures of dark matter. The real benefit is that the galaxy is so close, which will allow astronomers to look for gamma radiation, which is produced when dark matter particles collide.