While measuring the speed of stars whirling around a nearby dwarf galaxy, astronomers have realized that a reservoir of dark matter may be lurking within.
Astronomers grew suspicious of Triangulum II when they tried to measure its mass. Using 6 stars as tracers, they measured their speed around the galaxy’s center. Known only to contain around a 1,000 stars, this particular galaxy is a welterweight by cosmic standards, but looks can be deceiving. What they found was an amazingly dense galaxy apparently filled with dark matter.
“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 astronomer Evan Kirby, of the California Institute of Technology (Caltech) in Pasadena. “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.”
Indeed, dark matter is believed to account for the vast majority of matter in the entire universe — approximately 85 percent is thought to be composed of dark matter particles that do not interact with normal matter, except via the gravitational force.