Up until now, scientists have not been able to find any evidence of dark matter, which they say makes up 27% of our universe. The existence of this unobserved matter could only be detected by looking at its gravitational effects on galaxies. Now, a scientist looks at the edge of the Milky Way to find evidence.
Evan Kirby of the California Institute of Technology (CALTECH) measured the mass of Triangulum II, a dwarf galaxy lurking at the edge of Milky Way. His observation shows the galaxy is only composed of 1,000 stars and does not generate stars anymore, making it a "dead" galaxy.
To look for the evidence of dark matter, Kirby will observe the galaxy's six stars that release luminous matter.
"The ratio of dark matter to luminous matter is the highest of any galaxy we know," he said.
Furthermore, the total mass of the dwarf galaxy is extremely massive, compare to the size of Milky Way, even though Triangulum II is considered dead. So it implies the galaxy holds a ton of dark matter which significantly contributes to its total size.
Scientists first observed the Triangulum II earlier this year, and it exhibits extreme luminosity similar to the faintest galaxy in the universe-- Segue 1. But the Triangulum II is the best candidate to detect the signatures of dark matter. Kirby and his co-researchers explained that dark matter particles-- called supersymmetric weakly interacting massive particles or WIMPs-- destroy each as they interact with another. This interaction creates gamma rays that scientist here on Earth will try to observe.
In a dead galaxy like Triangulum II any signals of gamma rays from dark matter particles would theoretically be visible, experts said.
To support Kirby's research, a group of researchers from the University of Strasbourg in France studied the speed of stars around Triangulum II. They found that these stars moved faster than the stars in the center of the small galaxy.
This observation does not comply with the existing models of the galaxy, and it implies that Triangulum II is being pulled apart.
As of now, we only know that dark matter is responsible for the structures in the universe. It is the first of matter to settle down when the universe expanded and the first to form structures under its own gravitational pull.
Kirby's findings are published in The Astrophysical Journal Letters.