By measuring the mass of a nearby dwarf galaxy, astronomers have found the highest concentration of dark matter in any known galaxy.
Triangulum II is a small, faint galaxy at the edge of the Milky Way, made up of only about 1,000 stars.
Assistant professor of astronomy Evan Kirby measured the mass of Triangulum II by examining the velocity of six stars whipping around the galaxy’s centre.
“Only six of its stars were luminous enough to see with the Keck Observatory in Hawaii,” Kirby said.
By measuring these stars’ velocity, Kirby could infer the gravitational force exerted on the stars and thereby determine the mass of the galaxy.
Dark matter is called “dark” for a good reason. Their existence is inferred by their gravitational influence in galaxies, but no one has ever directly observed signals from dark matter till date.
“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,” Kirby explained.
“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,” he added.
Triangulum II can become a leading candidate for efforts to directly detect the signatures of dark matter.
While current theories predict that dark matter is producing gamma rays almost everywhere in the universe, detecting these particular signals among other galactic noises is a challenge.
Triangulum II, on the other hand, is a very quiet galaxy.
It lacks the gas and other material necessary to form stars, so it isn’t forming new stars and astronomers call it “dead”.
“Any gamma ray signals coming from colliding dark matter particles would theoretically be clearly visible,” the authors noted in the paper appeared in the Astrophysical Journal Letters.