California Institute of Technology | 2015 Nov 18
[img3="Dwarf galaxies have few stars but lots of dark matter. This Caltech FIRE (Feedback in Realistic Environments) simulation from shows the predicted distribution of stars (left) and dark matter (right) around a galaxy like the Milky Way. The red circle shows a dwarf galaxy like Triangulum II. Although it has a lot of dark matter, it has very few stars. Dark matter-dominated galaxies like Triangulum II are excellent prospects for detecting the gamma-ray signal from dark matter self-annihilation.Dark matter is called "dark" for a good reason. Although they outweigh particles of regular matter by more than a factor of 5, particles of dark matter are elusive. Their existence is inferred by their gravitational influence in galaxies, but no one has ever directly observed signals from dark matter. Now, by measuring the mass of a nearby dwarf galaxy called Triangulum II, Assistant Professor of Astronomy Evan Kirby may have found the highest concentration of dark matter in any known galaxy.
(Credit: A. Wetzel and P. Hopkins, Caltech)"]http://s3-us-west-1.amazonaws.com/www-p ... WS-WEB.jpg[/img3][hr][/hr]
Triangulum II is a small, faint galaxy at the edge of the Milky Way, made up of only about 1,000 stars. Kirby measured the mass of Triangulum II by examining the velocity of six stars whipping around the galaxy's center. "The galaxy is challenging to look at," he says. "Only six of its stars were luminous enough to see with the Keck telescope." By measuring these stars' velocity, Kirby could infer the gravitational force exerted on the stars and thereby determine the mass of the galaxy.
"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 says. "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."
Triangulum II could thus become a leading candidate for efforts to directly detect the signatures of dark matter. Certain particles of dark matter, called supersymmetric WIMPs (weakly interacting massive particles), will annihilate one another upon colliding and produce gamma rays that can then be detected from Earth. ...
Triangulum II: Possibly a Very Dense Ultra-Faint Dwarf Galaxy - Evan N. Kirby et al
- Astrophysical Journal Letters 814(1):L7 (2015 Nov 20) DOI: 10.1088/2041-8205/814/1/L7
arXiv.org > astro-ph > arXiv:1510.03856 > 13 Oct 2015 (v1), 12 Nov 2015 (v3)
