Dark Matter Found |in Neighboring Galaxy

     (CN) – A California Institute of Technology astronomy professor says he may have found the most concentrated mass of dark matter in any known galaxy.
     Evan Kirby, assistant professor of astronomy at Caltech, was measuring the velocity of six out of the 1,000 stars making up Triangulum II, a dwarf galaxy bordering the Milky Way, when he made the discovery, Lori Dajose wrote in a university report.
     “The galaxy is challenging to look at,” Kirby explained later. “Only six of its stars were luminous enough to see with the Keck telescope.”
     The Keck telescopes, located at the W.M. Keck observatory on Mauna Kea in Hawaii, are the world’s largest optical and infrared telescopes.
     Those measurements allowed Kirby to infer the gravitational force exerted on the stars and, in turn, the mass of the galaxy, Dajose wrote.
     “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.”
     The existence of dark matter particles – which outweigh particles of regular matter by more than a factor of 5 – is inferred by their gravitational influence in galaxies, the report says.
     Though no one has ever directly observed signals from dark matter, Triangulum II might get us a step closer, Dajose reported.
     Dark matter can also be detected from gamma rays produced by colliding supersymmetric WIMPs, or ‘weakly interacting massive particles’ of dark matter, almost everywhere in the universe, the report says.
     But those rays are hard to detect among other galactic noises, like gamma rays emitted from pulsars, or fast-spinning neutron stars, Dajose wrote.
     Indeed, astronomers call Triangulum II “dead,” since it lacks the gas and other material necessary to form stars, so theoretically, gamma ray signals coming from colliding dark matter particles would be clearly visible, the report states.
     Yet it is not totally certain that Kirby measured the total mass of the galaxy, Dajose said.
     A group led by researchers from the University of Strasbourg in France reportedly found that stars just outside Triangulum II are moving faster than the stars closer to the galaxy’s center.
     That not only contradicts what is expected, but could mean that Triangulum II is being pulled apart, or “tidally disrupted,” by the Milky Way’s gravity, the report states.
     Kirby said he plans to make measurements to confirm the other group’s findings.
     “If it turns out that those outer stars aren’t actually moving faster than the inner ones, then the galaxy could be in what’s called dynamic equilibrium,” Kirby said. “That would make it the most excellent candidate for detecting dark matter with gamma rays.”

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