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. It’s so quiet, astronomers refer to it as “dead”, which means it should be relatively easy to detect dark matter-produced gamma rays.
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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. It seems like every other day astronomers find something new and incredible about it that can either simply amaze us or contradict everything we knew about it. Astronomer Evan Kirby and his team found out, while they were tracking the Triangulum II galaxy with the Keck Observatory, that this particular galaxy has a massive density of dark matter. “The galaxy is challenging to look at”, he says.
Scientists are still trying to hone in on little dark matter interacts with the remainder of the Universe.
“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”, he said. 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.
Triangulum II is a small, dim galaxy at the edge of the Milky way, about 117,000 light-years away from Earth.
They have theorised that the galaxy might contain the highest known concentration of dark matter – an mysterious substance believed to make up the majority of the universe. “After I had made my measurements, I was only thinking-wow”, Kirby said.
Dark matter is invisible to astronomers, who have to rely on how it interacts with other objects in order to know it is there.
Dark matter is elusive.
As always, research workers in this study are detecting dark matter based on its effects – as well as the absence of anything more likely to cause those effects. While current theories suggest that dark matter is constantly emitting gamma rays nearly everywhere in the universe, isolating these signals from other galactic noises – such as gamma rays emitted from pulsars – is an insurmountable challenge.
But, it hasn’t been definitively confirmed, though, that what Kirby measured is actually the total mass of the Triangulum II.
Scientists said this was the opposite of what was expected, and that this implied that Triangulum II is being pulled apart by the gravitational forces of the Milky Way galaxy.
Kirby will take measurements of these outer stars to see if the other group’s findings are correct. “That would make it the most excellent candidate for detecting dark matter with gamma rays”, says Kirby.
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Kirkby and his colleagues published their findings in The Astrophysical Journal Letters on Nov.17. Judith Cohen (PhD ’71), the Kate Van Nuys Page Professor of Astronomy, is a Caltech coauthor.
