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‘Dead’ Galaxy May Harbor Highest Known Dark Matter Concentration

Milky Way Galaxy

Triangulum II is a relatively small galaxy located at the edge of the Milky Way that is considered “dead” because it no longer harbors the necessary ingredients to form new stars, but according to Evan Kirby, an assistant professor of astronomy at CalTech, what it lacks might me overshadowed by what could be the highest concentration of dark matter ever detected in a galaxy.

When Kirby measured the mass of the nearby galaxy, which is composed of roughly 1,000 stars, he found it “challenging to look at” because there were only six stars bright enough to examine with the Keck telescope. In order to measure the mass, he measured the velocity of the stars in order to determine the mass of the galaxy’s mass through the inference of the gravitational force exerted on the stars.

While his finding hasn’t been definitively confirmed, he stated in a CalTech news release that his possible discovery implies the existence of “a ton of densely packed dark matter” — the ratio of which to luminous matter being the highest of any known galaxy.

Following his measurements, the CalTech astronomer says he was just thinking “wow.”

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 (…) 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.

If Kirby’s measurements are proven correct, it could mean that the neighboring galaxy is literally being ripped apart by the Milky Way’s gravity, as measurements conducted by a group of researchers from the University of Strasbourg in France previously found the stars just outside of the galaxy to be doing the opposite of what is to be expected — moving closing towards the galaxy’s center.

According to Kirby, his next step is to verify the University of Strasbourg’s findings and if it turns out that the outer stars “aren’t actually moving faster than the inner ones, then the galaxy could be in what’s called dynamic equilibrium.” As far as gamma ray based dark matter detection goes, this would, according to Kirby, “make it the most excellent candidate” available at this time.

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