Small galaxy may hold secret of dark matter

Caltech Astronomy Assistant Professor Evan Kirkby measured the mass of Triangulum II, a small and faint galaxy that is made up of only about 1,000 stars, by examining the velocity of six stars found in the galaxy’s center. Researchers claim that this galaxy has the highest ratio of dark matter to luminous matter of all. In fact, the theory goes that dark matter might be in fact the main source of mass in this galaxy, which explains why there are few stars to begin with.

It is made up of around 1,000 stars, the Milky Way by comparison boasts at least 100 billion, and is considered to be a “dead” galaxy because it is no longer producing new stars. He tells the Institute’s publication that Triangulum II is “hard to look at” because it only has six luminous stars that are visible from Earth using the Keck telescope. Even more, they realized that the tiny galaxy possibly possesses the highest concentration of dark matter yet discovered in any galaxy. It is widely believed that there is not a lot of dark matter interfering with the mechanisms of the Universe, but there is enough out there to drive scientists mad with curiosity. But Triangulum II could have a dark secret – one that makes it the most fascinating ghost town in space.

For those who are not familiar with dark matter, it is the opposite of matter, of course, but it does not abide the same rules as matter does in terms of interacting with light.

In a paper published in the Astrophysical Journal Letters, researchers suggest that the mysterious, unseen matter may be responsible for Triangulum II’s abysmally low star count. This Caltech simulation shows the predicted distribution of stars (left) and dark matter (right) around a galaxy on the edge of the Milky Way. But because Triangulum is in our cosmic backyard, astronomers may get a chance to peak into the dark matter galaxy by looking for evidence of gamma radiation, a byproduct of dark matter particles crashing into each other. This collision will produce gamma rays that scientists on Earth can detect. Triangulum II is not capable of forming stars, since it lacks gas and other types of star formation materials, causing astronomers to often refer to it as “dead”.

Another group, led by researchers from the University of Strasbourg in France, measured the velocities of stars just outside the Triangulum II and found that these stars are actually moving faster than the stars near the galaxy’s center – and this is the opposite of what scientists expected. This could suggest that the little galaxy is being pulled apart, or “tidally disrupted”, by the Milky Way’s gravity. “That would make it the most excellent candidate for detecting dark matter with gamma rays”, says Kirby.

Kirby said is next step will be verify those findings.

Kirby is planning to measure those findings and says “If it turns out that those outer stars aren’t actually moving faster than the inner one’s, then the galaxy could be in what’s called dynamic equilibrium”.