Anomalous Galaxy Thought To Be 99.99% Dark Matter Is Actually Normal

The mystery of a galaxy that was believed to be 99.99% dark matter has finally been solved. As it turns out, it's not as anomalous as previously thought.

Dark matter is perhaps one of the bigger mysteries in the universe, with more known about what it's not that what it is. It is, however, useful in understanding the formation of galaxies, which typically have 10 to 300 times dark matter than visible matter. Our own Milky Way, for instance, has about 10 times as much dark matter as all the stars and gas combined, NASA notes.

But in 2016, it was discovered that a galaxy called Dragonfly 44 has 10,000 times more dark matter than stars. This meant that Dragonfly 44 is essentially made up of 99.99% dark matter, making the galaxy an anomaly.

In a new study published in the Monthly Notices of the Royal Astronomical Society, an international team of researchers studied Dragonfly 44 and found that it may actually be more normal than initially believed. This is because compared to the initial study's report that there are 80 globular clusters around Dragonfly 44, the researchers found only 20.

As the news release from the Instituto de Astrofísica de Canarias (IAC) explains, globular clusters help determine the total mass of a galaxy. This, in turn, can help quantify the amount of dark matter since visible matter is typically just a "small fraction" of the total mass. In the case of Dragonfly 44, having the number go down from 80 to just 20 suggests a much lower quantity of dark matter.

According to the researchers, this means that the dark matter in Dragonfly 44 is just about 300 times that of visible matter, which is within the normal range. As the researchers put it, Dragonfly 44 is "not extraordinary in this respect."

"Dragonfly 44 has been an anomaly all these years that could not be explained with the existing galaxy formation models," study first author Teymoor Saifollahi said in the IAC news release. "Now we know that the previous results were wrong and that DF44 is not extraordinary. It is time to move on."