On Thursday, Aug. 25, scientists announced the discovery of a galaxy with the same mass as the Milky Way but contains 99.99 percent dark matter, which is an elusive and undetected substance.
Known as Dragonfly 44, the newly identified galaxy was first detected through the Dragonfly Telephoto Array in Toronto. Afterward, scientists used the world's most powerful telescopes, the Gemini North telescope at the Gemini Observatory and the Keck II telescope at the W.M. Keck Observatory, to monitor it further.
Although the galaxy is not the first to be identified with presence of dark matter, its discovery is special because it is the only average-sized galaxy nearly dominated by dark matter.
Pieter van Dokkum, an astronomer from Yale University, says soon after the galaxy's discovery, they realized there was more to it than meets the eye.
Undetected Dark Matter
Dragonfly 44 is located about 300 million light-years away from our planet and is considered a dim galaxy with very few stars. According to van Dokkum, the dim galaxy has so few stars that it would be rapidly ripped apart unless it was being held together by something.
Scientists believe the galaxy is likely made up of dark matter because the velocities of stars within it are much higher than what they had expected, indicating that it has a mass greater than what can be detected through telescopes.
Furthermore, although Dragonfly 44 has the same mass as our own galaxy, it's actually the "Dark Twin" and is different from our galaxy by a factor of 100.
How The Discovery Changes Everything
The dim galaxy is such a novelty in the line of research that astrophysicists currently study. According to van Dokkum, the discovery of Dragonfly 44 challenges existing notions on the formation of galaxies.
He says that prior to the research, they thought the ratio of dark matter was something they already understood.
For instance, dark matter is thought to outnumber regular matter — ordinary matter composed by atoms — by 5 to 1 in the universe.
Additionally, scientists thought the formation of stars was related to how much dark matter is present. However, Dragonfly 44 turns this last idea around.
“It means we don’t understand, kind of fundamentally, how galaxy formation works," says van Dokkum.
Meanwhile, the race to detect other galaxies similar to Dragonfly 44 is on. Because dark matter is believed to emit a faint ultraviolet signal, experts hope a neighboring galaxy with dark matter can provide the first evidence of the elusive substance's existence.
Details of the report were published in the Astrophysical Journal Letters.
