The galaxy, baptized as Dragonfly 44 (Dragonfly 44) is located in the constellation Coma and had been being investigated for a year due to its unusual composition: it is a diffuse mass similar in size to the Milky Way , but with many fewer stars. “As soon as we discovered it, we realized that this galaxy was special. It contains so few stars that it would be easily ejected from where it is if it weren’t for some force holding it down,” says Yale University astronomer Pieter van Dokkum, lead author of the study published in Astrophysical Journal Letters .
Van Dokkum’s team was able to get good images of Dragonfly 44 from the WM Keck Observatory and the Gemini North Telescope, both in Hawaii . For six nights, astronomers measured the speeds of the stars in the galaxy, which are indicators of galactic mass. The faster they move, the greater the mass of the galaxy. Surprisingly, they appreciated that they were moving much faster than expected and deduced that the reason was that Dragonfly 44 contains a large amount of invisible mass.
The mass of Dragonfly 44 has been estimated to be one trillion times the mass of the Sun , similar to that of the Milky Way. However, only 0.01% of it is made up of stars and “normal” matter. The remaining 99.99% is made up of dark matter, the invisible material that probably occupies more than 90% of the entire Universe. The researchers noted that it is not the first galaxy made up of dark matter to be found. For example, spheroidal dwarf galaxies have a similar composition, but are about 10,000 times less massive than Dragonfly 44.
At the moment they do not know how this galaxy could have been formed.
Caption: The Dragonfly Galaxy 44.
Credit: Pieter van Dokkum, Roberto Abraham, Gemini, Sloan Digital Sky SurveyClose.
