Scientists have just found that a peculiar galaxy in our galaxy's neighborhood is composed of 99.99 percent dark matter, the latest issue of the Astrophysical Journal Letters reported.
The discovery of Dragonfly 44, a seemingly ordinary and dim galaxy with almost the same size of the Milky Way, will possibly change everything in astronomy, according to a paper published in the Astrophysical Journal Letters.
The galaxy is relatively nearby -- only 300 million light-years -- but it only came to astronomers' attention lately because it has very few stars and is very dim.
It is made almost entirely of dark matter. No one really knows what dark matter is made of, but the scientists believe it exists because they can see the effects of gravity on other things in space.
The prevailing standard model of cosmology indicates that total mass-energy of the universal contains 4.9 percent ordinary matter, 26.8 percent dark matter and 68.3 percent dark energy.
The galaxy was first detected in 2015 through the Dragonfly Telephoto Array, a telescope invented and built by Pieter van Dokkum of Yale University and Robert Abraham of the University of Toronto.
Afterward, the scientists used some of the world's most powerful telescopes to monitor it further.
"Very soon after its discovery, we realized this galaxy held more than meets the eye. It has so few stars that it would quickly ripped apart unless something was holding it together," said van Dukkom, who is also the lead author of a paper in the Astrophysical Journal Letters.
Van Dukkom believed the galaxy is likely made of dark matter because the velocities of stars within it are much higher than what his team had expected, indicating that it has mass greater than what can be detected through telescopes.
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.
Van Dokkum said the discovery of Dragonfly 44 challenges existing notions on the formation of galaxies.
"It means we don't understand, kind of fundamentally, how galaxy formation works," says von Dokkum.
