Recently, astronomers hit upon a galaxy as big as ours, and with an equivalent proportion of dark matter. It is called Dragonfly 44 and is situated about 300 million light years in the Coma constellation, with a mass hypothesised to be 1 trillion times that of the sun.
Astronomers from U.S. and Canada used the W.M. Keck Observatory and Gemini North telescope, located in Hawaii, to arrive at their conclusions. They wrote a paper titled "A High Stellar Velocity Dispersion and 100 Globular Clusters for the Ultra Diffuse Galaxy Dragonfly 44" that was published in the journal Astrophysical Journal Letters on Thursday.
Pieter van Dokkum, an astronomer at Yale University and lead author of the paper, said: "Very soon after its discovery, we realized this galaxy had to be more than meets the eye. It has so few stars that it would quickly be ripped apart unless something was holding it together."
The velocities of stars in Dragonfly 44 were assessed, with the help of data collected from Keck over six nights. "Star velocities are an indication of the galaxy's mass ... The faster the stars move, the more mass its galaxy will have," said the report.
The galaxy seemed to be less bright, yet the stars seemed to be speeding. Roberto Abraham of the University of Toronto, co-author of the paper, said: "It means that Dragonfly 44 has a huge amount of unseen mass."
Even though the new galaxy has the same number of stars as our own, just one-hundredth of one per cent is composed of familiar matter such as stars, dust and gas around the earth.
The Gemini North telescope exposed the Dragonfly 44's "halo of spherical clusters of stars around the galaxy's core, similar to the halo that surrounds our Milky Way galaxy."
How did such a galaxy get formed? Abraham has no clue. "The Gemini data show that a relatively large fraction of the stars is in the form of very compact clusters, and that is probably an important clue. But at the moment we're just guessing."
YouTube/NASA Goddard
