A team of astronomers from the University of Cambridge recently identified nine new dwarf galaxies orbiting the Milky Way – the largest number to have ever been discovered at once. The findings were published Tuesday in the Astrophysical Journal.
The discovery is the first of its kind in roughly a decade and is based on newly released imaging data taken from the Dark Energy Survey. According to the Washington Post, the new galaxies are a billion times dimmer than the Milky Way, and a million times less massive. They are also located near the two biggest dwarf galaxies currently orbiting the Milky Way: the Large and Small Megallanic Cloud.
At the moment, the researchers are only certain that three of the nine objects are actually dwarf galaxies. The other six might be what astronomers call globular clusters, or groups of stars that are held together by the gravity of a galaxy, rather than dark matter.
But dark matter, which is thought to comprise over a quarter of the universe’s mass, is what scientists are most eager to study. Dark matter is the term used to describe the substance that takes up the space not held by stars, planets, and other objects scientists already have an understanding of.
At the moment, information about dark matter is very limited. Astronomers do not under its properties, and it also cannot be seen with telescope. Yet, we can observe the effects of its gravitational pull. The discovery of the dwarf galaxies is particularly interesting because of of their composition: they contain way more dark matter than larger galaxies.
“The discovery of so many satellites in such a small area of the sky was completely unexpected,” states Sergey Koposov of Cambridge’s Institute of Astronomy, the study’s lead author, in a statement. “I could not believe my eyes.”
Thus, the dwarf satellites are essential to allow astronomers to get a better understanding of dark matter. According to Vasily Belokurov of the Institute of Astronomy, one of the study’s co-authors, “We need to find them to determine whether our cosmological picture makes sense.”
The results of the findings are being released today, along with the results of a separate survey by astronomers with the Dark Energy Survey, which aims to understand the dynamics of the expansion and growth of the universe.