A team of University of Cambridge scientists has discovered a new dwarf galaxy - the Crater 2 - orbiting the Milky Way that spans farther than almost every other known Milky Way satellite. Researchers believe that the new galaxy, which appeared in Earth's telescopes seemingly out of nowhere, could belong to a small group of galaxies that is making its way into ours.
Current simulations suggest the Milky Way gained its large size through the mergers of smaller galaxies. Furthermore, they suggest that it is possible for whole groups of galaxies to fall into a single giant galaxy simultaneously, with one example being the Large and Small Magellanic Clouds, two galaxies that likely orbit each other.
The newly discovered galaxy is located around 380,000 light years away from our own in the constellation Crater.
"It's the fourth largest satellite of the Milky Way," said Gabriel Torrealba, a researcher from the University of Cambridge and first author of the study.
In addition to the Crater 2, the largest galaxies that orbit our own include the Sagittarius dwarf and the aforementioned Magellanic Clouds.
The team determined the size of the galaxy by obtaining its "half-light diameter," which encloses the brightest section of the galaxy and emits half of its light. The Crater 2 possesses a half-life diameter of approximately 7,000 light years, almost twice as big as the full moon.
Although not visible to the human eye, individual stars within Crater 2 are. Torrealba and his team uncovered its existence by using computers to examine over-densities of stars in data from a Chile telescope.
Why did the galaxy remain unseen for so long? Due to the distance between its stars, it possesses a ghostly appearance that made it difficult for scientists to detect until now.
Torrealba believes that there might be other galaxies near the Crater 2, including three dwarf galaxies in Leo, that are falling towards our own along with it.
Due to its round shape, the team believes that for the majority of its life, the dwarf galaxy never made its way close to a giant galaxy. If it had, it would have been bent out of shape by the larger galaxy's gravity.
The findings were published in the April 13 issue of the Monthly Notices of the Royal Astronomical Society.
