Using the help of the European Space Agency’s Gaia satellite, astronomers have made a remarkable discovery: They have detected a faint Ghost Galaxy hiding behind the Milky Way’s disc.
The Ghost Galaxy, dubbed Antila 2 or Ant 2, is around 10,000 times dimmer than other known satellite galaxies of the Milky Way and is considered a dwarf galaxy.
The discovery was made after a group of international scientists teamed up and combed through old Gaia data.
Speaking about the discovery, lead author of the study Gabriel Torrealba said: “This is a ghost of a galaxy.”
“Objects as diffuse as Ant 2 have simply not been seen before. Our discovery was only possible thanks to the quality of the Gaia data.”
According to astronomical data, it is believed that dwarf galaxies were among the first structure to come into existence in the early universe.
And despite its size, astronomers say that the object is giving off much less light than what experts had anticipated.
Astronomers also used data on PR Lyrae stars in order to pinpoint the extremely well-hidden galaxy in the Milky Way’s neighborhood.
“RR Lyrae had been found in every known dwarf satellite, so when we found a group of them sitting above the Galactic disc, we weren’t totally surprised,” explained -co-author Vasily Belokurov, from Cambridge’s Institute of Astronomy.
“But when we looked closer at their location on the sky it turned out we found something new, as no previously identified object came up in any of the databases we searched through.”
It was an incredible and exciting discovery.
And after spotting the set of stars, astronomers knew that they had limited time to gather more information about the object as Earths motion would soon make An2 unobservable for months.
But despite not having much time to make further observations, astronomers successfully managed the spectra of more than 100 red giant stars in time, which eventually allowed them to confirm the discovery.
Astronomers explain that Ant2 is located some 130,000 light-years from the Milky Way, and has a much smaller mass than expected given its size.
“The simplest explanation of why Ant 2 appears to have so little mass today is that it is being taken apart by the Galactic tides of the Milky Way,” explained co-author Sergey Koposov, from Carnegie Mellon University.
“What remains unexplained, however, is the object’s giant size. Normally, as galaxies lose mass to the Milky Way’s tides, they shrink, not grow,” added Koposov.
“Compared to the rest of the 60 or so Milky Way satellites, Ant 2 is an oddball,” said co-author Matthew Walker.
“We are wondering whether this galaxy is just the tip of an iceberg, and the Milky Way is surrounded by a large population of nearly invisible dwarfs similar to this one,” concluded Walker.