ESA's Gaia finds new galaxy 'Pontus' that crashed into Milky Way 8-10 billion years ago

About 12 billion years after being formed, the Milky Way galaxy continues to expand, in both mass and size, by engulfing many smaller galaxies. Recent data from the European Space Agency's (ESA) Gaia spacecraft has found evidence of a new member that fell into the Milky Way around eight to ten billion years ago. ESA revealed that the evidence was gathered using data based on Gaia’s early third data release (EDR3), which is targeted for release on June 13, 2022. The agency says that the account would provide even more detailed information about the Milky Way’s past, present, and future.

Galaxy named 'Pontus'

The galaxy, which is said to be the newest member in the Milky Way is named Pontus, which means 'the sea' and is the name of one of the first children of Gaia, the Greek goddess of the Earth. Led by Khyati Malhan, a Humboldt Fellow at the Max-Planck-Institut für Astronomie in Germany, the team discovered that Pontus has been pulled apart by the Milky Way.

(Yellow squares represent globular clusters, triangles represent satellite galaxies, and small dots are stellar streams. Image: ESA)

The astronomers identified the new member among six distinct groups, where each of them represented a merger taking place with the Milky Way. These groups were created after studying 170 globular clusters, 41 stellar streams and 46 satellites galaxies of the Milky Way. After the team plotted the objects according to their energy and momentum, the experts found that 25% of these objects fall into the said groups. Since five had already been identified during surveys, one stood out which was named Pontus.

However, it is worth noting that while Pontus is the newest member, it is the other merger event 'Sagittarius' which is the most recent. Since it has not been completely disrupted by the Milky Way, the astronomers concluded that it might have fallen into our galaxy no earlier than five to six billion years ago. ESA says that revealing the ‘family tree’ of smaller galaxies, that have helped make the Milky Way what it is today, allows reconstructing the history of our galaxy. "Piece by piece, astronomers are fitting together the merger history of the Galaxy, and Gaia data is proving invaluable", the agency said in a statement. 

Image: NASA