Computer modelling then showed the dwarf galaxy first crashed into the Milky Way some 2.7 billion years ago.
However, the researchers originally assumed the dwarf galaxy had been pulled towards the Milky Way through a so-called “tidal merger”.
The process is a fairly common one but this was not the case with the Virgo Merger.
And the astronomers were not looking for evidence in support of a violent collision.
Thomas Donlon II, a Rensselaer graduate student and first author on the paper, said: “There are other galaxies, typically more spherical galaxies, that have a very pronounced shell structure, so you know that these things happen, but we’ve looked in the Milky Way and hadn’t seen really obvious, gigantic shells.”