Besides requiring astronomers to dream up a new mnemonic for their stellar classification, the existence of a grey area between stars and planets reveals the extent to which the processes of planetary and stellarformation are still a mystery.
Astronomers have long theorized that there are many planets that have drifted away from their home stars, whether it's a too-loose gravitational pull during the planet's formation or a stellar tug-of-war.
That suggests a wave of star formation that travelled down the arms, set off by the collision with IC 4970, with the newest stellar neighbourhoods pushing the galaxy into the top spot in terms of size.