The Milky Way's thick disk takes shape
Our galaxy settles into a flattened, rotating body of stars about 11 billion years ago.
- When
- Known to
- ± 500 million years
- Era
- Galaxy Assembly, Stelliferous
The thick disk forms out of the Milky Way's earliest star-forming population, and is later puffed up and heated by the mergers that follow. Its stars are old, metal-poor and orbit on wider, more tilted paths than the Sun's. Reconstructing its age from asteroseismology and Gaia data has repeatedly pushed its formation earlier than expected.