Pure disc galaxy

This article or the following section is not adequately provided with supporting documents ( e.g. individual evidence ). Information without sufficient evidence could be removed soon. Please help Wikipedia by researching the information and including good evidence.

A pure-disc galaxy is a spiral galaxy that has no central bulge . An example is NGC 3621 in the constellation Water Snake .

It is currently believed that bulges form when galaxies collide and merge. Simulations at the Shanghai Astronomical Observatory suggest, however, that bulges could form without merging.

• 

  Image of the spiral galaxy NGC 3621 with the Wide Field Imager (WFI) of the La Silla Observatory

• 

  Photo of the spiral galaxy Messier 101 from the Hubble Space Telescope .

Individual evidence

1. ↑ Juntai Shen et al .: Our Milky Way as a Pure-Disk Galaxy - A Challenge for Galaxy Formation . arxiv : 1005.0385v2