Butterfly in a Cocoon, Understanding the origin and morphology of Globular Cluster Streams: The case of GD-1

Understand

Tidally disrupted globular cluster streams are usually observed, and therefore perceived, as narrow, linear and one-dimensional structures in the 6D phase-space.

• Here we show that the GD-1 stellar stream ($\approx$ 30 pc wide), which is the tidal debris of a disrupted globular cluster, possesses a secondary diffuse and extended stellar component ($\approx$ 100 pc wide) around it, detected at >5$\sigma$ confidence level.
• Similar morphological properties are seen in synthetic streams that are produced from star clusters that are formed within dark matter sub-halos and then accrete onto a massive host galaxy.
• This lends credence to the idea that the progenitor of the highly retrograde GD-1 stream was originally formed outside of the Milky Way in a now defunct dark satellite galaxy.