An extended halo around an ancient dwarf galaxy

Understand

The Milky Way is surrounded by dozens of ultra-faint (< $10^5$ solar luminosities) dwarf satellite galaxies.

• They are the surviving remnants of the earliest galaxies, as confirmed by their ancient (~13 billion years old) and chemically primitive stars.
• Simulations suggest that these systems formed within extended dark matter halos and experienced early galaxy mergers and supernova feedback.
• However, the signatures of these events would lie outside their core regions (>2 half-light radii), which are spectroscopically unstudied due to the sparseness of their distant stars.