Discovery of a Galaxy With Little Detectable Dark Matter
Using the W. M. Keck Observatory on Maunakea, astronomers measured the stellar velocities of a faint galaxy to assess its dark matter content. The spectroscopy revealed that the stars move slower than they would if a massive dark matter halo were present.
The galaxy’s mass-to-light ratio is unusually low, indicating a minimal dark matter fraction. This makes it the third known system of its kind, following two earlier reports of similar objects.
The object lies within a striking linear arrangement of several celestial bodies resembling a cosmic stream. Such features can arise when two galaxies pass close enough for their gravitational fields to tug stars and gas away.
If the linear feature stems from an ancient collision, it could account for the apparent dark matter deficit: a violent encounter might have stripped or redistributed the dark matter halo while leaving the stellar component relatively intact.