An oddball galaxy thought to be almost devoid of dark matter seems to have a surprisingly normal population of stars — hinting at a dramatic past.
Dark matter is the enigmatic ‘stuff’ that is thought to make up most of the matter in the Universe, but cannot be detected directly. Researchers think that galaxies are surrounded by dark-matter haloes much greater in mass than the galaxies’ stars. But the faint galaxy NGC 1052-DF2 is an outlier that seems to have little or no dark matter.
A team led by Jérémy Fensch at the European Southern Observatory in Garching, Germany, performed a chemical analysis of DF2’s stars. This revealed that their fraction of relatively heavy elements is similar to that of other galaxies with a similar total mass of stars. This is surprising, because DF2’s lack of dark matter — which exerts a gravitational pull — should make it easier for heavier elements to escape the galaxy.
The finding supports the theory that DF2’s gas, from which its stars formed, originated in a much larger host galaxy with a typical dark matter halo, and was expelled in a collision with another galaxy.