No massive black holes in the Milky Way halo

Understand

The gravitational wave detectors have unveiled a population of massive black holes that do not resemble those observed in the Milky Way and whose origin is debated.

• According to one possible explanation, these black holes may have formed from density fluctuations in the early Universe (primordial black holes), and they should comprise from several to 100% of dark matter to explain the observed black hole merger rates.
• If such black holes existed in the Milky Way dark matter halo, they would cause long-timescale gravitational microlensing events lasting years.
• The previous experiments were not sufficiently sensitive to such events.