Anomalies in Time Delays of Lensed Gravitational Waves and Dark Matter Substructures

Understand

The cold dark matter scenario of hierarchical large-scale structure formation predicts the existence of abundant subhalos around large galaxies.

• However, the number of observed dwarf galaxies is far from this theoretical prediction, suggesting that most of the subhalos could be dark or quite faint.
• Gravitational lensing is a powerful tool to probe the mass distribution directly irrespective of whether it is visible or dark.
• Time delay anomalies in strongly lensed quasar systems are complementary to flux ratio anomalies in probing dark matter substructure in galaxies.