A doctoral thesis examines how compact objects behave in two quantum gravity frameworks —quadratic gravity and asymptotic safety— and what observational imprints they might leave. By analysing linear perturbations of the metrics, the work studies quasinormal modes, black hole shadows and Hawking radiation, aiming to bridge theoretical quantum gravity models with potentially measurable astrophysical phenomena.

The first part focuses on Einstein-Weyl gravity, where an additional massive spin-2 degree of freedom modifies the dynamics of compact objects. The analysis of tensor perturbations in static, spherically symmetric solutions reveals Gregory-Laflamme-type instabilities in the monopole sector, along with universal massive-field tails and the breakdown of the standard eikonal correspondence between quasinormal modes and null geodesics. The study pays particular attention to veiled singularities: horizonless configurations that satisfy a form of weak cosmic censorship and can mimic black hole shadows.

The second part addresses regular black holes in asymptotically safe gravity. Using the proper-time flow approach, the author constructs a dynamical regular black hole solution arising from gravitational collapse and analyses its perturbative stability and quasinormal mode spectrum, which shows characteristic deviations from the Schwarzschild black hole. While the predicted shadow remains compatible with current observational constraints, the modified evaporation process features lower temperatures and suppressed emission rates.

Such quantum corrections have direct consequences for primordial black holes and their possible contribution to dark matter: slower evaporation allows more low-mass objects to survive over the lifetime of the universe. The work concludes that the perturbative dynamics of compact objects offer a practical route to connect quantum gravity models with observable astrophysical phenomena.