Very compact objects probe extreme gravitational fields and may be the key to understand
outstanding puzzles in fundamental physics. These include the nature of dark matter, the …

One century after its formulation, Einstein's general relativity (GR) has made remarkable
predictions and turned out to be compatible with all experimental tests. Most of these tests …

It is commonly believed that the ringdown signal from a binary coalescence provides a
conclusive proof for the formation of an event horizon after the merger. This expectation is …

Quasinormal modes are eigenmodes of dissipative systems. Perturbations of classical
gravitational backgrounds involving black holes or branes naturally lead to quasinormal …

This review is focused on tests of Einstein's theory of general relativity with gravitational
waves that are detectable by ground-based interferometers and pulsar-timing experiments …

Ultracompact objects are self-gravitating systems with a light ring. It was recently suggested
that fluctuations in the background of these objects are extremely long lived and might turn …

Deep conceptual problems associated with classical black holes can be addressed in string
theory by the “fuzzball” paradigm, which provides a microscopic description of a black hole …

Extreme mass-ratio inspirals (EMRIs) detectable by the Laser Interferometer Space Antenna
are unique probes of the nature of supermassive compact objects. We compute the …

A new final endpoint of complete gravitational collapse is proposed. By extending the
concept of Bose–Einstein condensation to gravitational systems, a static, spherically …

A generic feature of nearly out-of-equilibrium dissipative systems is that they resonate
through a set of quasinormal modes. Black holes—the absorbing objects par excellence …