Multimessenger Astrophysics and Cosmology

Compact stars, the dense remnants of massive stars formed after supernova explosions, pack roughly 1.4 solar masses into a radius of about 10 km, reaching densities beyond that of atomic nuclei. Their extreme compactness makes them unique laboratories for high-density matter physics. Recent gravitational wave observations of binary neutron star inspirals and mergers have opened new avenues for probing matter under such extreme conditions. Postmerger remnants, being hotter and more dynamic than cold pulsars, provide complementary insights.

With next-generation detectors such as the Einstein Telescope and Cosmic Explorer, multi-messenger astrophysics - combining gravitational waves, electromagnetic signals, and neutrinos - will play a central role in constraining the dense-matter equation of state, exploring extreme gravity, and understanding heavy-element nucleosynthesis. Binary neutron star mergers also act as “standard sirens” for direct cosmological distance measurements, offering an independent path to determining the Hubble constant.

The school will address the thermal history of the Universe after its first second, including the quark–hadron transition, neutrino and neutron decoupling, and the microphysics linking early-universe particle interactions to cosmological observables. It will explore the Hubble tension and theoretical proposals for its resolution, including connections between modified gravity, primordial magnetic fields, and compact object mergers. Further topics will include the future of gravitational wave astronomy, the science goals of next-generation detectors, and the role of primordial black holes as potential dark matter candidates or seeds of early galaxy formation. This interdisciplinary program will connect astrophysics, cosmology, and particle physics, offering participants a unified perspective on fundamental questions about the Universe. 

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