Astronomy seminars

Cosmological surveys can reveal new particles through signals hidden among astrophysical foregrounds. This talk examines axion conversion of microwave photons in magnetized galactic halos, using Planck, unWISE and ACT observations with improved component separation. It then turns to inflationary particle signatures in galaxy clustering, including a constraint on the primordial four-point amplitude from DESI galaxies and quasars. The discussion highlights both the reach of these measurements and the systematic challenges of analysing extremely large scales.

Gravitational-wave detections show an excess of binary black-hole mergers around 35 solar masses. This talk compares their mass ratios, spins and redshifts with the predictions of competing formation mechanisms. The central question is whether one astrophysical pathway can account for the observed features or whether several populations contribute to the excess.

A weak attractive interaction confined to dark matter can outweigh gravity over subgalactic distances. This talk studies its effects on collapse and stable bound structures when the force is screened beyond roughly kiloparsec scales. Delaying its onset until low cosmic density avoids early-Universe and galaxy-structure constraints. For fermionic matter, the additional attraction can support much lighter particles against degeneracy pressure; a density-triggered phase transition provides a concrete delayed-activation mechanism.

Can quantum uncertainty resolve cosmological singularities within the Wheeler–DeWitt description itself? Introducing an observer's proper time turns the problem into evolution resembling scattering in a central potential. The talk describes a smooth quantum bounce for a radiation-filled universe, with large scale-factor uncertainty, and explains why anisotropy introduces a critical attractive potential. That harder regime motivates extending the classical BKL account of singularities into quantum theory.

Lyman-alpha galaxies offer a way to map structure beyond redshift two and connect galaxy surveys with microwave-background lensing. This talk demonstrates selection from IBIS medium-band images and spectroscopic follow-up with DESI. Joint clustering measurements of these galaxies and quasars constrain bias, small-scale velocity effects and radiative-transfer contributions, testing the modelling needed for future high-redshift surveys.

Early active black holes seen by JWST, pulsar-timing evidence for a gravitational-wave background and stellar tidal disruptions probe different parts of black-hole growth. This talk presents L-GalaxiesBH, which follows black holes and their host galaxies from early formation to the present. Combining these observations constrains growth models, including the abundance of rapidly growing early objects, massive binaries nearby and elusive intermediate-mass systems.