Quantifying neutrino-emitting blazars: beaming and jet power

Special Colloquium
Dr. Sasha Plavin
SCHEDULED
Black Hole Initiative, Harvard University

Increasing numbers of high-energy neutrinos coming from blazars are being detected, but data sparsity makes it challenging to quantitatively describe each source individually. In this talk, we present the results of modeling the distribution of a bright blazars sample, taking their geometry and observed radio and neutrino properties into account. This lets us constrain the contribution of all blazars to high-energy neutrino flux, to evaluate the effects of relativistic beaming, and to estimate hadrons contribution to the total jet power.

The observational revolution of planet forming disks

Special Colloquium
Dr. Nienke van der Marel
SCHEDULED
Leiden University

Structures such as gaps and rings in ALMA observations of protoplanetary disks have long been hailed as signposts of planet formation. However, a direct link between exoplanets and protoplanetary disks remained hard to identify. Recent work has shown that gapped disks retain high millimeter-dust masses up to at least 10 Myr, whereas the majority of disks is compact and decreases its dust mass rapidly. This can be understood when considering dust evolution, where dust traps prevent radial drift in the gapped disks. The fraction of gapped disks shows a stellar mass dependence, and I propose a scenario linking this dependence with that of giant exoplanet occurrence rates. It is shown that there are enough exoplanets to account for the observed disk structures if gapped disks are caused by exoplanets more massive than Neptune, under the assumption that most of those planets eventually migrate inwards. On the other hand, the known anti-correlation between transiting super-Earths and stellar mass implies those planets must form in the compact disks, consistent with those exoplanets forming through pebble accretion in drift-dominated disks. I will demonstrate some of the latest insights on rocky planet formation in compact disks, as well as new insights on gas giant planet formation in larger gapped disks. Finally, I will show that dust traps and radial drift may play a crucial role in regulating the chemical composition of disks, which sets the C/O ratio of exoplanet atmospheres as traced in the coming years with the James Webb Space Telescope.

Cosmology with Gravitational Wave Sirens

Main Colloquium
Prof. Dr. Tessa Baker
SCHEDULED
University of Portsmouth

The first eight years of direct gravitational wave detection have had a huge impact not only on astrophysics, but also on cosmology and fundamental physics. Central to these developments have been Sirens, gravitational wave sources for which we can measure both distances and redshifts. The most spectacular kind of sirens are multimessenger events like the binary neutron star merger GW170817, with both gravitational wave and electromagnetic counterparts. However, these represent only a tiny fraction of all gravitational wave events. So are all the other gravitational wave events useless, from a cosmology perspective? In this talk I'll introduce the alternative Dark Sirens method, which enables us to extract cosmology from regular, non-counterpart gravitational wave events. I'll explain how this technique can be used to obtain an independent measurement of the Hubble constant, and also to test the laws of gravity operating on the largest scales. I'll describe some subtleties that require careful handling, (hopefully!) convince you that we can overcome them, and show the latest results obtained from gravitational wave detections to date.