Seminars

HEAVYMETALs from Binary Neutron Star Mergers

The incredible density, gravity, and electromagnetic field strengths of neutron stars (NS) make them laboratories for physics under extreme conditions. But probing these exotic objects is difficult. With the 2017 gravitational wave detection of a NS-NS merger, the landscape changed, and we can now get high-quality spectra of the decompressed neutron-rich matter emerging from the collision.

Kilonovae are challenging: the phenomenon is short-lived, requiring rapid follow-up with large telescopes, the outflow is heavy element-dominated making it extremely demanding to model, and the merger itself covers a huge dynamic range and involves complex nuclear physics. To interpret the spectra we require new atomic data, which does not yet exist for most of the heavy elements.

This talk outlines the properties of binary neutron star mergers, observations of kilonovae, and the experimental work underway in the Spectroscopy Group at UCD to generate new spectra of ions to facilitate interpretation of some of their observable properties and understanding of their underlying physics.

Intranuclear herpes DNA ejection induces robust mechanoprotection of nucleus integrity required for viral genome replication

Maintaining nuclear integrity is essential to cell survival when exposed to mechanical stress. Herpesviruses, like most DNA and some RNA viruses, put strain on the nuclear envelope as hundreds of viral DNA genomes replicate and viral capsids assemble. It remained unknown, however, how nuclear mechanics is affected at the initial stage of herpesvirus infection—immediately after viral genomes are ejected into the nuclear space—and how nucleus integrity is maintained despite an increased strain on the nuclear envelope. With an AFM force mapping approach on cell-free reconstituted nuclei with docked herpes simplex type 1 (HSV-1) capsids, we explored the mechanical response of the nuclear lamina and the chromatin to intranuclear HSV-1 DNA ejection into an intact nucleus. We discovered that chromatin stiffness, measured as Young’s modulus, is increased by ~14 times, while nuclear lamina underwent softening. This suggests increased chromatin compaction, induced by non-random interactions between viral DNAs and the cell chromosome, resulting in increased nucleus stiffness. Stiffening of chromatin, which is tethered to the lamina meshwork, helps to maintain nuclear morphology. At the same time, increased lamina elasticity, reflected by nucleus softening, acts as a “shock absorber” dissipating the internal mechanical stress on the nuclear membrane (located on top of the lamina wall) and preventing its rupture. This data provides a striking demonstration of mechanoprotection of nucleus integrity induced by herpesvirus infection, required for viral genome replication.

Supernova frontier: beyond standard stellar demises

Quantum Darwinism

Measuring cellular forces and currents with the FluidFM