EMRI+TDE=QPE: Star-Disc Interaction around Massive Black Holes and Quasi-Periodic Eruptions

Quasi-periodic eruptions (QPEs) are an emerging class of high amplitude bursts of X-ray radiation, repeating on a hours-day timescale, recently discovered near the central supermassive black holes (SMBHs) of a few low-mass galaxies. I will briefly review our current theoretical understanding of QPEs, and will focus on a scenario involving a main-sequence star repeatedly colliding with an accretion flow feeding the SMBH. I will demonstrate how this model naturally reproduces the observed period, luminosity, emission temperature, duration, occurrence rate of QPEs, as well as the association between QPEs and other types of transients occurring around SMBHs. I will also discuss the implications of the observations and of our model for probing the dynamics around SMBHs, accretion physics around SMBHs, the rate of extreme mass ratio inspirals (EMRIs), and the discovery prospects of related repeating nuclear transients. 420 The progenitors of Type Ia Supernovae: a clear-cut case for the Lunar Gravitational Wave Antenna European Southern Observatory 2 INAF-OAPD 3 GSSI Despite of the key role of Type Ia Supernovae in cosmology and after decades of research, the nature of their progenitors remains unclear. None of the results obtained so far is sufficiently conclusive and, in some cases, the findings appear to be even in contradiction. Moreover, observations have shown that about 30% of the discovered SNe Ia largely deviate from the properties of ‘normal’ thermonuclear events, such as peak luminosity, light curve morphology and spectral features. The rising era of GW astronomy opens a new avenue for obtaining independent and direct insights to the SN~Ia progenitors’ nature, which remains one of the burning, open questions in modern astrophysics. In my talk I will present the problem and its possible solution in connection to the foreseen GW detectors in the deci-Hz region. In particular, I will describe and discuss the case of the Lunar Gravitational Waves Antenna, which carries the promise of answering this fundamental question.