Calendar

The interaction of the shock waves originated from supernova explosions with the circumstellar medium provides crucial information on the physics of shock heating. Astrophysical shocks at all scales, from those in the heliosphere up to the cosmological shock waves, are typically collisionless and electrons, protons, and ions are expected to be heated at different temperatures. Although optical observations of Balmer-dominated shocks in young SNRs showed that the post-shock proton temperature is higher than the electron temperature, the actual dependence of the post-shock temperature on the particle mass is still widely debated. We tackle this longstanding issue through the analysis of deep multi-epoch and high-resolution observations of SN 1987A, made with the Chandra X-ray telescope. We study the observed spectra in close comparison with a dedicated full 3-D hydrodynamic simulation. The simulation is able to reproduce self-consistently the whole broadening of the spectral lines of many ions altogether. We could therefore measure the post shock temperature of protons and selected ions in the shocked circumstellar medium. We found that the ion to proton temperature ratio is always significantly higher than one and increases linearly with the ion mass for a wide range of masses and shock parameters. This provides information about the heating processes in collisionless shocks.

Very Hot Super-Earths with an Atmosphere: A Model Explaining Their Paradoxical Existence

The aim of this research is to constrain the interior structures and evolutions of hot super-Earths, particularly that of 55 Cancri e. Herewith, we propose an alternative model for the paradoxical nature of small, hot super-Earths with atmospheres. Our model does not require these bodies to contain large quantities of ices in order to account for their low densities, which has been a subject of dispute considering their high surface temperatures and the potentially strong internal heat processes such as tidal flexing or radiogenic heating. The first aspect of our research involved calculating the total H₂ reservoir in 55 Cancri e which is ~ 2×10²³ kg (0.04 M_⨁). We then encountered a theoretical enigma since the UV and X-Ray induced mass loss should have been strong enough to evaporate the atmosphere billions of years ago, which is inconsistent with astronomical data showing a currently plentiful atmosphere. This issue can be completely avoided by showing that for a tidally locked setup, the mass loss rates on the night-side are negligible thus allowing the planet to maintain a H₂-rich atmosphere above half its surface. In the case of 55 Cancri e, it became tidally locked approximately 50 ± 250 Myrs after it formed implying that from that moment onwards the radius and mass of the body changed negligibly. Prior to this time mass loss rates were very strong and approximately homogeneous which when modelled, showed that 55 Cancri e was born as a Neptunian-or-Jovian-type exoplanet. Finally, we propose that the bimodal distribution in exoplanet radii may be the result of two different evolutionary paths; one where a super-Earth loses all of its atmosphere before it becomes tidally locked (resulting in the peak at ~ 1.3 R_⨁), and the other when super-Earths become tidally locked before losing their atmosphere allowing them to maintain it (resulting in the other peak at ~ 2.4 R_⨁).