ITC Colloquium - Jorge Penarrubia (U Edinburgh) and Kishalay De (Caltech)


Thursday, October 8, 2020, 11:00am to 12:00pm


  1. Jorge Penarrubia (U Edinburgh)  "Impact of `dark' microhaloes on the dynamics of stars & planetary systems"

    In the current cosmological paradigm (Cold Dark Matter, CDM), galaxies like the Milky Way are teeming with dark matter substructures with masses as low as that of Earth (M~10^{-6} Msol), or even of asteroids (M~10^{-12} Msol). These objects do not contain baryons, and can only be detected through their gravitational attraction. However, to date it remains unclear to what extent such puny microhaloes affect the motion of visible objects.
    In this talk, I will introduce a Monte-Carlo N-body method that mimics the gravitational forces induced by a large population of dark substructures with known mass and size functions, and show that the tidal field of CDM haloes is dominated by the smallest (and most abundant) microhaloes.
    In view of this result, I will discuss the possibility to use Gaia observations of loosely-bound objects, such as co-moving stars and Oort clouds, to investigate the energy scale at which DM deviates from a perfect fluid and put constraints on a large range of particle candidates.
  1. Kishalay De (Caltech) "The faintest thermonuclear supernovae and the explosive fates of helium accreting white dwarfs"

    Accreting white dwarfs with He-rich companions provide crucial insights into several key issues in modern astrophysics. While they have also been long proposed as progenitors of Type Ia supernovae from sub-Chandrasekhar mass white dwarfs, observations of the majority of Type Ia supernovae appear inconsistent with explosive He shell burning scenarios except for the faintest and fastest thermonuclear supernovae that have been difficult to systematically uncover in previous time domain surveys. In this talk, I will present results from a systematic search for these elusive thermonuclear transients with the largest volume-limited sample of supernovae constructed till date using the Zwicky Transient Facility optical time domain survey. I will discuss observational evidence that suggests that He shell explosions are realized in nature over a broad range of white dwarf core and shell masses -- ranging from peculiar Type Ia supernovae to the faintest class of 'Ca-rich' transients. Together, a systematic exploration of these unique explosions opens up a completely new window into the explosive fates of He-accreting white dwarfs and progenitors of Type Ia supernovae. 
See also: Colloquium, 2020-21