SciPost Astro. 2, 001 (2022) ·
published 17 January 2022

· pdf
Since the discovery of the accelerated cosmic expansion, one of the most
important tasks in observational cosmology is to determine the nature of the
dark energy. We should build our understanding on a minimum of assumptions in
order to avoid biases from assumed cosmological models. The two most important
functions describing the evolution of the universe and its structures are the
expansion function E(a) and the linear growth factor D_+(a). The expansion
function has been determined in previous papers in a modelindependent way
using distance moduli to typeIa supernovae and assuming only a metric theory
of gravity, spatial isotropy and homogeneity. Here, we extend this analysis in
three ways: (1) We extend the data sample by combining the Pantheon
measurements of typeIa supernovae with measurements of baryonic acoustic
oscillations; (2) we substantially simplify and generalise our method for
reconstructing the expansion function; and (3) we use the reconstructed
expansion function to determine the linear growth factor of cosmic structures,
equally independent of specific assumptions on an underlying cosmological model
other than the usual spatial symmetries. We show that the result is quite
insensitive to the initial conditions for solving the growth equation, leaving
the presentday matterdensity parameter {\Omega}_m0 as the only relevant
parameter for an otherwise purely empirical and accurate determination of the
growth factor.
SciPost Astro. 2, 002 (2022) ·
published 1 April 2022

· pdf
A planet hardly ever survives the supernova of the host star in a bound
orbit, because mass loss in the supernova and the natal kick imparted to the
newly formed compact object cause the planet to be ejected. A planet in orbit
around a binary has a considerably higher probability to survive the supernova
explosion of one of the inner binary stars. In those cases, the planet most
likely remains bound to the companion of the exploding star, whereas the
compact object is ejected. We estimate this to happen to $\sim 1/33$ the
circumbinary planetary systems. These planetary orbits tend to be highly
eccentric ($e \ {\raise.5ex\hbox{$\buildrel>\over\sim$}}\ 0.9$), and $\sim 20$\,\% of these planets have retrograde
orbits compared to their former binary. The probability that the planet as well
as the binary (now with a compact object) remains bound is about ten times
smaller ($\sim 3\cdot 10^{3}$). We then expect the Milky way Galaxy to host
$\ {\raise.5ex\hbox{$\buildrel<\over\sim$}}\ 10$ xray binaries that are still orbited by a planet, and $\ {\raise.5ex\hbox{$\buildrel<\over\sim$}}\ 150$
planets that survived in orbit around the compact object's companion. These
numbers should be convolved with the fraction of massive binaries that is
orbited by a planet.