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Lego Figure holding a lego telescope. Photo

Johan Appelgren

Doctoral student

Lego Figure holding a lego telescope. Photo

Formation and Evolution of Protoplanetary Discs


  • Johan Appelgren

Summary, in English

Protoplanetary discs and the protostars they surround are formed from the gravitational collapse of molecular
cloud cores. These discs consist primarily of gas, with a small but important dust component. The roughly
mm-sized grains that make up the dust component are the building blocks of planets. Over a timescale of up
to a few million years, the dust in protoplanetary discs is lost. Some of the dust will be locked up into
planetesimals and planets, but the majority of the decrease in the dust mass is likely caused by the radial drift
of pebbles.
In this thesis, I have studied the evolution of protoplanetary discs, with a focus on the evolution of the dust
disc through the radial drift of pebbles. I developed a numerical model that includes the formation of the disc
from a collapsing molecular cloud core, viscous evolution and photoevaporation of the gas disc, as well as the
growth and radial drift of the dust disc.
In Papers I and II, we explored the temporal evolution of the dust mass in protoplanetary discs due to radial
pebble drift using a population synthesis approach. We found that discs undergoing radial pebble drift can
sustain sufficient dust masses for long enough to explain the observed decrease in dust masses in observed
protoplanetary discs.
In Paper III, we conducted synthetic observations of discs, comparing how the total flux emitted from
protoplanetary discs evolves with their apparent size. We examined how this relationship depends on the
initial angular momentum of the cloud core from which the discs are created and on the efficiency of viscous
heating. We found that discs with high angular momentum and weak viscous heating provide the best
agreement with measurements of real discs. Additionally, we found that discs undergoing radial drift are
generally optically thin.


  • Astrophysics

Publishing year




Document type



Lund University


  • Astronomy, Astrophysics and Cosmology


  • Protoplanetary discs
  • Accretion discs
  • planet formation




  • Planet formation around young stars


  • Anders Johansen
  • Oscar Agertz


  • ISBN: 978-91-8039-898-5
  • ISBN: 978-91-8039-899-2

Defence date

14 March 2024

Defence time


Defence place

Lundmarksalen, Sölvegatan 27, Lund


  • Paola Pinilla (Doctor)