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Formation and Evolution of Protoplanetary Disks

Appelgren, Johan LU (2019) In Lund Observatory Examensarbeten ASTM31 20191
Lund Observatory
Abstract
A star forms with a surrounding protoplanetary disk after the collapse of a molecular cloud core. Subsequently, over a period of several Myr this protoplanetary disk of dust and gas is accreted onto the host star. We model the formation and evolution of such a protoplanetary disk using a one-dimensional numerical model. We find that disks form on a time scale of less than 1 Myr and that the size and mass of the disk at the end of formation depend on the angular momentum of the molecular cloud core, which may explain the large diversity in observed disk masses and radii. The initial disk size subsequently sets its viscous lifetime. In order for the star to accrete the disk within 5 Myr we find that disks need to form very compact (within... (More)
A star forms with a surrounding protoplanetary disk after the collapse of a molecular cloud core. Subsequently, over a period of several Myr this protoplanetary disk of dust and gas is accreted onto the host star. We model the formation and evolution of such a protoplanetary disk using a one-dimensional numerical model. We find that disks form on a time scale of less than 1 Myr and that the size and mass of the disk at the end of formation depend on the angular momentum of the molecular cloud core, which may explain the large diversity in observed disk masses and radii. The initial disk size subsequently sets its viscous lifetime. In order for the star to accrete the disk within 5 Myr we find that disks need to form very compact (within about 3 au).
% We also find that there is no single relation between the stellar accretion rate and the disk mass. Instead, at a given accretion rate the corresponding disk mass will depend on the initial conditions of the cloud core.
Dust disk lifetimes are investigated assuming that particles sizes are held constant by the combined effects of coagulation, bouncing and fragmentation. For dust sizes of 0.1 and 0.01 cm we find that the dust disk drains significantly faster than the gas disk, having lifetimes that are at least 2-3 Myr shorter than the 5 Myr simulation. For 0.001 cm sized dust, the dust disk only begins to rapidly drain inwards towards the end of the 5 Myr simulation, but maintaining such small particles would require very low coagulation efficiencies in the outer disk. For these particles with fixed sizes, we find that pebbles can pile up and could form planetesimals though the streaming instability early in the disk evolution at a wide range of orbital radii. With this in mind, we also briefly look into the potential of planet formation via pebble accretion, starting with embryos placed in these streaming instability active regions. We find that giant planets cores of about 10 M$_\Earth$ can emerge after the disk formation phase has ended in a timespan of about 0.25 Myr yr for 0.1 cm sized pebble at an orbit of about 10 au. For 0.01 cm sized pebbles we find that planets are able to grow to masses from a few Mars masses to a few Earth masses, both in the inner disk ( < 5 au) and the outer disk ( < 10 au). (Less)
Popular Abstract (Swedish)
De första idéerna om hur planeterna i solsystemet bildades härstammar från den franske filosifen René Descartes på 1600-talet. Vad räknas solsystemet som - är denna teori bara kring planeterna eller hela solsystemet och dess komponenter?)
Den teori som forskare tror på idag kan spåra sitt ursprung till mitten av 1700-talet, från den svenske forskaren Emanuel Swedenborg och den tyske filosofen Immanuel Kant. Deras hypotes kallas Solnebulosan. Den föreslår att solens planesystem bildades från en disk av gas och stoft som omringade solen när den var ung.

På över 250 år har Swedenborg och Kants teori, i grunden, förändrats förvånandsvärt lite. Vi tror fortfarande att planeter bildas från en disk av damm och stoft, vilket idag kallas för... (More)
De första idéerna om hur planeterna i solsystemet bildades härstammar från den franske filosifen René Descartes på 1600-talet. Vad räknas solsystemet som - är denna teori bara kring planeterna eller hela solsystemet och dess komponenter?)
Den teori som forskare tror på idag kan spåra sitt ursprung till mitten av 1700-talet, från den svenske forskaren Emanuel Swedenborg och den tyske filosofen Immanuel Kant. Deras hypotes kallas Solnebulosan. Den föreslår att solens planesystem bildades från en disk av gas och stoft som omringade solen när den var ung.

På över 250 år har Swedenborg och Kants teori, i grunden, förändrats förvånandsvärt lite. Vi tror fortfarande att planeter bildas från en disk av damm och stoft, vilket idag kallas för en protoplanetär disk.

Åratal av forskning kring ämnet har avslöjat att det finns flertalet utmaningar att överkomma för att bygga planeter - där många av dessa utmaningar överkommits. En metod som har varit vanlig att använda är att man utgår från en färdigbildad disk designad så att den innehåller tillräckligt mycket gas och stoft för att kunna bilda solsystemet. Innan vi kände till fler planetsystem än vårt eget var detta kanske inte en dum idé, men idag känner vi till tusentals, och upptäcker nya i en rasande fart. Genom dessa upptäckter har det visat sig att vårt solsytem faktiskt skiljer sig en hel del ifrån många av dessa andra planetsystem. En model baserad på solsystemet kan således anses vara bristande i grunden.

Utgår man ifrån en färdigbildad disk tar man inte hänsyn till det stadie då stjärnan och disken bildas. Stjärnor bildas nämligen ifrån stora moln av gas och stoft som kollapsar under sin egen gravitation. I denna process kommer en del av gasen och stoftet att landa så att det bildar en disk runt stjärnan, och det är detta som bildar den protoplanetära disken.

I detta projekt vill vi utveckla en modell där vi inkulderar hur stjärnan och den protoplanetära disken bildas. Genom att använda datorsimuleringar kommer vi undersöka hur det kollapsande molnets egenskaper, så som rotation och massa, påverkar hur disken bildas och utvecklas. Vi vill även undersöka ifall detta kan påverka hur planeter bildas. (Less)
Please use this url to cite or link to this publication:
author
Appelgren, Johan LU
supervisor
organization
course
ASTM31 20191
year
type
H2 - Master's Degree (Two Years)
subject
keywords
protoplanetary disk, protoplanetary disk formation, protoplanetary disk evolution, planet formation
publication/series
Lund Observatory Examensarbeten
report number
2019-EXA148
language
English
id
8981106
date added to LUP
2019-06-10 12:54:53
date last changed
2019-06-10 12:54:53
@misc{8981106,
  abstract     = {A star forms with a surrounding protoplanetary disk after the collapse of a molecular cloud core. Subsequently, over a period of several Myr this protoplanetary disk of dust and gas is accreted onto the host star. We model the formation and evolution of such a protoplanetary disk using a one-dimensional numerical model. We find that disks form on a time scale of less than 1 Myr and that the size and mass of the disk at the end of formation depend on the angular momentum of the molecular cloud core, which may explain the large diversity in observed disk masses and radii. The initial disk size subsequently sets its viscous lifetime. In order for the star to accrete the disk within 5 Myr we find that disks need to form very compact (within about 3 au).
% We also find that there is no single relation between the stellar accretion rate and the disk mass. Instead, at a given accretion rate the corresponding disk mass will depend on the initial conditions of the cloud core.
 Dust disk lifetimes are investigated assuming that particles sizes are held constant by the combined effects of coagulation, bouncing and fragmentation. For dust sizes of 0.1 and 0.01 cm we find that the dust disk drains significantly faster than the gas disk, having lifetimes that are at least 2-3 Myr shorter than the 5 Myr simulation. For 0.001 cm sized dust, the dust disk only begins to rapidly drain inwards towards the end of the 5 Myr simulation, but maintaining such small particles would require very low coagulation efficiencies in the outer disk. For these particles with fixed sizes, we find that pebbles can pile up and could form planetesimals though the streaming instability early in the disk evolution at a wide range of orbital radii. With this in mind, we also briefly look into the potential of planet formation via pebble accretion, starting with embryos placed in these streaming instability active regions. We find that giant planets cores of about 10 M$_\Earth$ can emerge after the disk formation phase has ended in a timespan of about 0.25 Myr yr for 0.1 cm sized pebble at an orbit of about 10 au. For 0.01 cm sized pebbles we find that planets are able to grow to masses from a few Mars masses to a few Earth masses, both in the inner disk ( < 5 au) and the outer disk ( < 10 au).},
  author       = {Appelgren, Johan},
  keyword      = {protoplanetary disk,protoplanetary disk formation,protoplanetary disk evolution,planet formation},
  language     = {eng},
  note         = {Student Paper},
  series       = {Lund Observatory Examensarbeten},
  title        = {Formation and Evolution of Protoplanetary Disks},
  year         = {2019},
}