The formation of stars and planets
Werbung
Lecture “Planet Formation” Topic: Overview of the standard model of planet formation Lecture by: C.P. Dullemond Standard Model 1. A star is formed, surrounded by a disk of dust and gas 2. The dust particles coagulate forming ever larger dust aggregates, rocks, boulders 3. ...some miracle happens... and sizes of >km are reached (as we will see later, this is a strange thing) 4. These planetesimals gravitationally interact leading to „runaway growth“. A „planetary embryo“ is formed (~ 1000 km) 5. The embryo accretes further planetesimals and grows 6. Nearby embryos collide and merge to form a rocky planet 7. IF the planet continues to grow to ~ 10 Mearth, then it will attract gas from the disk and form a gas giant planet. Birthplace of stars: Molecular Clouds Ophiuchus Giant Molecular Cloud (by Loke Tan) Birthplace of stars: Molecular Clouds Ophiuchus Giant Molecular Cloud (by Loke Tan) Forming stars from Molecular Clouds M. Bate Exeter UK MOVIE Very dense Molecular Cloud: very aggressive star formation ‘Isolated’ Star Formation M.Hogerheijde1998, after Shu et al. 1987 Observed protoplanetary disks Credit: NASA Observed protoplanetary disks HST image of AB Aurigae by Carol Grady The long road from dust to planets First growth phase Final phase Gravity keeps/pulls bodies together Aggregation (=coagulation) 1m 1mm 1m 1km Gas is accreted 1000km Covers 13 orders of magnitude in size = 40 (!!) orders of magnitude in mass Immanuel Kant already understood it! “Der Anfang der sich bildenden Planeten ist nicht allein in der Newtonschen Anziehung zu suchen. Diese würde bei einem Partikelchen von so ausnehmender Feinigkeit gar zu langsam und schwach sein. Man würde vielmehr sagen, dass in diesem Raume die erste Bildung durch den Zusammenlauf einiger Elemente, die sich durch die gewöhnlichen Gesetze des Zusammenhangs vereinigen, geschehe, bis derjenige Klumpen, der daraus entstanden, nach und nach so weit angewachsen, dass die Newtonsche Anziehungskraft an ihm vermögend geworden, ihn durch seine Wirkung in die Ferne immer mehr zu vergrößern.” Aus: Immanuel Kant „Allgemeine Naturgschichte und Theorie des Himmels“ (1755) http://www.deutschestextarchiv.de/book/show/kant_naturgeschichte_1755 (thanks to Willy Kley for pointing me to this amazing citation) Immanuel Kant already understood it! “The start of the formation of a planet is not to be sought only in the Newtonian attractive forces. They would, for such small particles, be too slow and too weak. One would more say that the first phases of growth take place through the collision of elements that aggregate through the usual laws of cohesion, until these clumps eventuell have grown so much, that the Newtonian attractive forces, with their long range of influence, spur their growth ever further.“ English translation from Immanuel Kant „Allgemeine Naturgschichte und Theorie des Himmels“ (1755) http://www.deutschestextarchiv.de/book/show/kant_naturgeschichte_1755 (thanks to Willy Kley for pointing me to this amazing citation) So, what is this „cosmic dust“? • Difficult to know because we have no method (yet) of collecting interstellar dust • But there is „interplanetary dust“ from evaporating comets. • These Interplanetary Dust Particles are dust aggregates Collected from the stratosphere with a U2 airplane Particles move... ...because protoplanetary disks are turbulent, and turbulent gas stirs up the dust. ...and because of drift (more on that during the lecture). What happens when they collide? Numerical models Small sizes: a = 10 μm MOVIE Paszun & Dominik 2009 See also Wada et al. 2009, Suyama, Wada & Tanaka 2008 What happens when they collide? Laboratory experiments MOVIE From the laboratory of J. Blum, Braunschweig Movie from NASA Next phase: Growth by gravity Thanks to Sean Raymond for lending me his movie Next phase: Growth by gravity MOVIE Thanks to Sean Raymond for lending me his movie Collision of two planets or moons ARTIST IMPRESSION Image credit: Don Davis Collision of two planets or moons MOVIE Asphaug & Reufer 2013 http://vimeo.com/50778094 Accretion of smaller bodies onto big ones MOVIE Stewart (2011) http://www.fas.harvard.edu/~planets/sstewart/Movies.html On to final planets Figure from C. Mordasini‘s lecture Formation of gas giants (if sufficient gas is present) Figure from C. Mordasini‘s lecture Formation of gas giants (if sufficient gas is present) Artist‘s impression by Moonrunner Design National Geographic http://science.nationalgeographic.com/science/wallpaper/planet-formation.html Alternative GGP formation scenario Gravitational instabilities in the disk Model by Thomas Quinn http://www.psc.edu/science/quinn.html Alternative GGP formation scenario Gravitational instabilities in the disk Model by group of Richard Durisen http://hydro.astro.indiana.edu Planet-disk interaction & migration MOVIE Kley & Nelson (2012) Annual Reviews of Astronomy & Astrophysics http://vimeo.com/45256035 Planet formation synthesis models MOVIE Mordasini et al. (2009)
