Center for Astronomy Heidelberg - Institute of Theoretical Astrophysics (2025)

Protoplanetary disks

The dusty gas disks surrounding many young stars are the left-overs ofthe star formation process. These disks are often called"protoplanetary disks" because it is believed that they are thebirthplaces of planets and planetary systems. Our own Solar System wasonce formed from such a disk surrounding the young sun, 4.567 billionyears ago. With powerful telescopes such disks can be observed andstudied around young stars, and we can thus get a glimpse of what ourown pre-planetary solar system looked like at its birth.

In my research I study the structure and evolution of protoplanetarydisks using numerical modeling, and the comparison of these models toobservations. This research involves the study of their viscousevolution and the transport processes happening inside of these disks(e.g. Dullemond, Natta & Testi 2006, Visser& Dullemond 2010). It also involves studying their detailedstructure, in particular the temperature structure (the warm surfacelayer, cool interior, internal heat production, etc, see e.g. Dullemond & Dominik 2004a,Kamp & Dullemond 2004,Min, Dullemond, Kama & Dominik Icarus, submitted as ofNov 2010), which iscomputed using radiative transfer calculations (see my software website for more information about my radiative transfer tools). Anotherimportant aspect that I am interested in is the photoevaporation ofthese disks by the EUV, FUV and X-ray radiation from the star itself(Gorti, Dullemond & Hollenbach 2009).

Using my radiative transfer codes I have also been involved in many observationalcampaigns: To interpret observations of protoplanetary disks and possibly their envelopes in terms of disk models. Most of this work is in fact carried out by my collaborators,who use my codes (RADMC, RADMC-3D) to interpret their data(e.g. Pontoppidan et al. 2007a and 2007b,Andrews et al. 2009and 2010and many more).

Dust coagulation in disks

What originally started as part of my research on disk structuregradually became my new main field of research: the growth of dustgrains in protoplanetary disks due to the process of aggregation (alsooften called coagulation). The original goal was to understand how theopacities change over time in protoplanetary disks, and to be able tounderstand the wealth of solid state features and feature shapes seenin emission in infrared spectra of these disks (ISO, Spitzer, VLT,Keck, etc). We developed models of dust coagulation which we then insert into our radiative transfer tools to make synthetic spectraand images, which can then be compared to observations (early work: Dullemond & Dominik 2005,20042008,Dominik & Dullemond 2008)

However, dust growth is also the very first step in the process ofplanet formation. By 2006 this became the main focus of this research,and my students basically took charge of this. Firstly, FrithjofBrauer managed to design a full-disk-scale dust coagulation modelingcode that is able to evolve the dust throughout the disk including thefragmentation (Brauer,Dullemond & Henning 2008), something which I did not manage todo efficiently in my 2005 paper. He also found a way to overcomethe dreaded "meter size barrier" by trapping particles in a pressure trap (Brauer, Henning & Dullemond 2008).

Subsequently, Til Birnstiel improved Frithjof's model and merged itwith a disk evolution model (Birnstiel,Dullemond & Brauer 2009). Now the model is (almost) complete:it is very efficient (using a fully implicit integration method), itincludes radial drift and mixing as well as growth andfragmentation. In addition to this, he developed semi-analytic modelfits to his results, which can be useful for other modelers ( Birnstiel, Ormel& Dullemond 2010), and applied his model to millimeter wavedata of disk (Birnstiel,Ricci, Trotta, et al. 2010).

At the same time, Andras Zsom worked with the Braunschweig laboratorygroup to develop a new experiment-based dust coagulation kernel(Güttler, Blum, Zsom et al. 2010). It is the first timethat a dust coagulation kernel has been constructed that is basedon the last 10 years of laboratory collision experiments, and thisis thus a major step forward. However, as a result of thiswork they found a new barrier to growth: the "bouncing barrier"(Zsom, Güttler et al. 2010). At the moment we do not yetunderstand how Nature is apparently able to overcome this barrier.

From planetesimals to planets

The work on dust coagulation has led us to ask the question howthe next step proceeds: How are rocky planets formed from swarmsof planetesimals? Chris Ormel, a Humboldt postdoctoral Fellow linked to our group, has developed an ingenious new methodfor modeling this problem. It is a Monte Carlo method thatcarefully deals with the transition from runaway growth tooligarchic growth (Ormel, Dullemond & Spaans 2010). This method is particularly powerful in that it can span a huge range in planetesimal size, by use of a clever grouping method.

We are currently moving more and more in this (for us new)direction, and we have the ultimate goal of modeling rockyplanet formation all the way from dust to planets. In thenext few years I hope to be able to report on many newresults in this area.

Radiative transfer

I spend some amount of my time on developing radiative transfertools. This is not really my "research" field. It is meant as acrucial tool to link our models to direct observations of the objectswe study. So, to ensure also in the future a smooth linkeage betweenour models of disks and dust on the one hand and direct observationsof our objects on the other hand, I spend time on updating my radiativetransfer tool set.

It has turned out, however, that many other scientists also haveinterest in using these tools. I have therefore decided that I spend considerable effort in making these tools easy-to-use andwell-documented, and publically available. I see this as a serviceto the community.

Collaboration with others at the ZAH

Planet formation is strongly linked to the process of star formation.At the ITA there is a strong expertise on this topic in the starformation groupof Ralf Klessen. For this reason, and because of my expertise in3-D radiative transfer, I collaborate strongly with his star formationgroup.

I am also setting up a collaboration with RainerSpurzem on N-body modeling of planetesimals and planets duringplanet formation.

I hope to be setting up more collaborations with people at the ZAH in themonths/years to come.

Responsible: Cornelis Petrus Dullemond, last modification Mar/17/2013 18:29 CET