Sad news today from Simon Portegies Zwart, who wrote the following orbituary:
It is with great sadness that I have to inform you of the passing away of Sverre Aarseth on 28 December this year after 90 two-body orbits. Sverre Johannes Aarseth was born on July 20, 1934, in Norway.
Sverre was a student of Fred Hoyle, and later became the supervisor of Douglas Heggie and Elena Terlevich at the University of Cambridge’s Institute of Astronomy. He pioneered computational astrophysics, developing the NBODY family of codes that revolutionized our understanding of planet formation, stellar clusters, the dynamics of black holes, and galaxy clusters. His work laid the foundation for numerous advancements in dynamical astronomy, earning him the prestigious Brouwer Award in 1998.
His commitment to open science was evident long before the concept of open-source software became popular, as he freely distributed and supported his codes. Generations of astronomers have benefited from Sverre’s codes. In recognition of his contributions, asteroid 9836 Aarseth (1985 TU) was named in his honor. Fittingly, Sverre is currently observable between Virgo and Lyra, a celestial tribute to his lasting impact on the field.
Beyond his scientific pursuits, Sverre was an avid mountaineer and accomplished chess player. He earned the title of International Master for Correspondence Chess in 1981. The astronomical community celebrated his 80th birthday in Sexten Italy in 2014, where we climnbed the Tre Cime di Lavaredo (also called der Drei Sinnen, a pathetic small mountain for Sverre), almost missing his afternoon talk.
Generations of astronomers were entertained by his vivid stories of meeting tigers (in the wild), racing cars, and stormy mountain top sleep-overs. His lively personality, humor, and groundbreaking work will be remembered fondly. As he ascends to a higher orbit, we will cherish the memory of his vibrant personality, captivating stories, and the invaluable codes he wrote. His legacy will continue to inspire future generations of astrophysicists, much like the celestial bodies he spent his life studying.
We have been lucky to have orbited Sverre.
I couldn’t have hoped for a better, kinder, more understanding supervisor! He’ll be sorrowly missed!
Sverre was just great! He will be missed.
Count me among the beneficiaries of Sverre’s codes. I had the good fortune of visiting Cambridge in 1981-82, where I received copies of NBODY1 and NBODY2 directly from the master. Sverre was incredibly generous with his time in explaining how the codes worked, although he was mock-appalled when I translated them into more structured dialects of FORTRAN. Simply put, Sverre was an original.
He told me some of those stories over tea at the IOA back in the 2000s. We both had a love of the mountains, so I listened to his stories of climbing in remote locations with rapture. I’ve been known to repeat some of them to this day, like the one where he froze his foot on some mountain in the Caucuses and flew back to England before going to the hospital.
I am very sad to learn of his passing. He was always very generous with his time and kept an open mind to new applications of his methods and codes. A pioneer, that has to be underscored. To think it all started with punch cards ..
I am deeply indebted to Sverre Aarseth. He was not only a collaborator but also a close mentor throughout my whole scientific life. I miss him so very much.
My work on the initial distribution functions of binary systems would have been entirely impossible without Sverre Aarseth’s Nbody codes. I am deeply thankful to Sverre for his kindness and generosity and patience for spending many an hour with teaching me stellar dynamics and on discussions of the above, and for extending and tailoring his immensely important computer codes to allow the calculations I needed to do. He always kept me updated personally and we spoke many times, lastly very regularly, when he still could over skype and zoom. I will be forever grateful to this fit giant of a Norwegian who migrated to Cambridge to do his PhD under Fred Hoyle, and ultimately his Nbody work there. In 2012 he once complained to me that he had become “merely a footnote in the history of science” when I wrote footnote 2 in the invited “The Dark Matter Crisis: Falsification of the Current Standard Model of Cosmology”. The footnote explained that Sverre Aarseth was the first to have done a cosmological structure formation simulation, and why he quickly left that field again. Whilst I was a PhD student at the IoA in Cambridge, Sverre very often came to me at coffee kindly asking me how I was and then explaining his most recent advances. On his first approach he jokingly introduced himself to me with “I am famous, who are you?”, something he liked to do with others too. Once, in mid 1992, he approached me in a most excited state while I was struggling with a cookie that had partially melted and fallen into my coffee cup and he dragged me to his famous office which was adjacent to where the coffee was being served and “locked me in”. He proceeded to explain to me over some hours the discovery of how to implement chain regularisation into the Nbody code (Mikkola & Aarseth, 1993CeMDA..57..439M). While I had no clue about what he was saying then and was somewhat initially preoccupied with that cookie (and I was merely counting stars in any case at that time), it became clear to me that he had participated in an extraordinarily important discovery in mathematics which improved his Nbody codes dramatically, making my later work on binaries in star clusters much more possible. This development just so happened to occur when the first high-resolution imaging and speckle interferometry observations of nearby star-forming regions done in the early 1990s turned up the unexpected result that nearly all pre-main sequence stars there are binaries. The hypothesis I formulated on hearing these results at a conference in Atlanta was that the binaries break up in embedded clusters, but this needed to be shown by Nbody calculations. This is where the new chain regularisation came into play. Sometimes different research developments and people conspire to interfere constructively at just the right time to allow interesting progress. I am deeply indebted to have witnessed such a magical and very special time in science, and I wish I could be there again with Sverre. He also often listened to me about my ideas and troubles and always provided encouragement. He was always there, either in person or on email. Any time with him was in fact special, and especially the wine-full evenings. I am deeply thankful to Sverre Aarseth for his generosity and kindness in providing me with his support, especially during the critical early 1990s when I often visited him in Cambridge bringing bottles of German white wine with me to in turn receive “Nbody driving lessons”, a term he liked to use when teaching me how to drive his Nbody5 code. I know of no other scientist who remained so close to the ideal of solving research problems, fighting bugs relentlessly, and who was so pure and unpolitical and positively spirited. He visited me on most of my major trips and stays abroad, in so many places, and we had regular “Sverre Aarseth Xmas Glühwine Nbody meetings” at the Hoher List Observatory in Germany and later in Prague. Sverre’s adventures in the mountains and his unrelenting support of the animal world are legendary. He wrote an account of his mountaineering in “ Adventures of a Rekless Amateur” (Aarseth 2014, published by Lulu.com, ISBN-10:1291991670). The Nbody community suffered a very major loss with his passing on Dec. 28th in 2024. Alas, he is not there any longer. He will be more than missed, a beautiful era having ended. No place is the same with him being absent entirely.
Dear friends,
as part of the German amateur community, I try to explain our members astrophysics. Of course, simulation of star clusters was and is an important part of it. At first, I wrote my own code, but later I used Sverres’ nbody6. I contacted Sverre and he helped me with my first steps in that piece of software. Unfortunately, I could not use his office because of Corona.
It took some time, but now I have a good understanding how to use this codes and which pitfalls there are.
I am very glad that I got knowing him. I am deeply grateful for his support of the astronomical community and for making his code “free”.
I love Sverres old style Fortran code which is very easy to read.
Uwe Pilz.
I was also a beneficiary of Sverre’s remarkable generosity, which prompted me to pursue activities fueled by free open-source computational tools. My first interactions, circa 1987 during my PhD dissertation work on globular cluster dynamics, were about NBODY1 after it was published in the 1st edition of Binney and Tremaine’s “Galactic Dynamics.” My last message from him is from 2021, when Sverre joked about his “emeritus post-doc” status. His devotion to research and teaching with disregard for the safety of administrative duties and tenure was an inspiration to me. I learn of his passing with profound sadness, only partially tempered by my gratitude for his time and the teachings I received from Sverre, along with the charge to pass them on to the next generation. Thank you from the bottom of my heart, Sverre. You will be very sorely missed.
For those not on the MODEST mailing list, today on Jan 28 I’ve started the honor Sverre’s code with an expose in a bash jupyter notebook on https://github.com/teuben/nemo/blob/master/scripts/notebooks/aarseth.ipynb and hope to have it finished by Feb 28. Contributions welcome.