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					Recipes for the
Cosmic Cocktail
                      “Space is an enigma”:                                                   PHYSICS & ASTRONOMY_Personal Portrait
                      Sadegh Khochfar wanted
                      to be an astrophysicist
                      for as long as he can recall.




                                                      A pile of astronomy books and a telescope in his childhood
                                                      bedroom. Space cast its spell on Sadegh Khochfar at an early
                                                      age – and he is still captivated today. The 37-year-old now
                                                      heads a Max Planck research group at the Garching-based Max
                                                      Planck Institute for Extraterrestrial Physics, where he is at
                                                      least as successful at piecing together the components of the
                                                      universe as he was at mixing cocktails as a student.

                                                      TEXT ALEXANDER STIRN




                                                      S
                                                                 adegh Khochfar knows the            headed an eight-member research group
                                                                 secret to making a good caipi-      there that explores the emergence and
                                                                 rinha – if not the best. It’s the   development of galaxies. It deals with
                                                                 ratio of limes to brown sug-        such questions as why the universe
                                                                 ar. But not only does the           looks the way we see it today, how the
                                                      quantity have to be right, but also the        supermassive black holes form that are
                                                      sequence: cut the limes, sprinkle the          found at the center of most galaxies,
                                                      sugar on them, and only then do you            and which growth phases these struc-
                                                      mash them. Only in this way can the            tures go through on the path from baby
                                                      sugar bind with the essential oils in          galaxy to mature stellar system.
                                                      the peel, allowing the caipirinha to de-
                                                      velop its full flavor.                         FREEDOM TO DREAM UP
                                                           The 37-year-old should know. For          CRAZY THINGS
                                                      years, he financed his physics studies
                                                      by mixing cocktails, spending his days         “The mere thought that we can under-
                                                      at the university and his nights at the        stand something that is so large and so
                                                      bar. Even today, he still gladly plays         complex as space is simply fascinating,”
                                                      bartender for his friends. No one has          says Khochfar. “It’s like an enigma, a
                                                      ever complained. “I still make the best        great mystery that I can unveil a bit
                                                      caipirinha east of Brazil,” he says and        here and there with my science.” It isn’t
                                                      laughs. “I am absolutely certain of that.”     quick. It takes effort. But Sadegh Khoch-
                                                      And this despite the fact that Khochfar,       far is persistent.
                                                      a lively Hessian with Iranian roots,               For as long as he can recall, he
                                                      drinks no alcohol himself. He says he          wanted to be an astrophysicist – a the-
                                                      simply never felt the need to try an al-       oretical astrophysicist, to be precise:
                                                      coholic drink – regardless of who mixed        “It simply gives one more freedom to
                                                      it, regardless of how good it is.              think, to dream up new, sometimes
Photo: Axel Griesch




                                                           Sadegh Khochfar is a theoretician,        also crazy, things, and to explore the
                                                      not only behind the bar, but also in his       consequences.”
                                                      professional life, at the Max Planck               Crazy is not a word that describes
                                                      Institute for Extraterrestrial Physics         Khochfar’s career path. He followed
                                                      in Garching. Since May 2008, he has            the classical, perhaps even stereotypi-


                                                                                                                    1 | 12 MaxPlanckResearch   57
PHYSICS & ASTRONOMY_Personal Portrait




cal astronomer career: His childhood         home town. Nevertheless, Khochfar          Wednesdays and Thursdays, Khoch-
bedroom was filled with stacks of per-       moved out of his family home. He           far tended bar from 6:00 p.m. until
tinent books about the Sun, moon and         wanted to stand on his own two feet,       2:00 a.m., and weekends until 6:00
stars. As a ten-year-old, he devoured        wanted to finance his studies himself.     a.m. No wonder he didn’t want to
Carl Sagan’s masterpiece Cosmos. Of          But that also meant that he needed a       spend his nights also gazing at stars.
course he had a telescope, and of            part-time job.                             Instead, he saw other stars: Silvester
course he took advanced math and                 While still in high school, Sadegh     Stallone, for example. He didn’t order
physics courses.                             Khochfar had already met an experi-        a caipirinha, though, but rather a bor-
                                             enced barkeeper who taught him how         ing Jackie-Coke.
A TEATOTALLER WORKING                        to mix cocktails. The two traveled
AS A BARKEEPER                               through Germany with a mobile bar
                                             and put on a show like Tom Cruise in
But Khochfar’s career path also always       the movie Cocktail. However, the time                      0.20

had an unusual twist, a small kink,          pressures involved in his studies forced
                                                                                                                 log (M*) = 7.27
something exotic: normally, astrono-         him to give this up.
                                                                                                        0.15
my-crazed youth spend their nights               Sadegh Khochfar, the non-drinker,
                                                                                                                                                               Photo: Axel Griesch, graphic: MPI for Extraterrestrial Physics

                                                                                                                       z = 6.84
gazing at the starry sky. Sadegh Khoch-      heard that the hip Frankfurt club Café                                    z = 7.15
                                                                                         SFR [MO/ yr]




far, in contrast, preferred to read books.   Cult was looking for a barman. He got                                     z = 7.47
                                                                                                                       z = 7.80
                                                                                                        0.10
                                                                                               •




“Sure, it was nice to look at the individ-   the job – despite his rather theoretical                                  z = 8.14

ual constellations with the telescope,       knowledge of the subject matter, or
but it didn’t give me the ultimate           perhaps precisely because of it: “Be-                      0.05
thrill,” he recalls. “I always first want-   cause I wasn’t drinking any alcohol, I
ed to know what I was seeing. And            was probably the only one behind the
above all, where it comes from, and          bar they could trust with the cash reg-                    0.00
why it looks like it does.”                  ister,” says Khochfar with a laugh. But                       0.2   0.3    0.4    0.5     0.6   0.7   0.8   0.9
                                                                                                                              t / 109 yr
    The son of an immigrant, Khochfar        the quality of his cocktails left noth-
would have preferred to study astro-         ing to be desired, either. “As a barman,     Growth: The diagram shows that the
physics straight away, but that isn’t        you have to look at the faces of your        star formation rate of a galaxy increases
possible in Germany. So he studied           customers to see whether they like           with time.
physics – of course – in Frankfurt, his      your drinks.”


58   MaxPlanckResearch 1 | 12
                      The universe in three dimensions: The model above shows the distribution of galaxies in a galaxy cluster. The most massive galaxies in
                      early times end, in all probability, in the center of such clusters. Before the scientists feed the data into their computers, they must incorporate
                      in their calculations as many formulas from the physics patchwork family as possible (left).




                      Nor did Sadegh Khochfar give up his                  these processes require much less gas                 way around understanding the funda-
                      job at the bar when, after completing                than was thought. “What is interesting                mental laws of physics, extracting the
                      his intermediate exams, he switched to               about this is that these findings have                core messages and correctly incorporat-
                      the University of Heidelberg. For three              since become confirmed and accepted,”                 ing all that in our astrophysical models,”
                      years, he commuted between the cit-                  says Sadegh Khochfar.                                 says the researcher.
                      ies on the Main and Neckar rivers. “To                   Advanced physics course, physics                      It’s almost like being a barkeeper.
                      be honest, it was hard, but despite ev-              degree, Ph.D. in astrophysics, head of an             He, too, must know the characteristic
                      erything, it was a good time,” says                  astrophysics group. It sounds straight-               properties of the ingredients in order to
                      Khochfar. He wrote his doctoral disser-              forward, even almost boring. Sadegh                   find the right composition and mix a
                      tation at – of course – the Max Planck               Khochfar shakes his head vehemently.                  tasty cocktail. “Basically, astrophysics
                      Institute for Astronomy in Heidelberg.               “Astrophysics is a patchwork family.                  is the biggest puzzle one can imagine,”
                      His working group dealt with elliptical              In order to understand what is happen-                says Sadegh Khochfar.
                      galaxies, the most massive stellar sys-              ing in the sky, we have to make exten-                    Of course he enjoyed doing puzzles
                      tems in the universe.                                sive use of physics.”                                 as a child, no doubt about it. Today,
                          Sadegh Khochfar wanted to do                                                                           however, the scientist tends toward
                      something cosmological, something re-                ASTROPHYSICS – THE BIGGEST                            chess – in its more athletic variant:
                      lating to the formation of galaxies, a               PUZZLE OF THEM ALL                                    Khochfar fences, his weapon a foil.
                      field with many unanswered questions.                                                                      “Fencing really is like chess. You have
                      In his theoretical work, the young                   If you want to fathom how and why                     to try to find your opponent’s weak-
                      physicist was able to show that ellipti-             galaxies form, you have to understand                 ness, and then outwit him at the crucial
                      cal galaxies are not created – as previ-             gravitation and the theory of relativity.             moment,” he says. Size, physique and
Photo: Axel Griesch




                      ously supposed – by the merger of two                But you also have to take radiative pro-              speed are secondary here; for Khochfar,
                      spiral galaxies. Instead, there are al-              cesses, turbulences and hydrodynamic                  fencing is more a battle of will. “If you
                      ready two ellipses involved in their                 equations into account. “It isn’t easy to             are clever enough, you can also beat
                      birth. In addition, it turns out that                be an expert in all fields, but there’s no            opponents who appear to be superior,”


                                                                                                                                                   1 | 12 MaxPlanckResearch   59
PHYSICS & ASTRONOMY_Personal Portrait




he says. “On the other hand, there is                Primarily, however, Sadegh Khochfar                   And sometimes it goes wrong. Then
no one you can blame for a loss. You                 began his time in Oxford with that                    Khochfar’s computer obtains different
have to take the responsibility. That’s              which even now still dominates his                    results than the telescopes of the ob-
good, I like that.”                                  day-to-day work: simulations. “Tradi-                 servers who sit a few doors down. Then
    Zorro and musketeer films are what               tional theoretical models always as-                  discussion, interpretation and the
first turned the young Frankfurt native              sume a simplified, ideal system. Other-               search for errors follow. “In such cases,
on to fencing. During his final high                 wise, it wouldn’t be possible to calculate            we have to understand what went
school exams, university studies and                 them,” he says. But the universe is far               wrong, make appropriate changes to
Ph.D., however, he no longer had time                more complex. If, like Sadegh Khoch-                  the simulation, and integrate the miss-
for this unusual hobby. Khochfar didn’t              far, we want to understand it in detail,              ing physics,” says Khochfar.
take it up again until, with his doctor-             we need numerical simulations.                            But doesn’t that pose the risk that
ate in hand, he moved to Oxford in                                                                         the models are simply tweaked until
2003. Over time, Heidelberg had be-                  BALANCING ACT                                         they yield the desired result – in other
come a bit too small for him; he didn’t              WITH COMPUTER MODELS                                  words, that they plow through the al-
want to go to the US, and there were no                                                                    gorithms with a saber rather than a
positions available in Cambridge. The                But numerical algorithms are, initially,              foil? Sadegh Khochfar shakes his head.
offer he received from the “Heidelberg               also just an approximation of reality.                “We can’t manipulate the simulations
without mountains,” as the astrophysi-               The theoreticians try to incorporate, in              at will, because we are always bound by
cist jokingly refers to Oxford, couldn’t             their simulations, as many formulas                   fundamental physical laws,” he says.
have come at a more opportune time.                  from the physics patchwork family as                  Energy and angular momentum must
    “It was a magical time,” he says.                possible, but eventually they fail due to             always be preserved, and the equations
Khochfar collaborated with Joe Silk, an              the resolution and the computing time                 of hydrodynamics also apply to gas
authority in the field of cosmology. He              required. For galaxies with many billions             flows in galaxies.
continued to research elliptical galax-              of young stars, it is impossible, for exam-               “Basically, here, too, it’s like with a
ies, penetrating into ever more distant              ple, to calculate, for each individual star,          puzzle,” says the scientist. You start
times. And he met his wife, who at the               the nuclear fusion processes that ulti-               with one piece and try to attach the sec-
time was doing her Ph.D. in political                mately lead to the ignition of the star.              ond piece to it. If it doesn’t fit, it can be




                                                                                                                                                            First Billion Years Project: S. Khochfar and C. Della Vecchia (MPE); visualization: K. Reuter & M. Rampp (MPG RZG)
science. The two now have an eight-                  Instead, the astrophysicists resort to sub-           made to fit with a bit of force. With the
month-old daughter, so his focus is no               grid recipes, as Sadegh Khochfar puts it:             third piece, it’s more difficult, and with
longer solely on the growth spurts of                they tell their models that the calculat-             the fourth, nearly impossible. Eventu-
baby galaxies, but also on the develop-              ed clumps of gas should eventually turn               ally, the whole thing is so bad that
ment of his own child.                               into a star. It’s a balancing act.                    nothing fits together anymore.


Cosmic birth: Sadegh Khochfar’s simulation shows how baby galaxies could have formed in the early universe (left). Such systems presumably form
elliptical galaxies in the course of 13 billion years, similar to M 87 (photo right), but with less mass. The researchers believe that many baby galaxies
merge with one another during their development, thus forming larger galaxies.




60   MaxPlanckResearch 1 | 12
                      Teamwork: Simulating the cosmos on the computer is complex and time consuming. For the latest project, it took two years just to develop
                      the algorithms, with 30 million megabytes of data having been collected. This makes it all the more important to continually discuss the results –
                      as Claudio Dalla Vecchia, Alessandra Beifiori, Sadegh Khochfar and Jan-Pieter Paardekooper (left to right) are doing here.



                      The astrophysicist opens his laptop and            13.7-billion-year-old universe that they            sults. “It was important to me to go to
                      proudly presents one of his group’s                can recognize objects that formed a bil-            an institute where I can offer comple-
                      most recent projects. It’s one of the              lion years after the Big Bang. But their            mentary expertise, even if it means
                      highest-resolution simulations of the              images are weak and show few details.               that I am sometimes the exotic one,”
                      early universe. It shows the emergence             The next generation of telescopes, in-              says Khochfar.
                      of the galaxies during the first billion           cluding the James Webb Space Obser-                     He even turned down an offer to
                      years of the universe. From cold, green-           vatory and the European Extremely                   take on a professorship in San Francisco
                      ish glowing clouds of gas and dust, the            Large Telescope, will change that. “We              at the time – in favor of northern Mun-
                      first stars form – hot yellow dots that            truly live in a fascinating time,” says Sa-         ich. “Garching is simply a fantastic
                      eventually explode, pushing gas away               degh Khochfar. “It doesn’t happen of-               place to do astrophysics,” he says. “This
                      and distributing heavy elements in                 ten that one has the opportunity to pre-            is where cutting-edge research happens.
                      their surroundings. New stars emerge,              dict things and then verify their                   Nowhere in Europe is the density of in-
                      and galaxies form and merge together.              existence a short time later.”                      stitutes and astronomers higher.” Near-
                          It’s a mammoth project: it took                                                                    ly 500 people work and conduct re-
                      nearly two years to develop and test the           A SENSE OF HOME                                     search at Khochfar’s institute alone – a
                      algorithms and, finally, run the simula-           AND BELONGING                                       large, but above all international com-
                      tion. The processors of various comput-                                                                munity. For him, the man with Iranian
                      ing centers toiled for more than three             That is precisely why Sadegh Khochfar               and German citizenship, that was also
                      million hours; billions of particles had           came to the Max Planck Institute for                an important argument. “To be honest,
                      to be taken into account, and 30 mil-              Extraterrestrial Physics. In principle,             it gives me a very good feeling, a sense
                      lion megabytes of data accrued. “We                he could just as well have moved a                  of home and belonging.”
                      will undoubtedly need another year to              hundred meters further to the Max                       It wasn’t always like that: In the ear-
                      evaluate everything and exploit every              Planck Institute for Astrophysics – a               ly 1970s, Khochfar’s parents left their
Photo: Axel Griesch




                      last detail,” says Sadegh Khochfar.                purely theoretical institute. But Khoch-            home in Iran and moved to Frankfurt.
                          The real test will take even longer:           far, who says that he is sometimes a bit            His father, a carpet weaver, earned a liv-
                      at present, the best telescopes can look           too enthusiastic, wanted to face reality,           ing repairing carpets, while his mother
                      just far enough into the past of the               the observers and their measurable re-              stayed at home. Two years later, little


                                                                                                                                               1 | 12 MaxPlanckResearch    61
PHYSICS & ASTRONOMY_Personal Portrait




                                                                                         A battle of will: Fencing, says Sadegh
                                                                                         Khochfar, is like chess. “You have to try to
                                                                                         find your opponent’s weakness, and then
                                                                                         outwit him at the crucial moment.”




                                                                                         just like his two siblings. His brother
                                                                                         became a doctor, his sister is close to
                                                                                         finishing her law degree – and that de-
                                                                                         spite the fact that their parents never
                                                                                         went to university. “In Iran, people
                                                                                         traditionally set great store by educa-
                                                                                         tion,” says Sadegh Khochfar, “so my
                                                                                         parents always made sure that we did
                                                                                         well in school and that we received a
                                                                                         good education.”
                                                                                              They never told their son what he
                                                                                         should study. On the contrary: When
                                                                                         ever more astronomy books began pil-
                                                                                         ing up in his room, when he expressed
                                                                                         his desire to have a telescope, when he
                                                                                         finally said, “I want to become a theo-
                                                                                         retical astrophysicist,” their question
                                                                                         was rather: “And what do you plan to
                                                                                         do with that?” But maybe his parents
                                                                                         were just thinking of an old Persian
                                                                                         saying: “Those who live only from day
                                                                                         to day become either poets or astron-
                                                                                         omers.” Sadegh Khochfar occasionally
                                                                                         still gets teased about this today – even
                                                                                         if it doesn’t fit him at all.




                                                                                           GLOSSARY
                                                                                           Elliptical galaxy
                                                                                           In principle, one distinguishes between
                                                                                           irregular, spiral-shaped and elliptical
                                                                                           galaxies. The latter are among the oldest
                                                                                           systems in space. The largest elliptical
                                                                                           galaxies have masses of several billion
                                                                                           solar masses.
                                                                                           Extremely Large Telescope
                                                                                           A project of the European Southern
Sadegh was born. “I always enjoyed        the university as they had gone in high          Observatory (ESO) for a new, next-gen-
growing up in Frankfurt, because it was   school. As a foreigner, I had a bit of trou-     eration optical telescope. Its main mirror
very multicultural there,” he says.       ble from time to time.”                          will have a diameter of 39.3 meters and
Among the ten or twelve kids who met          Once, after completing his practi-           consist of nearly 1,000 hexagonal mirror
                                                                                           elements. According to the present
on the playground, only two were Ger-     cal electronics course, the anonymous            plans, the construction of the Extremely
man. Also at his high school, the pro-    results lists showed that only one stu-          Large Telescope is expected to be com-
portion of students from immigrant        dent didn’t pass the associated test. An         pleted in 2018.
families was a good 50 percent.           assistant matter-of-factly approached            Black hole
    That changed abruptly when he         Khochfar and asked: “You didn’t make             A black hole possesses such a large
went to Johann Wolfgang Goethe Uni-       it, did you?” Of course he had passed.           gravitational pull that not even light
                                                                                           can escape from it. The region where
versity. “In the beginning, we were a     “I found this reaction a bit strange,”           the escape velocity is greater than the
handful of foreign students who, fun-     he says today.
                                                                                                                                         Photo: Axel Griesch




                                                                                           speed of light is called the event horizon.
nily enough, met right away and al-           In the end, though, the astrophys-           Supermassive black holes are found at
ways sat in the last row,” says Khoch-    icist-in-training didn’t let such things         the center of most galaxies and play
                                                                                           an important role in cosmic evolution.
far. He was the only one who stayed.      lead him astray. He simply enjoyed his
“Things didn’t go quite as smoothly at    studies too much. He saw it through,


62   MaxPlanckResearch 1 | 12

				
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