Giovanni Carraro in the VLT control room.

I guess that by today you all know about the catastrophic earthquake that struck Chile last Friday. My colleague, ESO astronomer Michael Dumke has already published a post about this.

I have been living in Chile for two years, working as a postdoctoral fellow in La Silla, and I have many colleagues and friends that live there. I just had a long phone call with my old friend and best man Giovanni Carraro, whom I know since the years of university in Padua. He is now in Cerro Paranal, observing at UT2. He tells me ESO observatories do not report any damage. They were out of phone/internet reach for some time, but now things are back to normal. At the time of the quake he was at the telescope, but he did not feel the ground shaking. The VLT control building is in fact very elastic. He became aware of the catastrophe only twelve hours later, fortunately. By that time, in fact, some of the connections were fixed and he could talk to his family in Santiago. The situation was chaotic, but none of ESO people was injured. No internet and normal phone connection, problems with drinkable water, chaos in the supermarkets to buy food and so on. With the airport closed and many roads seriously damaged, connections to Santiago are very difficult. Although the situation is still critical, I now feel a bit better. When I got the bad news I was in Italy, in my home village. We were struck by an earthquake in 1976, which caused about 1000 dead, 40 on my village. And that was only 6.3 Richter. I was only ten at that time, but I have a very vivid recollection of what happened. In a few seconds I could see all those apocalyptic scenes. Smoke and dust, screams, and most scaring of all, the continuous growls coming from the depths. And I was imagining the anxiety of my colleagues up on the mountain, 1200 km away from their families living in Santiago, with no news about their conditions and thereabouts. It must have been terrible…

All our thoughts now go to the Chilean population, especially the poor people in Concepcion and in the towns which have been devastated by the tsunami wave on the Chilean coast.

Willy Benz at ESO.

Every week, on Thursday afternoons, ESO hosts the Munich Joint Astronomy Colloquium. This is organized by all the astronomical institutes in the Munich area (there are quite a few). The idea is to invite leading scientists to give an overview on a specific field of astrophysics. Yesterday it was the turn of Willy Benz, professor at the University of Bern. Willy is an expert in numerical simulations. I remember the first time I met him, at a NATO school in Spain, back in 1995. At that time he was doing Smoothed Particle Hydrodynamics (SPH for short) simulations of supernova explosions. However, if you look at his publications, you will see that he has done lots of work in the planet formation field, where he has applied his hydrodynamical models to study the accretion of planetesimals, impacts, crater formation and stuff like that. And, in fact, the title of yesterday’s talk was “What have exoplanets told us about planet formation?”.

Willy Benz explaining the Neptune-Peak. In the plot you can see the broad Jupiter-Peak (which Willy is indicating), the Neptune-Peak (in the middle) and the Earth-like peak (to the left).

As expected, given the appealing subject, the auditorium was full. Willy has started giving an introduction on the planet formation basics, as we understand them now. He started off saying that for many, many years, before the discoveries of exo-planets, it was believed that big planets (Jupiter-like) do not form close to their central star. Joking, Willy said this was based on many, many years of observations and studies on one single case (our Solar system). As it often happens in science, the first exoplanet, which was discovered in 1995 by Michel Mayor and Didier Queloz using ESO telescopes, destroyed this castle of ideas in one single shot. “This is one of those cases” - said Willy - “where one observation is sufficient to blow up a theory“. Since then, more than 400 exo-planets have been found, and the vast majority of them populates what was believed to be a forbidden region. Part of this is certainly due to an observational bias, in the sense that with the current instrumentation it is easier to discover massive planets that move fast (i.e. are very close to the central star. This is why they are also called hot-Jupiters).

What Willy and his collaborators have done, is to produce with hydro simulations synthetic populations of planets, and compare them to observations. The experimental data we have for each single exo-planet does not tell us very much in itself. The real power comes from statistics: that is the place where theoretical models and observations can be compared. “The discovery of the whole population of exoplanets is essential to provide important constraints on planet formation models” - said Willy. Although the planet formation field is still driven by observations, theory is starting to make some quantitative predictions. “If you believe the models (which you probably shouldn’t) - joked Benz - “we expect to see the Neptun-Peak coming up and, in the future, the big peak of Earth-like planets“. In fact, their models predict that the number of planets having characteristics similar to our Neptune (10 AU distance from the central star and Neptune mass) should be rater large (there the name of Neptune-Peak). From the observational point of view, unveiling this kind of planets requires a very high precision. Now we can measure velocities up to about 1 meter per second accuracy, with instruments like HARPS. In the future, we will be able to go down to 10 cm per second. The new high resolution spectrograph ESPRESSO is designed exactly for that purpose. This will allow us to detect planets well below the 10 Earth masses limit, and give us the opportunity to see whether, indeed, Earth-like planets are rare or not.

What I liked in Willy’s talk, besides of course the underlying physical robustness of his science, is his way of presenting things, always cum grano salis and within a wide astrophysical context, not too detailed but also not too generic.

Great speaker, great talk, great science.

Science Day at ESO

The staff of the European Organization for Astronomical Research (ESO) includes people coming from very different fields. Given the fact that we design, build and operate telescopes and instruments, our teams are composed by a mixture of mechanical, optical, electronic and software engineers plus, of course, some astrophysicists. These have a double life within the organization, since they do functional work for the organization, but also their own research (up to 50% of their working time). The purpose of this is rather clear: if the organization wishes to keep scientifically linked to the community it is serving, than at least a fraction of its staff must be active in research. By construction, since ESO is not a university, there are no large scientific groups and most of us are part of large international collaborations. Also (and this is done on purpose), the scientific staff of ESO covers a wide spectrum of astrophysical fields, so that within the organization is rather rare to have two people working on the same subject.

Exactly because of this, it often happens than one does not exactly know what the guy sitting in the next office is doing in her/his science time. With the purpose of reducing this potential problem and to stimulate possible collaborations within the staff, the Office for Science at ESO organizes every year the so called Science Day, where everybody is given the opportunity of telling the others what she is doing. And this is what happened yesterday. The overall organization has been growing significantly during the last ten years, so that now what we call the ESO Faculty includes more than 80 scientists, ranging from PhD students to full astronomers. So, in order to fit more than 80 talks in about 8 hours, we were given 4+1 minutes for our presentations. The sessions were chaired by some of our post-doc Fellows.

It is always amazing to see how many different and interesting topics one can work on in astrophysics (I guess the same is true, though, for any other scientific discipline). We heard about the contribution of comets to the content of water on Earth, methane on Mars, very old stars in the Galaxy, stellar seismology, optical interferometry… you name them.

Besides giving old farts the chance to see what the youngsters are doing and where astrophysics is moving to, it was also a good opportunity for the young researchers to get familiar with presenting their work in front of a large audience. An exercise which might turn to be very useful for their future careers. Well done, lads.

The SW embankment of the castelliere in Galleriano (photo by F. Patat).

As I discovered in the initial phases of the study, the issue about the orientation of these sites had been already raised by other researchers. The first written reports (in the ’40s of last century) were mentioning that they all had the vertexes aligned along the cardinal axes. The same conclusion was reported also in several archaeological studies. But, most important of all, a more astronomically-oriented analysis had been published in 1986 by Aveni and Romano on the Journal for the History of Astronomy. Anthony Aveni is one of the most famous researchers in Archaeoastronomy and he has written many papers and books on this subject. This was more than sufficient to stimulate my curiosity, besides being a clear challenge. The first step was to establish a contact with archaeologist Dr Susi Corazza, who is working at the Laboratory of Protohistory at the University of Udine. She gave me several reports of archaeological digs carried out in these sites in the last ten years and she also invited me to visit an open excavation in Galleriano, one of the three well preserved sites.

Archaeological dig in Galleriano. Well visible is the cross section of the embankment.

There I was exposed to a completely new way of doing research. I could walk over the embankment, watch the stratigraphic sections, have samples of earth in my hands, smell the freshly excavated soil… a contact to objects which is forbidden to astrophysicists. And, most important of all, having to do with human artifacts. The excavation campaign, supervised by Susi, was conducted by undergraduates, PhD students and post-docs, under the hot sun of August. I must say I felt several times overwhelmed by emotions.

Two of the sites had been surveyed from the ground by the University using a classical ground-based total station, while for the third (Savalons) nothing was available. For this one I had a different idea. In fact, there is now the possibility of getting a 3D mapping of a site using an airborne laser device. This is typically used for civil purposes, like topography and the like, bit it has been used also for archaeology.

3D rendering of LIDAR elevation data for Savalons (Credit F. Patat).

The concept is very simple. A laser beam is sent down, reflected by the soil and received back by the device, which is capable of measuring the time it takes the signal to come back, with extremely high accuracy. If you then know precisely where your device is, you can then reconstruct the elevation profile of any 3D structure, with centimeter accuracy. Easy, uh? Well, yes, but it requires some expensive equipment and an helicopter. This is why I contacted HELICA, a local company, which is specialized in this kind of work. “We have never done this before” - said to me Diego Plos, Helica’s Director - “so we’ll give it a try and see what comes out of it”. And, yes, they did it. In a matter of a few seconds the LIDAR (that is the name of the device) has collected about a million points, spaced by about 30 cm. Amazing! A ground based survey of these structures takes many days, to collect a thousand points at most. Not only, but based on the properties of the reflected light, during the post-processing phase one can distinguish between ground and false-ground data (produced for instance by foliage). The data are so good that you can see the signs of cultivations in the fields.

Aerial view of Savalons (orthophoto - credit Helica).

But most interesting of all, the geometry of the site (approximately 180m on a side) appears very clearly. Clearly, the orientation analysis with digital, geo-referenced data is just a matter of computer skills and the smell of the archaeological digs is already far away.To complete the analysis (terrain slope, horizon) I also made use of the Shuttle Radar Topography Mission, which is essentially based on the same principle and it uses a radar instead of a laser. With this, for instance, I can check whether a site has been aligned along the direction of maximum slope, something which was typical in the Roman centuriation to favor the draining of rain water. Or I can try to see whether the orientation was done along the direction to some remarkable structure on the natural horizon, like a far, high mountain peak.

In fact, in archaeoastronomy is rather easy to be carried away and see alignments everywhere. This is actually a bit of a plague in this field, and the enthusiasm brought about by the findings in Stonehenge and the like has created a generation of improvised researchers, who have not exactly followed scientific criteria in their studies. Therefore, more than a grain of salt is necessary. And this actually makes the whole thing attractive for a scientist. The analysis is almost over and I am now convinced that there is no alignment to astronomically significant directions in these proto-historical sites. Even the orientation to cardinal points, suggested by early investigations (and reported more by tradition than by measurement), does not hold. At this point you might wonder whether the disproval of previously reported “facts” is really useful. Well, yes, it is. Here in archaeo-astronomy as well as in astrophysics or in any other science, for that matter.

The human skeleton found below the mound close to Savalons (credit University of Udine).

Meanwhile the archaeological digs have continued. Most remarkably, Susi and her collaborators have opened the mound close to Savalons, finding a human body deeply buried under it, which has now been dated around 1800 b.C. You can watch a movie about this finding here on YouTube.

If they’ll keep finding tombs like this (this is the 3rd one), we will be in the condition of starting an analysis about the orientation of proto-historical graves in the High Friulian Plain. This is another interesting topic connecting human life (well, actually human death) with astronomy. An example study can be found here.

In a subsequent post I will report a bit more in detail about the kind of analysis I have performed on the three sites.

This entry was posted on Friday, January 22nd, 2010 at 2:47 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site. Edit this entry.

Map of St. Martin (Artegna-Italy).

I like astronomy very much at the level that I can say mine is not a profession, is rather a passion. But there are gray areas here and there. One of them, maybe the most important, is the level of abstraction it brings about. Having to deal with very far things, far in space and time, with no possibility to touch them, adds to the generic frustration that any scientist, if you look deeply enough, has to deal with. In astronomy, the closest you can get to your “object” is working on Solar System bodies. In some cases, you can even hope to get some extra-terrestrial piece of matter in your hands, dissection it, run chemical and physical analysis. But this is rather the [extraordinary] exception than the rule. For extra-galactic guys, like me, no way. Well, yes, maybe when a close-by Galactic Supernova will go off then we will have the chance of receiving even particles. But that might be the last thing we do

More seriously, at some point in my life, just before leaving for Chile, I started feeling a strong need for reconnecting to reality, to the day-to-day world, to humanities. How a supernova guy would do that without abandoning his profession was not clear for quite a while.

Sunset at St. Martin (Artegna-Italy) ten days after Vernal Equinox.

But the quest brought me somewhere. I have quite strong roots deeply planted in my homeland. And in the months preceding my departure to Chile (at that time I had no clue about how long I would stay there), I started reading all the books about the history of my small village. The eldest thing we have there is an ancient church, dedicated to St. Martin. When the Longobards  entered the Italic soil, they established in that area their first Earldom and, having a long knight tradition, they devoted many a church to St. Martin, S. George and St. Michael, all coming from a military tradition or having something to do with horses and knights. In one of the books there was a mention about the fact that St. Martin, rising on top of a prominent hill, like many ancient buildings, was oriented along the east-west axis. That was the start of it, because my attitude to measure things immediately generated the question about the accuracy of such an alignment.

Measuring the natural horizon at St. Agnes - Gemona del Friuli.

So, using rather simple methods, I measured the azimuth of the church’s axis, finding that it deviated  only 0.7 degrees from the geodetic E-W line. At that time I had not so much money, I was just out of my PhD and we had a 3 months baby. Chile was appearing close to the horizon and so I postponed any further study in that direction. But for the two following years I nursed this idea and I started a self-training in this discipline, which was indeed bringing me back to man through astronomy. I had finally found a way to reconnect to reality without giving up or betraying my “credo”. When, two years after, I got a position here at ESO-Garching (Germany), those places were much closer. I had some more money and I could afford buying a second hand Zeiss theodolite and a GPS receiver (at that time not so diffused as they are today). Equipped with this, a background in spherical astronomy, some home made software and lots of good will I started getting acquainted with the required techniques. I first started with ancient churches in Friuli, some of which were originally built around the V-VI century a.C., all erected on high hill tops. And something interesting indeed came out of it, bringing about a new kind of emotions, which my main research field could not have given me, by construction.

Castelliere (artist's impression).

Encouraged by the results I then moved one step further, and I started an orientation study on three proto-historical sites (about 1800-1500 b.C.) in the High Friulian Plain, in collaboration with the Laboratory of Proto-History of the University of Udine. These are large (150-200 m on a side) earthworks, usually called castellieri, with embankments that can reach 5 meters in elevation above the surrounding plane, and base widths reaching 20 meters. Imposing manufacts, indeed. If you know where they are you can easily see them in GoogleEarth (see the pictures below). Their purpose is not really clear, but the archaeologists think they were used as fortified villages. Although in the High Friulian Plain there are remnants of many such sites, only three are rather well preserved. The others have been leveled mostly  during the intensive agricultural activities that took place last century. These three sites have a roughly quadrangular form, in contrast to other similar structure seen for instance in Istria, which had a circular shape. This of course offers the possibility of running an orientation analysis. I will tell more about this in the next post.

The castelliere of Savalons (GoogleEarth).

The castelliere of Galleriano (GoogleEarth).

This has nothing to do with Astronomy (or maybe it does, but this it is not so important). I am just back from the Prinzregenten Theater in Munich, where David Fray gave a very impressive concert, playing Schubert and Bach. What amazes me is how actual and vivid Bach can sound in the hands of Fray. All that geometry transfigured into passion… Have a look to this and you’ll tell me. Certainly the guy is eccentric (and a beautiful man, ladies tell me), but when he plays Bach he brings about something I had never heard before. Bach and Astronomy are so strictly related in my own experience that I could not resist to share this with others.

Good night.

Like everyday, this morning I brought my little son to the kinder-garden. On the way I met Tim de Zeeuw, the Director General of ESO. From the window of my office I can see his and I had noticed he had been away for quite some time. I took advantage of this for briefly chatting with him about how jet-lag is annoying and so on. “Yes” - he said - “but sometimes interesting things happen”. I was kind of guessing that something exceptional was coming and the conversation was going to turn into something much less trivial than jet-lag…

Michelle Bachelet, President of Chile

And, in fact… “While visiting our sites in Chile, I was sitting in my office in Santiago and, at some point, I got a phone call”, he started off. “The President of Chile was on the other side of the line”. From this point I can only imagine how things went and what follows is a fiction like dialog (but I guess things were not very much different from this).

-”You are planning to build a very large telescope, right?

-”Yes, Madame President, that is true”.

-”Have you already decided where you will put it?”

-”We are in the process, Madame President”.

-”Would you consider placing it in our Country?”

-”Yes, Madame President, we are certainly considering that”.

-”I am glad to hear that, prof. de Zeeuw. What can we do to help you?”

Of course this is only my guess on how things went, Tim did not reveal the real nature of the meeting. But in sight of the big enterprise ESO is going to start soon (that is the building of the largest optical/near-IR telescope on the planet, the E-ELT), I would not be surprised the topic of the discussion was quite an interesting one.

Although I am not in the least involved in these political things and the future of the E-ELT does not depend on my skills and wills, it is quite exciting to be very close to where things happen.

You can find some more details in this ESO press release.

I am now sitting in the meeting room in an hotel, together with other people from my Division. The topic of this 3 days retreat is the revision of the current end-to-end data flow system of the VLT, in sight of the E-ELT era. Yes, because contrary to what I had naively thought when I started my career in astronomy, operating a [big]  telescope is not only matter of screws, optics, electronics. It also means scheduling, data archival and distribution, astronomers training, operational plans and so on. And all of this makes into the success of this kind of facilities.

Tomorrow I will jump back to science. The plan is to finish up a paper for the Journal of Archaeastronomy, edited by the University of Texas. In my next post I will talk about this.

While reading Rare Earths by Peter Ward, I found the following quotation:

“Much of the work we do as scientists involves filling in the details about matters that are basically understood already, applying standard techniques to new specific cases. But occasionally there is a question that offers an opportunity for a really major discovery.”

W. Alvarez, “T. Rex and the crater of Doom“, 1997, Princeton, NJ, Princeton University Press

If you are a scientist you will certainly recognize yourself in there. All your professional life is about this quest. And what (but only sometimes) makes you sad is that you are aware this major discovery will never come. Times have changed and those mythical ages when isolated scientists were making exceptional discoveries are now probably over. But still, in the back of your head, there is a small flame, always burning. It is the hope, against all facts, that someday something great will come. If it won’t, well, I tell you it is worth the effort anyway

The relics of the Roman Forum in Zuglio (Julium Carnicum)

It is almost time to leave for Xmas vacations. Finishing up a few things  and getting ready to leave to Italy. There are many aspects that make these holidays appealing. Among those, is an archaeological exploration foreseen for the first sunny day between X-mas and new year’s eve. This story begins a couple of years ago, when I studied the orientation of the ancient church of St. Peter above Zuglio (the Roman town Julium Carnicum). While reading the related literature I realized that, at the times of Romans, this and other similar sites (all on mountain tops), were used as sight stations, to visually communicate the arrival of possible invaders (by means of smoke in daytime and fire during the night) to the large town of Aquileia. This town had been founded in 181 b.C. to prevent the invasions by barbaric tribes from the NE of the Italic peninsula (ad Illyricos objecta montes), which has a rather easy to cross border. One of the possible ways to trespass the Roman limes was a narrow pass, today known as Plockenpass. But from there all the way to Aquileia (about 80 km to the south, on the Adriatic sea) the landscape is full of mountains and it requires a number of intermediate stations before one finally reaches the Friulian plain.

Horizon azimuthal map for Cesclans (credit F. Patat)

My curiosity was captured by the fact that while it was clear how the visual signals would get along the valley from Plockenpass down to what today is called Cesclans (known archaeological site on a high, easily defensible top), much less clear was how those signals could get to the plain. In fact, a chain of mountains prevents the sight of the Friulian plain from Cesclans. Clearly, a further station was required. I took a note and let the thing rest for quite some time. But at some point, I realized that I could use the SRTM survey data for my archaeoastronomical studies. While doing this I also thought that they might be of some help to solving the problem of the missing station remotely, even before thinking about an on site expedition (it is about 500 km from here, just across the Austrian/Italian Alps). The idea is simple. You write a program that, using the digital elevation data provided by the Shuttle Mission (and free for download), determines the distance of the horizon in all directions seen from a given site (taking into account Earth’s curvature and atmospheric refraction). I had originally done this to produce synthetic horizon profiles for the analysis of some proto-historical sites in the Friulian Plane. But the application to the case of Cesclans was straightforward. You can see the result in the graph here to to right. The red dot marks the position of Cesclans. As you can see, there are several windows that open the sighting to NE and NW (the rightmost is the one which connects to the Plockenpass valley), while to the south the horizon is closed. With one, narrow exception (marked with the red circle).

Mount Faet at dawn (Venus is rising to the left).

If you go to a map, you will see that this coincides with a 750m mountain in the pre-Alps. This is Mount Faet, by coincidence (!) just above my small town of Artegna. Immediately after finding this result I wrote to a friend of mine that lives in the area, asking him to verify whether this window was real and not just an artifact of my calculations. The day after I received a digital picture taken with a tele-lens from Cesclans in the appropriate direction. And, indeed, a tiny portion of mount Faet was visible (if you knew it was there).

The next step was to go on site, with the aid of a GPS, to see whether in the relevant area (my calculations were giving a spot with a diameter of roughly a km, at an altitude between 550 and 600m above sea level) there was any trace of human artifacts that could indicate the possible presence of statio. Nice plan for summer vacations.

The stone paved path that leads to the top of Faet.

So, at the end of August, with my young assistant Riccardo, I left my place and started hiking along an ancient path that leaves from the base of the mountain. Interestingly, there is a network of stone paved paths that lead to the mountain top, which have been attributed by archaeologists to post-roman epochs. According to them, the mountain was used a refuge during the barbaric invasions that followed the fall of the Roman Empire. We started off very early, in the fresh air of dawn break. The GPS was telling me that it would take about one hour to reach the site, although the straight line distance from the starting point (placed at about 300m above sea level) was less than two km. I knew that path, since I had been there many time during my childhood to collect chestnuts. But I had never paid so much attention to the way the path was paved. Indeed, it is kilometers of stones. At times, in between the threes, we could see flat embankments surrounded by stone walls, probable relics of those ancient refuges identified by the archaeologists. From time to time, we get a glance of the Friulian plane that extends to the south. At some point, a message appears on the GPS, telling us that we are within 50 meters from the targeted position.

Cesclans seen from mt. Faet.

By coincidence, there is a clearing in the wood produced by a track recently built to facilitate the access to the mountain (to prevent fires and so on). From there, we can finally look into the direction of Cesclans. And indeed, there it is. We can see the mighty tower of Cesclans’ church with naked eye in the light of the rising sun, just above the low mountain. You can easily see it if you click on the photo here to the right.

This is the definite proof that there is a sight-line between the two sites. Notably, from mt. Faet you can see down the whole Friulian Plain and, in clear days, you can even see the sea. Obviously, Aquileia is still far, but the Plain has several hills that could be easily used as intermediate stations. So, this is not much of a problem. However, having a viable sight-line is one thing. Being certain it was used by Romans as part of their defensive signaling system is a different issue, which can only be demonstrated by archaeological findings.

Relics of stone walls on mt. Faet (about 580m a.s.l.).

For the time being this remains an interesting possibility, supported by visible, ancient human manufacts. That day, Riccardo and I adventured a bit in the bushes and found several traces of stone walls close to the sighting site. At home, then, I had a look into a book describing an archaeological surfaces survey carried out in the early eighties in this part of mt. Faet. Indeed, these manufacts were classified as defensive structures dating back to the Longobard period, possibly built on Roman relics. All of this makes the thing even more appealing. In the same publication I also found the description of a number of proto-historical mounds, not far from the site Riccardo and I visited last August. That is the target of the visit planned for the X-mas holidays. This has now brought me rather far from astronomy (from which I started), but it is extremely stimulating and helps me getting back from void spaces into humanities. Although far into the past…

Bob Kirshner (right) and Brian Schmidt (left)

When I was close to the end of my Master in Astronomy at the University of Padua, I do not exactly remember why I decided to do my thesis work on Supernovae, under the supervision of prof. Roberto Barbon. So, sometime in early 1991 I got a date with him and his collaborators to discuss a possible project. At the end of the meeting, one of his two assistants (the inseparable duo Turatto&Cappellaro/Cappellaro&Turatto) gave me four reviews and told me: “Here is all what you need to know about Supernovae“. On the train that brought me back home, I started having a look. It was in fact papers by Robert Kirshner, David Branch, Alex Filippenko and Craig Wheeler, whom I immediately considered as the bosses in the supernova field (and I still do). As seen in retrospective they clearly doomed my fate. Many years have passed, but time does not seem to have had any effect on them. However, they (as we all do) are getting of age.

Bruno Leibundgut and Nikolaj Chugai

There is a tradition in the astronomical community: whenever one of the VIPs turns sixty an international conference is organized in her/his honor. Last August it was the turn of Robert (Bob) Kirshner, who was celebrated at the Stellar Death Conference at the Kavli Institute for Theoretical Physics in Santa Barbara (CA). Conferences are ideal to exchange ideas, to see what others are doing, to say things that you would not write in a paper, to brain-storm an so on. But are also great occasions to touch the more human aspect of science, to better know our collaborators (and competitors), to meet brilliant people on grounds which are all but scientific. And this conference was particularly good under all aspects. Basically all people working in the SN field (both theoreticians and observers) were there. More than 150 researchers from all over the world. The conference, which was very well organized, was very fruitful and has clearly shown how active the supernova field is.

Sunset in Santa Barbara (CA).

As the title of the conference tells you, the topic was the [explosive] endings of stars. And the zoo is getting indeed full of weird beasts. The new searches looking for transient phenomena have already started finding new kinds of explosive events. And more will come in the next years, as the projects get up to speed. These surveys are run with robotic telescopes equipped with wide field of view cameras, able to scan the whole sky in a week or less. They start exploring a time domain that so far was not accessible, and produce huge amounts of digital data at an astounding rate. And, of course, whenever new objects are discovered, new problems and questions come up. This is why astronomy, and science in general, will always have something to work on. Amazing. When Fritz Zwicky started working on Supernovae (actually, he and Walter Baade named them), he had troubles in convincing people that this was worth doing.

Adam Riess is perplexed about "lambda" (left) but he feels much more comfortable with "w" (right). Ask a cosmologist if you wish to appreciate the humor;-)

It was actually Roberto Barbon (who spent some time at Caltech under the supervision of Fritz Zwicky) to tell me that story. Zwicky had started his own supernova search, but it was very hard for him to get funded, essentially because who was distributing the grants did not see the purpose of such an effort. And today we discover about one new SN per day. This number is doomed to grow to thousands per year as soon as the large automatic surveys will be deployed.

The study of supernova explosion is important for a number of reasons. The first, most intuitive one, is that this is really the only way to see the interiors of a star. Normal stars (like our sun), spend their lives in a quiet way, and the only thing we can observe is the radiation they emit (in the case of the sun we also get some particles, the solar wind). And from this we have to deduce how things work in its inner parts. But in the case of a supernova explosion, the star is taken apart. In this process the “normal nuclear burning is altered and so we do not exactly see how the star looked like during its previous life, but still we see how it looks inside.

Alex Filippenko, Kenichi Nomoto and his wife

That is one thing. But then, you can imagine that the ejected material, which travels at speeds exceeding 10,000 km/hour, must have some impact on the surrounding regions. And that is indeed true. It is believed that supernovae are the major contributors to the kinetic energy of the interstellar medium. And so what? Well, the fact is that this energy input is fundamental, for instance, to trigger episodes of star formation. So, dying stars provoke the birth of new stars.

Finally, normal stars synthesize heavy elements (iron, calcium, oxygen, …) in their interiors through the nuclear fusion. However, these elements are doomed to remain buried there forever. Some stars actually lose material from their surface (for instance, planetary nebulae), but a supernova ejects into space large amounts of matter in very short amounts of time. And this has a major effect on the chemical evolution of galaxies. That gas, which is initially dispersed into the interstellar medium, one day would form a cloud, which will collapse and give birth to new stars with a modified chemical composition (or more metal rich, as astrophysicists would tell you).

There are many more reasons why studying supernovae is very important in a general astrophysical context, and all of them had a part in the Stellar Death conference. If you are interested have a look here, were you can also find the online talks. In particular, if you wish to see my presentation, here it is.

Bob Kirshner during the party in his honor (artist's impression)

Of course, in this kind of conferences there is always lots of young people, PhD students and post-docs, who make the whole thing very lively. And it is actually they who bring a very cheerful atmosphere, which makes evenings very relaxing and entertaining (especially after hours of listening to complex presentations on neutron fingers ;-). I probably do not belong to the young generation anymore, but I kind of pretended it and mixed with them, together with my wife Adele, who always enjoys very much the atmosphere one breaths in these occasions. I think that the night immersions in that beautiful, steaming jacuzzi at the hotel (in hours when it was officially closed) will remain in the memories of many of us

The conference was the best one I have ever attended, for all aspects (the fact that Adele and I were alone, with no kids, like in second a honey moon, is not to be underestimated ;-). I have seen old friends that I had not met for a long time. Like Nikolaj Chugai, head of the Dept. of Astronomy in Moscow, to whom I owe so much. Or Craig Wheeler, whose fascinating personality never stops to surprise me. I will visit him in Texas next year and I already feel excited about it, because he has the power of arising my enthusiasm.

We are all thankful to Bob Kirshner and we wish him to turn sixty again… next year!

Happy birthday, Bob!