The story of the R-Stern

The streets of Granada. In May 2011 I went to a conference called “Stellar Clusters and Associations” in Granada. I presented results from our SONYC project, a long series of observations and papers aimed to find the lowest mass things that can form like a star — brown dwarfs and free-floating planets. In the afternoons I walked the streets of Granada. Sometimes alone, sometimes with Dawn, a friend and colleague from Boston. It could have been my last conference, grant proposals fell through, job applications I never heard from again. For Dawn it actually was the last conference. At this pre-apocalyptic stage in both of our careers, I decided to tell her the most ridiculous story of my life as an astronomer. For the first time I told another astronomer the biggest secret of my career. The story of R. As story that cannot be told in a scientific paper.

Part 1: The dissertation dilemma

It was a weird conference. The days before the meeting I was sitting on a Karst mountain in Andalusia in the Sun and read CS Lewis. Three days, completely alone. One morning the police came and searched my rental car for drugs. That was my only interaction with humans. Dawn and I went to the Alhambra, just an hour after all the other people from the conference, in the evening twilight. We tried not to catch up with the group of astronomers. It was not easy, they were just so slow. I sat for a long time on a throne and watched a bat flying circles under the roof. By and large I tried not to be an astronomer, the whole week.

Almost ten years earlier. Hundred kilometers to the east of Granada is Calar Alto, a mountain crowned with the three white domes of the German Spanish Astronomical Centre. Calar Alto is neither beautiful or majestic. The summit is surrounded by spruce plantations with messy clearings running down the mountain in all directions. The soil between the trees is grey and rough. At lower altitudes the mountain is a desert, or, more precisely a semi-desert, the only region with semi-arid climate in Europe. Humidity kills light. Particularly red light. The water in the atmosphere eats up photons. In that sense it resembles the equipment astronomers use to capture light. Humidity is the natural enemy of astronomers. Calar Alto is an ugly bastion of astronomy.

I spent so much time on this ugly mountain. Waiting for clear skies. Playing pool billard, against myself at four o’clock in the morning. Juggling. Eating fish soup. Climbing rocks. Random walks around the hills. I found deserted huts where dead animals hung from the ceiling. I was a postgraduate student in astronomy and time didn’t matter. A telescope on a mountain beyond civilisation was all I ever wanted. Okay, that’s not quite right, I also wanted sex and a new car and I wanted this bloody melancholy to stop and the inferiority complex and the song on the radio, but a telescope on a mountain was a good start.

In October 2002 it is my job to monitor the Pleiades for full three weeks, for the big Pleiades chapter in my PhD thesis. The Pleiades are a cluster of stars, all born hundred million years ago, about four hundred forty lightyears away. For the unaided eye, the Pleiades are six or seven or eight stars, densely packed together. If you can see more, you have good eyes. A big telescope sees a thousand stars in this cluster. I want to measure their rotation periods. The idea is simple. Stars are covered with dark spots, like the Sun, like an apple that has spend too much time lying on one side. As the spotted star rotates, its brightness changes periodically. You just measure the brightness of stars over and over again, and if you see a period in these measurements, you are done. I measured a few periods for tiny stars in the Pleiades. They are published in my second paper, which appeared in summer 2004. It was a solid job. The stars keep turning.

What I primarily remember from this run is that I couldn’t sleep anymore after 12 of 21 nights at the telescope. My body didn’t want to sleep anymore. The sun is rising, forget sleep, that’s what my body said. But, but, I argued. It didn’t help that a group of feral goats banged against the walls of my darkened bungalow bedroom the entire morning. They also had bells tied around their necks. My sleep deficit grew. By the 15th night, I was officially a zombie. While the telescope was gathering light, I fell asleep. Three minutes sleep, alarm clock, telescope adjustment, again sleep. But then I had a great idea. I cheated my body. I pretended to go to bed after dinner, brushing my teeth, reading a good-night-story, all that. I slept, but only for an hour. Then I woke up and went to the telescope. My body bought the trick. The final five nights were fantastic. In the firm belief that I would never return to this mountain, I played Brahms’ Requiem from my dome, very loud, very obnoxious.

One of the stars in my Pleiades field did not follow the script. The star is not even a star, it is a brown dwarf, an object with a mass too low to sustain stable fusion of Hydrogen to Helium, the source of energy that fuels stars like the Sun for billions of years. My brown dwarf, which will only be called “R” in the following, has only about 5% the mass of the Sun. R produces only 1/1000th of the light the Sun emits. As it ages, it will get dimmer and dimmer. R will literally disappear in front of our telescopes. This will happen over timescales of billions of years, impossible to witness. But in October 2002 I observed a different kind of dimming. This thing, the mysterious brown dwarf R, faded within half an hour, while I was watching. For a few minutes it appeared to be only half as bright as usual. Then it recovered quickly to its normal state. I have witnessed a short, deep, and magnificent eclipse. Even better: I saw it with two telescopes at the same time.

I couldn’t believe it. I mean, disbelief is not unusual for me, there are days when I cannot believe in the existence of my own hand. But this wasn’t just a moment of disbelief, it took weeks to overcome. Between the brown dwarf and me are a detector, a telescope, a few hundred kilometers of air, not to mention four hundred fourty lightyears of empty space. Many things can happen in that space. I re-do the entire data analysis, over and over again, in different ways. The eclipse doesn’t disappear. I check everything again. Still. It’s such a dramatic effect that I don’t really have to measure anything, I can see in the images how the star disappears. But what really killed my doubts is the fact that I have detected the eclipse with two telescopes at the same time. Without the second telescope, who knows.

There are a number of ways to reduce the brightness of a light emitting object by half. You could eclipse half of it with something that does not emit any light. Like holding your hand in front of half of the lamp. Or you could have two objects equal in size and brightness, and one of them moves in front of the other. The second scenario is easy to imagine for R. All brown dwarfs of the same age are about the same size. If R is in fact two brown dwarfs of equal brightness, the eclipse could simply be one of them eclipsing the other — an eclipsing brown dwarf binary. The first scenario is more appealing. A dark compact body able to eclipse half a brown dwarf in such manner can only be a planet. A planet orbiting a brown dwarf, something that was never seen before.

Secretly I always hope for the big discovery. There are probably people who are totally okay with publishing negative results or long lists of numbers for their entire scientific career. I admire these people. Negative results are results, too, they say. And they are absolutely right. But secretly I still hope for the big discovery. Whenever I show people our telescope, they ask me what I have discovered lately. I want to have an answer to that question, a real answer, not ‘negative results are results, too’. The longer I work in astronomy, the more people around me discover things. But not me. I measure, I derive, I confirm, I refine, I improve. I’m a master of incremental progress. But I don’t discover anything. At one point I helped discover a globular cluster, hundred thousand stars at once. But that’s nothing. Hundred thousand stars, only some bloggers in Russia are interested in that.

Either way, this discovery could be monumental. Maybe not for humanity, but definitely for astronomers. Eclipsing systems are key to everything we know about stars, brown dwarfs and planets. The shape of eclipses depends on the size of the eclipsing bodies, it is one of the very few ways to indirectly find out what a star is. Or a brown dwarf. Or a planet. If something is eclipsing something else for an observer on Earth, this observer gets very excited. Astronomy is all about indirect inferences, because the targets are usually too far away to see anything directly. By pure geometrical coincidence, these eclipsing system become famous, at least among astronomers, because they give us unique insights. The discovery paper for the first and so far only known eclipsing binary brown dwarf was cited a few hundred times, more than any of my papers. The discovery of the first planet eclipsing its host star received more than thousand. Careers are built on eclipsing systems.

My third paper, the one with the periods in the Pleiades, appears in July 2004, a few days after I submitted my dissertation. I walk straight from the university to the employment agency and register as unemployed. My savings are dwindling. The career advisor at the office is pretty much clueless when it comes to the job market for astronomers in a rural area in Germany. Soon after that I got the offer for a postdoctoral position — but it’s in Toronto, not Thuringia, a pretty big difference. It was an eventful summer. I also broke up with my girlfriend and moved back into my old room at the observatory. That was just a couple of days before the Venus transit on June 8th 2004. A dark planet obscures a shining object, maybe exactly what happens to our R-object. I’m staring at the dark spot on the Sun, mostly confused. The foxes are screaming at night. The wild boars are turning the forest upside down. The R-star is not mentioned in my dissertation, not a single word. I had other things on my mind.

We began to search for independent confirmation. “We” in this case were my supervisor and I. Nobody else knew about it. It was the best kept secret of my life. Directly behind my office in Tautenburg forest in Germany was the beautiful, white 2-m telescope, the largest Schmidt camera in the world. In October 2001, one year before that observing run on Calar Alto, we had already observed the same stars with our own telescope. It wasn’t a good campaign, lots of rain, lots of clouds, and lots of bad data. But we are not looking for something subtle. We are looking for a monster. By sheer luck I find something in this crappy dataset which might be an eclipse, three hundred sixty three days, almost a year, before the Calar Alto event. I add this number to the date of the Calar Alto eclipse and predict future events. None of them could be observed. Either the presumed eclipse happened during daytime or the weather didn’t cooperate. We observed the hell out of this field, in 2003, 2004 and so on. I didn’t see anything. By now my so-called predictions were too inaccurate to be useful. We kept observing.

At this point I was still a PhD student, without a clear future, without a clue, without a publication record. I was anxious. My supervisor was the only person on Earth who knew what I could do, who could vouch for me. I thought about publishing the R-eclipse right there, as it was, unconfirmed and all. Look, we have seen this thing, we have no idea what it is, but there you have it. That would have been the story, so I imagined. I was told that you don’t publish half the truth, an unfinished story, without knowing anything. You don’t publish unsolved problems. Maybe that’s true, but I didn’t get it. I couldn’t possibly publish it alone. There was just no way. This was also the time when I started listening to Mars Volta, obsessively, night and day.

Part 2: The postdoctoral playground

“This apparatus must be unearthed.” There is only one definite way to find out what R really is, an eclipsing brown dwarf, a planet, or whatever. You have to weigh the eclipsing body. The standard method of doing that is well known. It relies on the fact that, in a system with two bodies orbiting each other, the orbits are determined by the masses of the bodies. The idea is to measure the velocity of the object that you can see over time. You expect to see a wobble, a periodic oscillation of the velocity, as it revolves around the common center of mass of the system. The Sun wobbles because it is moved back and forth by its planets. The Earth wobbles because the Moon is pulling it back and forth. The R-star should wobble as well. Depending on the mass of the companion, the amplitude of the wobble would be meters per second or kilometers per second.

The academic career starts with a loss of control. Just when you are beginning to stand on your own feet, you tie yourself to an academic father figure, the supervisor, who has to teach you to walk into the unknown. The PhD is just the proof that you are now able to walk on your own. After that you enter the postdoc life, a limbo state between academic childhood and adulthood, a second academic puberty. You leave the father figure. You change jobs every two, three years. You change jobs, supervisors, universities, countries, continents, alliances, collaborations. You collect friends and colleagues all around the world. Work and private life happen mostly in your laptop and over the internet. You work as a nomad in international networks, continuously hunting for the next paper and the next job. These are the best years in the life of a researcher.

Measuring the wobble needs spectroscopy with very high resolution with a very large telescope. We let a certain person in on the secret, a colleague specialised on this technique, and apply for observing time. In 2004 we get the time at one of ESO’s Very Large Telescopes, a gigantic thing with a mirror the size of a badminton court. We get the spectra, but they are very difficult to analyse. R, our mystery object, is just very faint. It is not easy to measure the velocity of something like that. Nobody has done it before. There is not much in these spectra, mostly just noise. Our colleague, the expert, changes jobs and occupations. The spectra remain unanalysed. One year later, in 2005, they become publicly available. Everybody can look at them now. But without the eclipses they are useless. Only we have the key to this system. Or, rather, we don’t.

In the early years it was exciting to think about R. Since 2004 it was mostly embarrassing. But not always. Sometimes it felt good, in a perverse way. The idea of research is to see something new, something that nobody else has seen before. And then to tell the world about it. I break the rules and keep the secret. It is an absurd secret, a thing that is almost impossible to find, not as obvious as the Galilean moons or Saturns rings or the supernova in the Magellanic clouds. When we played hide and seek as kids, my goal was always to find a perfect hiding place. A hiding place that was impossible to find, where I can hide infinitely long. I sit in a secret hole in the hedge. All the other kids circle around me and try to find me. I can see them, but they cannot see me. I know where I am, I have privileged information. Nobody else can touch me. That’s exactly how this knowledge about R felt. The brown dwarf is the infantile Aleks, sitting in a hedge, feeling power, for the first time in his life. Power through secret knowledge.

From 2004 onwards I spent a lot of time on conferences about brown dwarfs. Over these years we make tremendous progress in our quest to explore brown dwarfs. But one issue remains. At every single conference, in La Palma, in Hawaii, in Los Angeles, in Munich, in London, in Fuerteventura, every year, the same problem comes up. We cannot say for certain how big brown dwarfs are. We do not know exactly how mass and size and brightness and age relate to each other. The fundamentals are shaky. We work with uncalibrated models. If we just had an eclipsing brown dwarf, people say. Year after year. I sit in the audience at these conferences and know something. I remain silent. Until Granada 2011. It took almost ten years for me to tell the entire story to another astronomer. Just one, of course. Under the pledge of secrecy. In the streets of Granada.

Why did I keep the secret, after all these years? Ten years after the discovery? I was a postdoc, I didn’t depend on my doctoral father anymore, I can do whatever I want. I could. I should. But there are two problems, both completely unscientific. The first problem: To publish anything, I first needed the data. The images are on magnetic tapes, somewhere, in Germany, either in Tautenburg or in a cupboard near Fulda, where my parents live. I, on the other hand, lived in Canada, Scotland, Ireland. The second problem: Getting the data, analysing it, and then publishing it would have taken weeks and months. Time that I used to write other papers, easier papers, less complicated, and less uncertain. I was successful, after all, with all my other projects. The R star more and more seemed like a waste of time.

Among other things I became increasingly interested in the question if brown dwarfs can form their own planets. In 2006 and 2007 I published three solid papers on disks around brown dwarfs, the presumed birth places of their planetary systems. In 2012 I am on a team that uses the new ALMA interferometer to take images of a brown dwarf disk. We showed for the first time that some brown dwarf disks have enough mass to form planets. We learned that brown dwarf pairs are rare, one of the reasons why finding an eclipsing one is so tricky. We also showed that grain growth occurs in these disks, the initial stages in the formation of rocky planets. So, planets around brown dwarfs may exist, but most of them will be small and crappy, that’s what we have learned. If R really is a brown dwarf binary, or if it has a big planet, it must be a rarity. Over these years I learned a lot about R’s secret companion, about its possible origin, its rareness, it’s physical conditions, without even looking at him. I circled around it.

There is another problem: The longer we wait, the harder it becomes to publish this unfinished story. Hey, look, ten years ago we have seen this event, but we kind of didn’t want to say anything, so. How are you going to explain THAT? How are you going to explain that you found something important, ten years ago, but didn’t tell anyone? Just because? Ridiculous. You just can’t do it. The longer it takes, the more years pass, the more impossible it becomes to publish anything. The R star withdraws from astronomy. I seriously consider publishing the whole thing as a novel, as fiction. If nobody else rediscovers R, nobody will ever find out. I will take this secret into my grave. Every year I talk on the phone with my former supervisor, usually late in summer, when the Pleiades appear again at the evening sky. Every year we plan new observations. We continued to observe the hell out of this object. Over the years, these observations turned from science to nostalgia, a thread that connects my uncertain and exciting postdoctoral existence with my insecure and protected grad student self. Back then, in the forest. We collect hundreds of images. I didn’t even look at them anymore.

Part 3: The tenure-track temerity

On July 14th 2012 the space telescope Kepler broke. Not the telescope itself, but one of its four reaction wheels, the motors that keep the satellite precisely in the same position and prevent it from spinning. Kepler is a telescope that was staring on one patch of sky since 2009. It is basically doing the same thing I did on Calar Alto ten years earlier, just without rest and with much better precision. Kepler’s mission is to find planets eclipsing their host stars, many of them. It was extraordinarily successful, until 2012. And on 11th of May 2013, another reaction wheel broke. The original Kepler mission was over. But even with only two reaction wheels the space telescope can do useful things. The new mission, ingeniously called Kepler-2, will monitor fields around the ecliptic, each field for about two months, with reduced precision. In fact, this new mission turns out to be very useful for me. It will cover star forming regions, nearby stars, brown dwarfs, and open clusters. Among others: the Pleiades.

In December 2012 I was offered a position in St Andrews, the first job that wasn’t just a fellowship but something solid, with future and everything. In the meantime, the telescope in Tautenburg was more than 50 years old, the one in St Andrews as well, and I’m too old for the postdoc life. When I got the call with the job offer, I was standing in Killin in the Scottish Highlands. The mountains are cold and covered with snow. The next day I managed to get into an avalanche for the first time in my life. It was a tiny pathetic avalanche, but what the hell. As long as you are a postdoc, you are in a conflict. On one hand, you want the permanent job, to end the eternal uncertainty. On the other hand you know that the permanent job also means that you don’t have time for the postdoc life anymore, this uninhibited period of wild research. The actual research becomes a luxury, a kind of hobby after teaching and administration. The only option to continue to be a researcher is to stop being a researcher. We hunt for something that we don’t really want. But you cannot remain postdoc forever. We all have to grow up, some day.

Just from the data we had at this point, it was quite clear that the companion of R has to be dark, in comparison with R itself. There are two independent arguments supporting this conclusion. First, the eclipse is similarly deep in different parts of the electromagnetic spectrum, at 0.8 micrometer and at 1.2 micrometer. It is independent of colour. If a red body eclipses a yellow body, the colour of the entire thing would change during the eclipse. Not so if the eclipsing body is dark, or at least much darker than the primary object. Also, R, seen outside the eclipse, is just as bright as you would expect for a single brown dwarf in the Pleiades. A binary brown dwarf with one eclipsing the other would be twice as bright as a single brown dwarf. It is not. So, we are looking for something that does not emit more than a few percent the light of the R-star itself. Unfortunately, the luminosity of brown dwarfs drops steeply with mass. Even a object with half the mass of R itself is not expected to emit any light we could detect. These arguments do eliminate the option that we are looking at a brown dwarf binary with two equal mass components. The component has to be either a low-mass brown dwarf or a planet. That’s what it seems to be, anyway.

It wasn’t immediately clear to me what Kepler-2 meant for my R-story. But then it dawned on me. This is maybe the last, final, ultimate chance to get out of this number in a way that makes sense. Kepler-2 will provide a fantastic lightcurve for R — seventy days of continuous coverage, no daytime gaps, no weather interruptions, no sleep-deprived observer. Seventy days of clean, regular photometry, one datapoint every 30 minutes. It can be expected that we will see the eclipses in this lightcurves, in unbelievable accuracy, and my discovery from 2002 will be confirmed, finally. There is just no place to hide if you observe such an object for 70 days, so I thought. I just gotta publish the whole thing quickly, before anybody else checks what’s going on. I will just say that we were waiting the whole time for this confirmation. Which is true of course, in a way. It will be a demonstration of clean, painstaking, tedious, scientific work. A decade of hunting finally rewarded. Yeah, right. I can already see the headlines.

“Astronomers solve problem after fifteen years of observations.” “A discovery fifteen years in the making” — That’s the headline. But that’s not the only option. It is possible that K2 will show the eclipses clearly, more than once, maybe even the secondary eclipse, when the second body goes behind the first. In that case the K2 lightcurve will be totally sufficient to figure out the system, and our own data is redundant. If that happens, everybody can publish this thing and we might not be fast enough. The second option is just one eclipse, one. This would put us in a powerful position, because combined with our own data from 2001 and 2002 we could get the period, but nobody else. And finally it is possible that the K2 lightcurve will show absolutely nothing. It might really have this mysterious 363 day period and Kepler observes only for 80 days. It is possible.

Do I still need R? I had to think about this for a while, but of course you always need eclipses. First for scientific reasons. A part of me, in 2013 a surprisingly small part, really wants to know how large brown dwarfs are. On the other hand I could use R to justify my job. In 2017 some person I don’t know will decide about my job, following criteria I don’t know. Someone will push a button, and the money will either continue to flow or just stop. In 2014 I bought a house at the sea. I don’t want to move anymore. More money would help with that. That’s pretty absurd, isn’t it, a brown dwarf, something that nobody really knows, fourhundred fourty lightyears away, may support my silly lifestyle with the house, the sea, the rolling fields. But the timing would be perfect. The great discovery paper for R would come at the right time.

In February 2015 NASA approved my proposal to monitor brown dwarfs in the Pleiades with Kepler-2. Cunningly, I wrote the proposal without mentioning R at all. I just included it in a much longer list of targets and pretended that our goal is to measure rotation periods. Just like 2002. I’m so brilliant. The satellite slewed into position on February 7th, to stare at the Pleiades. From early February 2015 until April 26th it didn’t change its position relative to the stars. The data starts flowing. Dawn, the confidante from Granada, bearer of the secret, and now mother of an infant son, is paid by NASA to analyse the data. Over the summer of 2015 I prepare a paper, with the eclipse discovery in 2002 and an empty section for the confirmation from Kepler-2. A paper with a missing chapter. When the K2 data will eventually come out, we are going to do it. Finally.

There is a third reason why I still need R: shame. I carry too much shame with me anyway, all the time, and it would be nice to get rid of the additional load of shame that is caused by R. I didn’t become scientist to just sit on discoveries or to keep secrets. My self-perception as a scientist is in conflict with this dark secret in my drawer. It is an open wound that I have treated miserably over the years. It won’t heal before R is published. Ironically my self-perception has no problem at all with the idea of getting all the fame for myself.

The year 2015 was a breakthrough year for our understanding of R. While preparing for the Kepler-2 lightcurve, I basically re-analysed everything again. The most important result: The eclipse from 2002 stands. It didn’t disappear, just because nobody had looked at the data for a decade. I also had another look at our old data from 2001, the crappy second eclipse in the images from Tautenburg. That one looked odd. It was definitely shorter than the one in 2002, more like half an hour, really only two or three datapoints. How is that possible. Two options: Either it’s not an eclipse at all, but nonsense. The data is bad, after all, R barely visible. Or the eclipses are in fact evolving in front of our eyes. Okay, that’s seriously weird, but not impossible. Stranger things have happened.

One other thing happened: I lifted the secret, gradually. I told my parents. I told one or two other friends. I even told one or two astronomers, in confidence, without giving the object name away of course. It was still a secret.

While looking at everything again, I thought I check our spectroscopy again as well. It turns out, ESO had processed our spectra automatically. Since 2011 not only the raw data, but also the completely extracted and calibrated spectra were in the archive. That was kind of a surprise. It also saved me a lot of work. The spectra were bad, okay, lots of noise, but two absorption lines, the Sodium doublet at 820 nanometres, were clearly visible. I knew all along that these must be the most prominent absorptions lines in the red part of the spectrum and hence the best chance to get radial velocities. I cooked up a little routine to measure their positions with respect to the laboratory wavelengths, converted to velocities using the Doppler effect, and, well. Hard to tell. But if I average the measurements done in October 2003, it’s around 3km/s. If I average the ones from January 2004, it comes out at around 10 km/s. That’s a little more, even with the large errorbar. It might be that these spectra tentatively show radial velocity variations in the order of magnitude of a few kilometers per second. Which would be a pretty massive companion. Not Jupiter, not Saturn. Something heavier, like a ten or twenty Jupiter mass bolide.

And then the Kepler-2 data came out. It was Friday, the 4th of September, 2015. For weeks I had checked the archive, every day, and it was kind of a surprise when all of a sudden there was a lightcurve. I was sitting in my house, in pyjamas, tired, barely awake. The lightcurve in front of me. The lightcurve was noisy, all right. But it didn’t show anything. Not a damn thing. No eclipse, nothing. I turned the dataset upside down and still nothing. It wasn’t there. I paced through my hallway. It is a very long hallway, 20 or 30 steps. I walked back and forth. I stared out of my windows, all of them. What the hell. All this for absolutely nothing. What the hell is going on. I spent the day at home, wandering along the sea, sitting on rocks. Laughing at myself, but also cursing at the sky. Why are you doing this to me. Why. It was one of the most remarkable, one of the most frustrating days of my scientific life.

With that, we are at square one. Well, not exactly. At least we can now definitely rule out all periods from 0 to 80 days. Not bad.