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Interview

Augusto Damineli: Stellar interpreter

An astrophysicist recounts his discovery that the most-studied star beyond our Sun undergoes periodic dips in luminance, and is actually a system composed of two stars

Léo Ramos Chaves

Every five and a half years, astrophysicist Augusto Damineli has an appointment that can’t be rescheduled: for six consecutive months he observes the strange and enigmatic Eta Carinae, the most-studied star beyond our Sun, some 7,500 light-years distant from Earth. It’s a date he’s been keeping since the early 1990s, when the professor at the Institute of Astronomy, Geophysics, and Atmospheric Sciences at the University of São Paulo (IAG-USP) challenged the skepticism of international colleagues and proposed that Eta Carinae has two defining features, which are now accepted and well established in the scientific literature on the subject.

His first contribution explains the unstable behavior of Eta Carinae, which has demonstrated energy fluctuations since the 19th century, sometimes accompanied by major dips in luminosity. Damineli found that the star dims for approximately 90 consecutive days at the wavelengths of X-rays, ultraviolet rays, and radio wave frequencies (but not visible light) every 5.54 years. During this periodic dimming, the star’s energy emissions diminish by the equivalent of 20,000 suns. This phenomenon occurs—and this was the astrophysicist’s second proposal—because Eta Carinae is, in fact, a binary system, composed of two stars. The larger star has a mass of 90 suns, while the smaller of the pair has a mass of 30 suns. During the periastron, the closest point between its orbits, some of the emissions from the larger Eta Carinae are blocked by the intrusive passage of its younger sister, as observed from Earth.

In mid-February of this year, as foreseen, the Eta Carinae system began to exhibit its selective dimming. Damineli is ready once again, and is keeping an eye on the data being collected by identical automated telescopes, one installed in Chile and the other in South Africa. For the first time, he won’t need to go into the field to take measurements. “I’ve programmed all the observations through November,” he says, with a mixture of happiness and relief. “I don’t have to stop teaching so I can travel. I can even go out to my little ranch, where I have satellite internet, and still see if the telescopes have captured data.” In this interview, the astrophysicist talks about his research on Eta Carinae and recalls his career, which included growing up in the country, and living at a seminary, before ending up in academics.

Age
72
Field of expertise
Massive stars
Institution
University of São Paulo (USP)
Education
Degree in physics from the USP Institute of Physics (1973), master’s and doctorate from the Institute of Astronomy, Geophysics, and Atmospheric Sciences at USP (1976 and 1988)
Literary output
78 scientific articles

When was the first time you heard of Eta Carinae?
It was through Professor José Antônio de Freitas Pacheco, the first head of the USP Department of Astronomy. It must have been around 1978. I remember that we took the first electromagnetic spectrum measurements of Eta Carinae at the Abrahão de Moraes Observatory, in Valinhos [São Paulo]. It was incomprehensible, with a lot of data. At that time, I knew that it was the most-studied star beyond our own Sun. There was a lot of literature about it in the library. I also knew that it had undergone a huge explosion, like a supernova, in the 1840s, but that, instead of dying, it had survived the event. Everyone wondered how that could have happened. Supernovae explode once, then die. Eta Carinae was a mystery that various important people had researched, but no one had been able to solve. Since Eta Carinae was the only star with this type of behavior, it wasn’t possible to compare it with any others. It was an outlier.

Had you studied Eta Carinae before, while doing your master’s or doctorate?
No, but I had worked with binary stars under Pacheco’s supervision. I graduated in physics at USP in 1973 and studied binary X-ray stars for my master’s in astrophysics. For my doctorate, which I finished in 1988, I studied stars with more than eight solar masses that die as supernovae. I became interested in these stars because they produce oxygen.

Where does this oxygen go?
It goes into the interstellar medium, where second-generation planets and stars like the Sun are formed. Eta Carinae is something that should no longer exist. According to physics, it should have died in the big explosion. Therefore, it’s a window for revisiting the distant past. It’s like having a dinosaur, today. But the problem is that at that time there was no way to study it. It’s surrounded by a nebula, a long cloud of gas and dust, which we call homunculus, and emits a lot of complicated spectral lines. In the visible light spectrum, we can’t see either of the two stars in the system due to the presence of the nebula.

What are spectral lines?
They are channels of energy. On television and radio, information arrives through different channels. The atoms of a star’s chemical elements, such as iron, hydrogen, and helium, concentrate their spectral lines in certain channels. To read messages from the stars, we need to analyze the emissions of their atoms. An astronomer’s life is spent looking at various spectral lines of stars, from which we deduce their temperature and composition. A star is an orchestra. It can emit a little bit of everything at the same time. We try to find out which instruments, that is, which atoms are “playing” at the time we observe them. For example, if there are lines emitted associated with ionized hydrogen, the temperature has reached about 10,000 degrees. If it’s ionized helium, it’s hitting 30,000 degrees.

When did you start studying Eta Carinae in a more systematic way?
In Brazil, around 1987, I was the only one working on high-mass stars, those with more than ten solar masses. I’d been a professor at USP since 1976. I felt like a fish out of water. Through Pacheco, I met an Italian astrophysicist, Roberto Viotti, who worked with high-mass stars and had done his doctorate on Eta Carinae. My life here was kind of complicated. I had separated from my first wife and was looking to leave. I decided to do a postdoc with Viotti in 1988 at the Space Astrophysics Institute, in Frascati, near Rome.

Personal archive With his two brothers, Damineli (circled) poses with parents Salvatino and Ida at Christmas in 1955, in Ibiporã, ParanáPersonal archive

Were the research conditions there good?
More or less. I didn’t know that Italian science had been completely dismantled. There was virtually no public funding for research institutes. There was only money, and very little, for universities. Furthermore, when I got there, I found that Viotti didn’t know what else to do to study Eta Carinae. Then I learned that a modern spectrograph detector had been purchased for the 1.6-meter telescope at the Pico dos Dias Observatory, run by the National Astrophysics Laboratory [LNA], in Minas Gerais. From Italy, I asked a Brazilian colleague to obtain a spectrum from Eta Carinae. I wanted to test the new equipment. In the analysis, an interesting emission appeared in one spectral line in the infrared, in a channel associated with helium. At that frequency, the star had emitted energy equivalent to that of hundreds of Suns. But we didn’t know how to interpret this result. I learned what there was to learn from Viotti in spectroscopy and, in 1990, I finished my postdoctorate and came back here.

What did you do next?
I started observing the star at other wavelengths. I’d read that at certain times Eta Carinae temporarily stopped emitting all of its high-energy channels. This type of phenomenon is normally seen in the ultraviolet, but we didn’t have access to a satellite to observe it at that wavelength. So I used the “poor people’s satellite.” I went to the LNA observatory and tracked the energy emissions in an infrared line that behaves similarly to the high-energy ultraviolet channels. If the ultraviolet emissions disappeared, something similar should also happen in that infrared line. In May 1992, that line began to disappear and in June the emissions went to zero. I turned to Viotti, in Italy, who had access to a satellite that could make observations in the ultraviolet, but he didn’t trust my data. He said he had a career to look out for and that observations made using electronic equipment below the equator could play tricks. In other words, Brazilian data had to be viewed with some reservation.

This wasn’t the only time that your work on Eta Carinae was questioned.
At international conferences, when I said that my data had been obtained at the Pico dos Dias Observatory, my colleagues couldn’t believe it. I showed them pictures of the observatory and they were surprised by the numbers of banana trees on top of the hill. They said it was a jungle telescope. They hadn’t heard of Brazilian astronomy; they only knew our soccer. I realized that I had to come up with something more solid to convince them, so I made a prediction that the phenomenon of a dip in emissions would happen again.

What did you base your prediction on?
I used data from my mid-1992 observation, and compiled information on various instabilities in Eta Carinae’s spectral line emissions recorded in the past. I compared the dates of the other dips, made some calculations, and saw that every five and a half years the phenomenon seemed to repeat itself. In 1996 I published a science article in which I predicted that another dip should occur between the end of 1997 and the beginning of 1998. The prediction stunned the skeptics. The person who promoted my research the most was Kris Davidson, from the Minnesota Institute of Astrophysics, who, at first, didn’t believe in my study.

How did he view the Eta Carinae system?
Davidson had shown that Eta Carinae wasn’t a star being born, as many thought, but one that was dying. However, he thought it was a single star and that the proximity of its death was causing the dimming periods. Nor did he believe that it was actually a periodic phenomenon. Despite our disagreements, he and I together asked for time on the NASA Space Telescope to observe Eta Carinae. I had my neck in a noose. If the dip didn’t occur, I would be demoralized. That 1996 paper has almost 400 citations today. To reach that number of citations, it must have impacted on other related areas. The discovery that Eta Carinae was two stars led to an idea that’s now widely accepted, that most stars with more than ten solar masses are systems with two stars. We haven’t yet seen Eta Carinae’s smaller companion directly, only indirectly, but the system’s double nature is now accepted by everyone.

Eta Carinae is a thing that should no longer exist. It should have died in the explosion. It’s like having a dinosaur, today.

What evidence did you have that Eta Carinae was really two stars?
The periodicity of the spectral dimming indicates that there is a mechanical, binary mechanism behind the phenomenon. Something similar to an eclipse, which is related to the orbits of two celestial bodies, like Jupiter and its moons. Beyond that, we also had data that Eta Carinae was emitting two very different types of emissions simultaneously, one low energy and the other high energy. These data were indications that there were two stars, one low temperature—larger and colder—and another smaller, warmer, high-temperature star. The smaller star undergoes the dips in emissions. A system with two stars creates an observation calendar, similar to what happens with solar and lunar eclipses. You don’t have to spend five and a half years tracking the star. You just need to observe it for six or eight months during the periastron, when the interaction between the two stars is biggest and they “speak.” Since ancient times, eclipses and similar phenomena have been a device for producing information to guide our rationality. Today Eta Carinae is studied at all wavelengths, from gamma rays through the visible and radio spectra, to the infrared.

What’s happening to the two stars during these dips in emissions?
The smaller star dives through the atmosphere of the larger one, from which it pulls matter. This phenomenon is observable in the ionized helium emission lines. The orbit of the smaller star is highly eccentric, elongated, like that of Halley’s comet. This means that at its periastron, it comes very close to the larger star. Some comets have orbits so eccentric that they end up being swallowed by the Sun. With stars, this is a phenomenon that we haven’t yet been able to describe very well. It’s likely that the instabilities and eruptions recorded at Eta Carinae in the past occurred during these close passes by the smaller star. Today we know that during the periastron, Eta Carinae ceases to emit energy primarily in the X-ray range. Then other high-energy channels fade out, but not all. In the visible light spectrum, it appears that nothing has happened to the system.

Can you predict when Eta Carinae is going to die?
The larger star still has enough hydrogen to burn continuously for another 500,000 years. We’ve only recently become aware of about half a dozen systems similar to Eta Carinae, all located in other galaxies. According to these few examples, some massive stars may disappear within a few years after showing energy instabilities. But there is no established theory regarding the evolution of this type of star. It seems that some very bright ones die before depleting all their hydrogen. But everyone will know when Eta Carinae explodes and dies. The brilliance of its death will surpass that of our entire galaxy. At night, it will be as bright as ten full moons. You’ll be able to see a needle on the floor.

Why did you decide to be an astrophysicist?
I was born in Ibiporã, near Londrina, Paraná. I’m the tenth of eleven children in a farm family. My mother was illiterate. My father, who’s own father was Italian, only made it through elementary school, but he liked math. We lived in the country and, like my brothers, I had to walk barefoot eight kilometers each way to get to school, which was in town. I studied at a convent school, paid for with milk that I took to class. The public school was really bad. At home, while I was doing my homework, I didn’t have to go to the fields. So, at the age of nine, the pencil started to be much more interesting to me than the hoe. My brothers said that I was useless, that I wasn’t good at hard work. They told me to keep studying. My family grew corn, rice, cotton, beans—a little bit of everything. It was an exchange economy, which hardly used money. We were poor, but we had plenty of food. When we needed some extra money, we did seasonal work harvesting coffee in the nearby plantations during winter.

Was your father’s liking mathematics an important influence?
My mother and my older brothers and I worked the fields. My father made a living by building houses. He could look at a log and know how many planks it would yield. Once, I got pneumonia. While he prepared the penicillin for me, my father would give me math problems to solve. For me, it was a fantastic time; math allowed me to have a special connection with my father. I started to like mathematics because of that. At that time, there wasn’t any other kind of conversation between a boy and a 50-year-old man.

Denying scientific evidence is a test of faith. People feel like they’re part of a flock

Why did you enter the seminary when you were still a boy?
It was the influence of one of the nuns at the school, Sister Benta. Going into the seminary was also a way to get off the farm and see a different world. I went to Assis, in the state of São Paulo, at the age of 12. My brother Mário, who was two years older, had gone to that same seminary earlier. But I didn’t know what it meant to be a priest. When I reached adolescence, around 16 years old, my world fell apart. I didn’t agree with much that the Church preached. I wasn’t going to be able to deliver a sermon. I didn’t have that much faith, I was more rational. In 1965, my father died. The following year, at the age of 18, I left the seminary. My brother would also abandon it later.

Was life in the seminary a bad period?
I didn’t like playing soccer every day. I preferred reading. But the seminary was a fantastic world. I would go to the library and read Dante Alighieri in the original. I had priest-teachers who were good mathematicians. Some colleagues at the seminary liked sociology and philosophy. I was into math, which was a more intelligible world. I liked to take things apart and put them back together, and to demonstrate theorems that had complicated formulas and only one way of solving them.

Did you move to São Paulo after you left the seminary?
No. I returned to Ibiporã, but, at that time, my mother was already living in the city. I found a job that required a bit of math. Actually, I did billing for a company and I had to know how to calculate the interest that customers owed. I entered the old science course at a public school that had been opened in the city, but I already knew almost everything that was taught. I didn’t know what I wanted to do with my life. At that time, in northern Paraná State, the best-known professionals were the engineers trained by Mackenzie, but I couldn’t afford that college. USP was unknown there. I had a good education, but knew almost nothing about how the world worked. I decided to do some private tutoring, something I had already done at the seminary, and I put together enough money to buy a suitcase and support myself for a month in the city in São Paulo until I got a job. That was in 1968.

You came here without a job?
I brought only a reference letter so I could work in the construction industry. I lived in a boarding house, and worked in a factory, and in construction as a foreman. It was a difficult time. When I arrived, there were a lot of people protesting and students were confronting the police. But I liked that. The world of the police was always distant to me, and I identified with the students. I went to high school at a good public school on Rua da Mooca and the high school student movement there was active. The physics classes were good, better than those in Paraná. But it soon became clear that I would need to do a preparatory course to enter USP. The Equipe college prep school had just opened, and I got a scholarship that gave me a good discount. That was when I found my team. I did the preparatory course in 1969 and entered the physics program at USP the following year.

Why did you become interested in astrophysics?
None of the specialties appealed to me very much. Nuclear physics smelled more like the atom bomb than anything else. Being a physics teacher didn’t appeal to me. I wanted to do something that would allow me to discover new things. I remember one day Professor Pacheco gave a lecture on supernovae and said that our atoms had originated from these explosions, from the deaths of these stars. I thought that was great. After the lecture, three classmates and I—João Steiner, Laerte Sodré, and Mario de Oliveira, all professors at USP today—went to talk to Pacheco. He said he could get me an undergraduate science scholarship to study these stars. That’s how I started. In 1973, Pacheco founded the postgraduate course in astrophysics at USP.

Nathan Smith / John Morse / Hubble Image of the Eta Carinae binary system, surrounded by a gas and dust nebulaNathan Smith / John Morse / Hubble

Brazilian astronomy has 1% of the world’s researchers and publishes 2.5% of the articles in the area. Has it reached its ceiling?
Despite this success, the size of Brazilian astronomy is still much smaller than that of other countries of equal economic weight, such as Spain, Italy, France, and Australia. We still don’t develop big projects, which entails having serious scientific instruments. When I started my career, astronomy in Brazil was just beginning. There wasn’t one large telescope at our disposal. I’ve participated in efforts over the last decades so we can get access to first-rate equipment, such as the Gemini Observatories, which have two 8-meter telescopes, and Soar, which has a 4-meter telescope. I’m about to leave the scene, but I see a very promising future ahead, based on the access we’ll have to the GMT [Giant Magellan Telescope] that’s under construction in Chile, which will have a 24.5-meter mirror. I won’t be using it personally, but I’m content knowing that current generations will be able to use 4% of its observation time thanks to FAPESP’s investment in the project. And what’s more, with access to the GMT, the state of São Paulo’s industrial sector will be able to produce state-of-the-art instruments like cameras and spectrographs for the super telescope.

Why, in addition to doing research, did you dedicate yourself to popularizing astrophysics?
For four years, between 1992 and 1996, I wrote a monthly column—four to six pages long—in the magazine Superinteressante. I have always worked on two fronts. One was to explain the everyday, what people see in the sky, the other was to explore current topics in astrophysics. Researchers have to communicate with those outside of science, in a simple way. If I can’t explain what I do concisely and directly to my wife or a layperson, I can’t rest. The democratization of science opens new avenues for people. My mission is to bring the sky down to earth. I like to point out that the success of agriculture came from celestial observation, which allowed us to master the mechanism of climatic seasons. Through studying the Moon’s importance, Newton developed differential and integral calculus, which are now used in engineering, and that’s had a huge impact on global GDP. We would be much poorer, intellectually and materially, if our moon didn’t exist. Without Sobral’s solar eclipse measurements in 1919, Einstein’s theory of relativity might not have been accepted yet [see Pesquisa FAPESP issue no. 278]. Our atoms came from the stars. We have a cosmic connection. I’m not the one who’s living with his head in the clouds, it’s the people who are unaware of that dimension.

What would you say to a flat-earther?
I can’t fight a flat-earther by demonstrating that the Earth isn’t flat. That is not the battle, it was demonstrated 2,500 years ago. It’s not a matter of argumentation. It’s a matter of faith, which doesn’t come from a lack of information. They gave up precious knowledge to follow a religion. Denying the greatest scientific evidence is a greater test of faith. The more they abdicate knowledge, the more these people feel they’re part of their flock. This is a well-known mechanism, which is also adopted by the anti-vaccine movement, by people who refuse to receive blood transfusions, by Holocaust and slavery deniers. These people blindly follow their leader. What can you do then? Offer opportunities to exercise rationality. You have to make people understand what a black hole is, or the four-dimensionality of our world. Science communication is a positive agenda that offers intellectual nourishment to attract people to a concrete reality. Once they understand this, people are vaccinated against this type of faith.

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