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Thaisa Storchi Bergmann

Thaisa Storchi Bergmann: The neighborhood of black holes

For over 30 years, the astrophysicist from the south of Brazil has focused on understanding how black holes get their energy

BRIGITTE LACOMBEInfluenced by a cousin, the astrophysicist Thaisa Storchi Bergmann, born in Caxias do Sul, Rio Grande do Sul State, almost became an architect. Following in the footsteps of her relative, she studied architecture for a semester at the Federal University of Rio Grande do Sul (UFRGS) in 1974, but she quickly switched to physics. Today a full professor at the UFRGS Physics Institute, she is one of the most respected specialists on supermassive black holes. The term refers to extremely compact regions of space, located in the center of most known galaxies, where gravity is so strong that nothing escapes, not even light. The mass of these mega-structures that suck up all the matter around them may be millions or billions of times larger than that of stellar black holes. The latter are the source of the gravitational waves—predicted by Albert Einstein—detected by the LIGO (Laser Interferometer Gravitational-Wave Observatory) experiment last year. (see report with new findings from that project).

Storchi Bergmann became internationally known in her field when she published a study in 1993 in which she provided indirect evidence that there was an active supermassive black hole in the center of galaxy NGC 1097. This galaxy is of the LINER type. Its nucleus is active: it emits radiation whose nature cannot be attributed to stars, but rather to the capture of matter by a black hole. However, unlike most active galaxies, the LINER-type have low luminosity and emit less ionized gas (i.e., the oxygen and nitrogen atoms have not lost many electrons). In the article, the researcher reported evidence of the presence of a flat, ring-shaped cloud of hydrogen in a plasma state (protons and free electrons) revolving at 10,000 km per second (km/s) around a central point in NGC 1097. In astrophysicist jargon, the cloud is called an accretion disk of matter. “For a gas cloud to revolve at that speed around a point in a galaxy, the only explanation is the existence of a black hole,” the astrophysicist explains. Until then, there was only evidence of these phenomena around radio galaxies, which are much more active than LINER-type galaxies.

In 2015, she was one of the five winners of the International L’Oréal-UNESCO awards for Women in Science. The honor made her better-known outside astrophysics circles. “Even friends and family members became aware of the importance of my work,” she says. In the interview, the astrophysicist, who is married and has three children, talks about her research and career.

Extragalactic astrophysics, focusing on the study of supermassive black holes
Undergraduate degree in physics from ufrgs (1977), master’s degree in physics from puc-rio (1980) and phd in physics from ufrgs (1987)
Scientific production
140 published articles, advised 15 master’s students and 14 phd students

Your most-cited article on black holes is from 1993. Why is it important?
The article was influential because it described a discovery. It was the first time we had found evidence of the presence of an accretion disk of matter spinning around the nucleus of a LINER-type galaxy. The existence of this disk is evidence that this type of galaxy, which is less luminous and less active than radio galaxies, has a supermassive black hole in its nucleus. In the emission spectrum of NGC 1097, in the set of frequencies of the electromagnetic radiation emitted by the nucleus of this galaxy, I found a specific energy profile that is only produced by hydrogen atoms when associated with the presence of an accretion disc. This profile, which we technically call a double peak in the emission of H-alpha and H-beta energy lines, had previously been detected only in quasars and radio galaxies, which are much more active than LINER galaxies. At that time, astrophysicists thought that only objects with very active nuclei, such as radio galaxies, had a black hole in their center. Today, we accept the idea that most galaxies, including the Milky Way, which does not have an active nucleus, have a black hole.

How did you become interested in galaxy NGC 1097?
I had completed my first postdoctorate in 1991, under the supervision of Andrew Wilson of the University of Maryland, but there were still some projects to complete at the Inter-American Observatory on Cerro Tololo, Chile. At the time, Tololo had one of the largest telescopes in the world, with a 4-meter diameter mirror. Wilson was studying a set of active galaxies that had gas rings around their nuclei. He even teased me. He said women loved rings. Therefore, we would study galaxies with rings. We studied the movement of the gases in the ring in these galaxies using spectroscopy techniques [methods measuring the wavelengths of electromagnetic radiation emitted by celestial objects, from which astrophysicists infer some properties of these bodies, such as temperature, chemical composition and mass]. We wanted to see what the gas dynamics in the ring were like. It looked like it was spinning faster. We also wanted to investigate whether there was evidence that the gas was moving out of the ring, feeding the active nucleus of the galaxy.

What is the connection between this energy emission pattern and the gas ring?
The double peak is the spectral signature of the rotating gas, i.e., of the presence of a moving disc or ring of gas. In cataclysmic variable stars [systems of variable brightness consisting of two stars that are very close to each other, in which the smaller star loses matter to the larger], this double peak is also seen. But the speeds we saw in NGC 1097 were about 10,000 km/s. Only the presence of a supermassive black hole would cause a gas cloud to spin at that speed around a point in a galaxy.

No one had studied that galaxy before?
At that time, the concept of a LINER—a galaxy with very low activity and weak ionic emission—was new. NGC 1097 had already been observed by an American astrophysicist, Mark Phillips, who worked at Cerro Tololo in 1985, but he had not seen this double-peak profile. The radio galaxies were more powerful, emitting jets of waves and X-rays, and the only way to explain this level of activity was a black hole. In LINER-type galaxies, we did not have this certainty. They have weaker emission lines and it is not obvious that they need a black hole to explain this degree of activity. Now that I have been observing this galaxy for more than 30 years, I know that I was lucky to record a transient, infrequent phenomenon. Something led the galaxy to form this accretion disk. A gas cloud or a star was captured by the galaxy and I was fortunate enough to see that signature of the gas spinning around the black hole before falling into it.

Stephane Cardinale / People Avenue Poster in Paris with a photo of Thaisa Storchi Bergmann in 2015: recognition for her contributions to scienceStephane Cardinale / People Avenue

So the accretion disk cannot always be seen around this galaxy?
Nuclear activity occurs when there is material to feed the black hole. In this case, an accretion disk forms and heats up. The current paradigm is that any level of nuclear activity, low or high, results from the capture of matter. In LINER-type galaxies, which emit little light, not much matter is captured. In quasars, a lot of gas is captured, because they were formed at a time when there was a lot of gas available. In this case, a larger, brighter accretion disk forms. Since then, I have been monitoring and seeing the accretion disk change in NGC 1097, and more recently in other galaxies as well. The disc “turns off” and “turns on.” Two or three years later after this, which was my first paper, several researchers with access to the Hubble Space Telescope published papers on double-peak-profile LINERs. It is difficult to record this profile from ground telescopes, because you have to separate emission from stars from the gas cloud emissions. To do this, you need the best possible image quality, like that of Hubble, which is above the Earth’s atmosphere.

What other important contributions would you highlight in your scientific output?
There are two studies in which I was involved, although not as the main author, that are much more cited than my studies on black hole accretion discs. One was in 1994 with Daniela Calzetti of the University of Massachusetts, and Anne Kinney, who was then working at the Space Telescope Science Institute and is now at the Keck Observatory in Hawaii. I performed the optical observations using the Cerro Tololo telescopes that were included in a spectroscopic atlas of galaxies for which they compiled ultraviolet data from the International Ultraviolet Explorer (IUE) satellite—the best available for this type of observation before Hubble. Ultraviolet radiation is important for studying the emission of young stars, meaning those less than a few million years old. By combining optical and ultraviolet observations, we constructed templates—mean spectra—for different types of galaxies. These templates are still used today at different observatories around the world. They are used to calculate how much observation time is needed to obtain a desired spectrum from a galaxy. Therefore, they are used to prepare observation proposals sent to observatories.

And the other article?
Daniela Calzetti had worked with interstellar dust in her dissertation and we had the idea of studying the dust in the galaxies of our atlas through the spectral emission lines. Dust extinguishes starlight, but selectively. It attenuates the blue more than the red. A dust-free spectrum is the bluest of all. We then created an alternative method to study the attenuation produced by dust: a law that calculates and corrects the spectrum to take into account the effect of the dust in the starburst galaxies, which have intense star formation. There are more than a thousand citations of this paper, which Daniela and I worked on together.

How did you become interested in science?
I have liked science since I was a child. I was that diligent student who got good grades. I started studying at a private, religious school in Caxias do Sul. For high school, I attended a public, state school. That is when I became more deeply interested in science. I asked for a microscope as a gift and set up a chemistry lab. My father bought a very powerful microscope and set up a laboratory in the attic, essentially a work table and shelves where I placed the microscope and some chemical solutions. For me, being a scientist was playing with the test tubes, creating reactions. I even had a partner in the lab, Vera, a schoolmate. We had class in the morning, and in the afternoon we would sometimes get together to do some schoolwork and play in the lab.

In what fields did your parents work?
My father studied accounting and was a partner in a lumber company that made wooden crates and, later, plastic crates for beverages. My mother was a primary-school teacher. She liked to read a lot, but was not interested in science. Only I was. Maybe I had good teachers who encouraged me.

When did you become interested in astrophysics?
When I took a course called Physics for Architects during my first semester at university in 1974, when I began my degree in architecture at UFRGS. I had a cousin, two years older than I was, who was passionate about the field. I got swept up by her excitement, took the entrance exam and was admitted. When classes began, I realized that architecture was not my dream. At the time, the Physics Institute was in downtown Porto Alegre, near the School of Architecture. Our physics classes were held there. I saw people in the laboratory and realized that what I really liked was research. At the end of the first semester, I requested a transfer to physics.

You just asked and they let you change your major?
It was easy back then. You needed to find someone in the new major who wanted your spot in the old major. There were five physics students interested in changing to architecture. It was easier to move to physics than to architecture. They had a competition to decide who would get my place. In the second semester, 1974, I became a physics student. I graduated in 1977.

Was there an astrophysics department or major at the institute?
There was Professor Edemundo da Rocha Vieira, who was interested in astrophysics, with a doctorate in radio astronomy from Argentina. He was very active and the institute, to establish itself as one, needed another department. It had a physics department, and Edemundo established an astronomy department in 1971. The first professors hired were two Argentines, Zulema Abraham [now at the University of São Paulo] and Federico Strauss. Later, in 1978, Edemundo brought Miriani Pastoriza from Córdoba as a visiting professor, and she played an important role here. She was one of the first Latin American women to do research in astrophysics. Before the construction of the American observatories in Chile, the one at Córdoba had the largest telescope in South America. Miriani, today an emeritus professor in the department, together with her PhD advisor, J.L. Sérsic, discovered and described a type of spiral galaxy, with star-forming regions around a central point. These galaxies, with peculiar nuclei, are now called Sersic-Pastoriza galaxies. In the end, Edemundo also brought over me and Kepler de Oliveira, my undergraduate physics classmate and now a professor in the department. We were the best students in the class and Edemundo wanted us to do astrophysics research.

Did you start your master’s degree right after graduation?
I graduated, got married and my husband, who is a chemical engineer, went to do a master’s degree in Rio de Janeiro. So I studied for a master’s degree in astrophysics in Rio de Janeiro. I was there for two years, 1978 and 1979, and then I returned to UFRGS. I did a master’s degree at PUC-Rio and at the National Observatory with the American astronomer William Kunkel, who was helping set up the National Astrophysics Laboratory (LNA).

Were you already interested in black holes?
Not yet. During my master’s degree, under Kunkel’s direction, I did more mathematical work, with data he already had from a photometric filter system for measuring star radiation. Near the end of my master’s work, he told me that if I had the opportunity, I should study the galaxies, which he said were more fascinating. That stuck in my mind. Back in Porto Alegre, I talked to Miriani, a person always full of ideas. We even tried to observe galaxies through the LNA telescope, but it did not have a spectrograph at the time. Miriani had done a postdoctorate in the United States and knew the director of Cerro Tololo. We sent him a letter asking for some observation time for our work with galaxies. We did not know if our request would be granted because Cerro Tololo was for U.S. use only. He replied yes, but asked us to prepare a proposal for observations using the observatory’s small telescope, which had a 1-meter-diameter mirror. During that period, I began doing spectroscopy of galaxies for my PhD. Miriani was interested in active galaxies. We chose a sample of this type of galaxy and used the spectra obtained from Cerro Tololo. I studied the chemical abundance and physical conditions of their central regions. I came to the conclusion that they had an excess abundance of nitrogen and of almost all heavy elements in their nuclei.

What does this excess mean?
We wanted to see what was different about these galaxies. The Sun is our reference. It is 70% hydrogen, 26% helium and 4% chemical elements heavier than hydrogen and helium. We, astrophysicists, call all elements heavier than hydrogen and helium—such as carbon, oxygen, and nitrogen—metals. These metals are synthesized inside the stars. The more generations of stars in a galaxy, the more enriched, the more abundant, these metals are. Compared with the Sun, the center of the active galaxies was more evolved, that is, they had undergone greater chemical processing. At that time, as we did not know what nuclear activity in galaxies meant, we attempted to establish a relationship between this parameter and chemical abundance. Today, we believe that, regardless of whether a galaxy is active or not, its nucleus has a higher chemical abundance than that of the Sun. This is because the sun is not right in the middle of the Milky Way. It is further away from its nucleus. There is, therefore, a metal gradient between the different regions of a galaxy. We went to Chile three times to perform observations. During the last, a rare astrophysical phenomenon occurred.

In 1987, Miriani Pastoriza and Thaisa Storchi Bergmann (right) observed the rare explosion of a supernova in Chile and appeared in the New York Times

What happened?
In February 1987, one day before we arrived on the mountain, the 1987A supernova exploded about 170,000 light-years from Earth. There had been no record of a supernova exploding so close to the Earth since the 16th century. A Canadian astronomer, Ian Shelton, was at the Las Campanas Observatory, not far from Cerro Tololo [about 240 kilometers away], developing photographic plates taken of the Magellanic Cloud, which were best observed in the middle of the night. When he developed the plates, at dawn, he saw that there was a ball in the images. He ran from the laboratory, into the street. He knew that, if the ball was due to the explosion of a star, it would be visible to the naked eye. And it was.

What did you and Miriani have to do with this story?
The news of the supernova explosion spread rapidly. The following night, there were already reporters and astrophysicists from the United States in Chile to observe the phenomenon. As we were preparing to climb Cerro Tololo and start our observations, we were told that the 1-meter telescope we were going to use was the best to observe the supernova. The star was so bright that it made no sense to use the 4-meter telescope, best suited for observing less brilliant objects. So, every night for a week, I had to first observe the supernova for about three hours, then my galaxies. It was great. We were interviewed and even appeared in the New York Times. The reporter was amazed to see two women doing astrophysics on a mountain in Chile.

Sometimes the careers of women in science take a little longer to move forward. Would you say that was your case as well?
It happened to me. I had two children right away, taught at the university and worked on my PhD at the same time. I started my PhD with Miriani in 1981 and only defended my dissertation in 1987. It was a difficult time. As much as husbands are theoretically partners in raising children, when a child becomes sick, the mother always does the lion’s share of the work. There is a sort of tacit agreement to that effect. My husband traveled a lot. Thank goodness I was able to hire help and I also had support from my mother, who was already retired, with the children during that period. When I finished my doctorate, my children were 5 and 6 years old.

Has the situation of the female researcher changed much in astrophysics over the last few decades?
It has changed less that I would like. At international conferences, I see a lot more women now, but there are still few in top positions at institutes. I always felt respected and well-treated. I think I even receive more attention due to being a woman. I’m not saying I never suffered prejudice at any point. In a subtle way, this always occurs. My colleagues abroad were always curious, since I was a woman from Brazil. I think that, even today, a woman’s biggest obstacle is reconciling a career with raising children. I still remember a rather complicated situation I went through. In 1997, I requested observation time on the 4-meter Cerro Tololo telescope with Andrew Wilson. I did not know that I was four months pregnant with my third child when I sent the proposal. It was accepted, and when it was time to go to Chile, I was breastfeeding. They told me that I could not bring a baby to the observatory. Astrophysicists make observations at night and sleep during the day. A baby in the observatory housing would keep them awake. But I really wanted to go. I insisted so forcefully that they found a house for me near the observatory, which had been used by the engineers who had built the observatory. I had to bring a nanny to help. They called me at the observatory when the baby cried so I could go down and breastfeed it.

Did winning the L’Oréal prize in 2015 make a difference in your life?
This prize is also from UNESCO, but my scientific colleagues view it as being only moderately important. But the repercussion outside the scientific milieu was enormous. Not a week goes by without my receiving a request for a lecture or interview. I have to refuse some requests due to lack of time. Even friends and family began to see our work differently. When I was in Paris to receive the prize with two of my children, I noticed the pride they felt when they saw those huge posters with their mother’s photo at the airport and other locations around the city. Looking back, perhaps today I would not do everything I did in the past. But, if I had not, I also would not have received the recognition that I have. I think I even missed out a bit on my children’s childhoods because of how involved I became in my career. I think I overdid it a bit. I accepted every project that came my way. I could have done less, with less stress.

What research are you doing now?
I continue to study accretion disks in galaxies with black holes. I am on the board of the Gemini telescopes, and I use them a lot to study gas flow in and out of the region near supermassive black holes. I am also working on a project using Hubble data. I am collaborating with a Chilean researcher to use the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope to study how the accretion disk captures matter in active galaxies. I still participate in the ALMA proposal screening process and I also collaborate on the Mapping Nearby Galaxies at APO (MaNGA) project, a survey of the spectra of 10,000 galaxies, which is part of the Sloan Digital Sky Survey.