The Baja Astronomical Observatory, part of the University of Szeged since 2015, has been a center of astronomical research for six decades. Among the researchers based at the observatory is astronomer Tamás Borkovits, whose theoretical work played a key role in the recent identification of the most compact 3+1 hierarchical stellar system known to date. When we met him, he had just finished conducting an exam for SZTE master’s students in astronomy. How did a calculation he had developed with no expectation that it would ever leave his desk drawer become the key to solving an astronomical mystery? What does the daily work of an astronomer actually involve? And can scientific inquiry and spirituality coexist? These were among the central topics of our conversation.
Q: The observatory has a warm, almost family-like atmosphere. How many people are on the team?
A: We really are a small research institute – you have already met almost everyone on the research staff. At the moment, four astronomers conduct research here. Our team also includes a maintenance staff member, a librarian who serves as secretary and financial manager, and a computing specialist who provides research support and also acts as our systems administrator. That is essentially the entire institute. We are also regularly joined by Dominik Bánhidi, a University of Szeged PhD student in astronomy from Baja, and we very much hope that we will be able to offer him a permanent position in the future.
From left: Dominik Bánhidi, István Csányi (an astronomer who graduated from SZTE), Dr. Imre Barna Bíró, and Dr. Tamás Borkovits. Photo: Karina Bartha
Q: What are the Observatory’s main areas of research?
A: One of the research groups based at the Observatory is the HUN-REN Stellar Astrophysics Research Group, which I lead. Several of its members are also affiliated with the University of Szeged’s Department of Experimental Physics. At the Observatory, we all work on variable stars, with a particular focus on eclipsing binary systems. Hungary has earned an outstanding international reputation in this field, in which even relatively modest telescopes can produce world-class scientific results. At the same time, a strong school of supernova research has developed in Szeged. We study stellar systems, some of which will eventually explode as supernovae, while our colleagues investigate those that have already exploded. We brought these two areas together in our proposal for the HUN-REN research group grant.
Q: What kind of equipment do you have at your disposal?
A: Our flagship instrument is one of the largest telescopes in Hungary, with a primary mirror measuring 80 centimeters in diameter. Only three telescopes of this size operate in the country – one here in Baja, one in Szombathely, and one at Piszkéstető in the Mátra Mountains. Hungary has only two larger telescopes, both located at Piszkéstető. In addition, we operate two smaller telescopes that also play an important role in our research and educational activities.
Q: You contributed to the discovery of a 3+1 hierarchical stellar system using data from the TESS space telescope. How did you gain access to those observations? Is it possible to ‘buy telescope time’?
A: Data from most space telescopes are publicly available. Here at the Baja Observatory, we use our own telescopes only for follow-up observations. When people hear the term space telescope, they usually think of the Hubble Space Telescope or, more recently, the James Webb Space Telescope. These produce breathtaking images, but their real scientific value lies in the data behind those images rather than in their visual appeal. Alongside them, however, there are many smaller, highly specialized observatories, including space-based missions such as the Transiting Exoplanet Survey Satellite, or TESS. Although the TESS telescope is much smaller, the absence of Earth’s atmosphere allows it to make exceptionally precise measurements. Its main challenge is simply to avoid pointing directly at the Sun or the Moon, whose intense light would overwhelm its detectors. TESS was designed to search for exoplanets. It is still surveying the sky as we speak, and its data are freely available online. In practice, all you need to access them is a good internet connection.
Dr. Tamás Borkovits, astronomer. Photo: Karina Bartha
Q: How did you uncover this remarkable stellar system? And what makes it so extraordinary?
A: Astronomy is an inherently international discipline, and we collaborate closely with colleagues around the world, including researchers at the Massachusetts Institute of Technology (MIT) and NASA. Through these collaborations, I became involved in projects using data from TESS and, before that, the Kepler Space Telescope. Both missions were designed to search for transiting exoplanets, and TESS continues that search today. Their observations, however, also revealed eclipsing binary stars, some of which exhibited behavior that raised questions almost no one but me was investigating at the time. That is why my colleagues reached out to me.
The eclipsing binary stars we study are, in essence, doing the same thing as transiting exoplanets. Most planets beyond our Solar System – or exoplanets – are discovered when, as seen from Earth, they pass in front of their host star and block a small fraction of its light, causing the star to dim. If this happens periodically, it usually indicates the presence of an exoplanet. An eclipsing binary, by contrast, consists of two stars orbiting so close together that even the largest telescopes cannot resolve them as separate objects. When, from Earth’s perspective, one star passes in front of the other, followed later by the reverse, their combined brightness decreases far more than when a relatively small planet crosses a much larger star. That is one reason eclipsing binaries were studied long before transiting exoplanets. Some eclipsing binaries produce such pronounced changes in brightness that they can even be detected with the naked eye, dimming every day or two. TESS observes vast numbers of these systems as well. The questions that interested us, however, did not arise from one of these more classical cases.
We first discovered such systems using the Kepler Space Telescope: eclipsing binaries orbited by a more distant third star. For reasons of dynamical stability, the third star must orbit much farther from the inner pair, making it more difficult to detect. To observe its eclipses, the outer orbital plane must be aligned almost exactly with our line of sight. Kepler discovered the first such system in 2011. It dimmed every 15 to 20 days for one or two days, with each event looking slightly different because the three stars were in a different configuration each time an eclipse occurred. These triple systems are rare. Among the hundreds of millions of stars observed by Kepler, around 2,500 were eclipsing binaries, and only 12 or 13 showed these extra eclipses.
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| The Baja Astronomical Observatory. Photo gallery: Karina Bartha |
The Baja Astronomical Observatory. Photo gallery: Karina Bartha
There is, however, another way to detect a third star. Its gravity causes the other two stars, as they orbit each other, to move alternately slightly closer to us and then slightly farther away. Because light travels at a finite speed, the light from such a system reaches Earth slightly earlier at some times and slightly later at others. When the two stars are closer to us, the eclipse is observed a little sooner; when they are farther away, it occurs slightly later. Instead of taking place at perfectly regular intervals, the eclipses shift back and forth in a periodic pattern. This phenomenon is known as the light-travel time effect (LTTE).
If the third star is close enough to the binary, its gravity also perturbs the motion of the two inner stars – and vice versa – so they no longer orbit each other in a perfectly regular way. At that point, predicting the timing of the eclipses is no longer straightforward. I never imagined that we would actually observe such a system. Back then, I worked out the eclipse-timing variations caused by these gravitational perturbations more or less for the desk drawer, simply because I needed one more publication for my PhD.
Then, ten years later, the Kepler Space Telescope detected several such systems, and researchers in the United States contacted me because I was the only person who had published equations describing these effects. Studying these systems – especially gravitational perturbations and third-body eclipses – required an entirely new type of light-curve modelling software, quite different from that used for ordinary eclipsing binaries.
TESS was launched in 2018, and within two years it had observed around a billion stars. By now, it has identified more than a hundred triply eclipsing systems. At first, we thought the record-setting 3+1 hierarchical stellar system I mentioned was simply a fairly compact triply eclipsing system. The third star orbits the close binary every 51 to 52 days – not a record in itself, but interesting enough for us to continue monitoring it.
That was when we discovered what made the system truly exceptional: there was a fourth star. Every 51 days, we observed two extra eclipses. But those eclipses also occurred slightly earlier or later than expected, and the only way to model the observations successfully was to introduce a fourth star orbiting even farther away and perturbing the entire system.
We were fortunate that the system is relatively bright. Although it is 200 to 300 times fainter than the faintest star visible to the naked eye, that is not particularly faint for modern telescopes. This allowed us to carry out spectroscopic observations by dispersing the starlight and recording its spectral lines. An American colleague performed these observations using an instrument designed by Gábor Fűrész, an SZTE alumnus who had already designed a spectrograph for his undergraduate thesis. A more advanced version of that instrument is now operating in Arizona.
We found that the fourth star completes an orbit in only about 1,040 days. Of the four stars in the system, three are considerably larger, brighter, and hotter than our Sun, while the fourth is roughly the same size as the Sun.
To sum it up: two stars orbit each other every three days in a very tight configuration, while a third circles the inner pair every 51 days. If we placed these three stars in our Solar System, all of them would fit well within Mercury’s orbit. A fourth star, roughly comparable to our Sun, orbits the inner triple every 1,046 days, giving the system its hierarchical structure. For reasons of dynamical stability, the orbital periods differ greatly, reflecting the different sizes of the orbits. Even if we placed the entire four-star system in our Solar System, the fourth star would still orbit between Mars and Jupiter.
The triply eclipsing triple itself is fairly compact, though far from the most compact known. In fact, we also discovered the most compact triple-star system identified to date using TESS data. Moreover, one of our colleagues, Dr. Tibor Mitnyan – my postdoctoral researcher in Szeged – has found another record-breaking triple system. We expect to publish the findings soon.
The discovery we are discussing is truly unique because of the presence of the fourth star and the system’s extraordinary compactness. Among all known hierarchical 3+1 stellar systems, it has by far the shortest outer orbital period, the smallest overall size, and the most compact configuration ever identified.
Q: Is a system like this genuinely rare, or is it simply very difficult to detect?
A: In reality, both. Hierarchical triple and quadruple star systems are probably uncommon to begin with – especially when they are as compact as this one – because they require very specific conditions to form. At the same time, they are extraordinarily difficult to detect. From Earth’s perspective, the orbital planes of all the stars must be aligned almost perfectly edge-on for them to eclipse one another. Timing also matters. Compared with the billions of years that stars can exist, a human lifetime is only a brief moment. Finding a quadruple system of this kind ultimately comes down to sheer luck. In this case, too, a whole series of fortunate coincidences played a part.
Q: Could discoveries like this one eventually have practical significance here on Earth?
A: I cannot give a precise answer to that. When the Italian physician Luigi Galvani noticed a frog’s leg twitching after he touched it with an iron rod, laying the foundations for the study of electricity, or when James Clerk Maxwell formulated the laws of electromagnetism, who could have imagined that these discoveries would one day lead to television, radio, or the internet? The kind of basic research we do has no obvious or immediate practical application. Its value also lies elsewhere: curiosity and intellectual challenge are part of what makes us human. Whether this particular discovery will one day have an impact, I simply cannot say – perhaps that will only become clear centuries from now. Unfortunately, there is a growing tendency to expect every field of research to deliver immediate practical applications. I do not believe that is something we should force.
Photo: Karina Bartha
Q: What does making a discovery of this magnitude mean to you personally? What continues to motivate your research?
A: In some ways, our work is a bit like the television series CSI: NY. The investigators reconstruct what happened from the tiniest clues – and, in a sense, so do we. A space telescope observes a particular region of the sky for only a limited time, but returns to it from time to time. That is enough for us to recognize that something unusual is happening. Then we begin to follow it. If a star is visible only from the Southern Hemisphere, we rely on colleagues there to continue the observations. From just a few short observing windows, we try to piece together what is happening and why. That is what makes the work so exciting.
We have even modelled the future evolution of this 3+1 stellar system. Within a few hundred million years, the three inner stars will collide and merge. Of course, we will never witness it, but it is immensely satisfying to know that I can model such a system. In practical terms, only a handful of people in the world understand what is happening here – not only qualitatively, but also quantitatively, in terms of precise values and stellar masses.
Curiosity is one of the greatest driving forces in science. I see a phenomenon, and I cannot rest until I understand it.
Q: How do you decide which phenomena to investigate? Do you set out to look for specific types of systems, or do unexpected discoveries often guide your research?
A: A space telescope observes hundreds of millions of stars and produces light curves for one to two million of them every month. These data contain countless unusual phenomena – far more than we could ever investigate – so our main focus is on searching for extra eclipses. We also benefit from the work of highly dedicated amateur astronomers – so-called citizen scientists, most of them from the United States – who examine astronomical data available online. Many are retirees, as this kind of work takes time. They are incredibly experienced and, in some cases, outperform any algorithm. When they spot something interesting in a light curve, they let us professionals know.
Photo: Karina Bartha
Q: Alongside astronomy, you also have a deep interest in spirituality. How do the two coexist in your worldview?
A: It is true that I have studied Eastern metaphysics extensively, practice yoga, and once had a teacher in India. At heart, I consider myself a spiritual person, but I also pursue astronomy very seriously. I have to admit that I do not fully reconcile every aspect of my own life. I see that as a reflection of my own human limitations rather than any shortcoming of spirituality.
To me, the material world is only a small part of a much broader spiritual reality, although the study of nature can also take us a very long way. I do not believe there is any real conflict between science and spirituality. In Newton’s time, when the natural sciences were beginning to take shape, scholars studied what they understood to be divine work manifested in nature. They were far from denying the existence of God.
Since the Enlightenment, particularly in the Western world, the natural sciences and spirituality – primarily Christianity – have been set against one another. A century ago, many scientists took pride in being atheists, believing they had no need for God to explain the world. Yet when we begin to ask how the Universe came into being or how human existence began, we soon encounter questions that natural scientists often simply pass over.
I am not saying this as a natural scientist, but I am convinced that nothing could have come into existence entirely spontaneously. How could the laws of nature have existed before particles themselves existed? It is almost as if something had to intervene from outside the system at the very beginning; after that, of course, the system could continue to function on its own, according to its own order, without further intervention.
Original Hungarian article by Helga Balog
Photos: Karina Bartha
