Story

Vol.06

The challenge of exploring the origin of the universe
―Expanding the vision of the universe at the Pioneering Research Institute―

Chief scientists Sakai, Suzuki, Tamagawa, and Nagataki are pioneering the frontiers of space science at the Pioneering Research Institute. They discussed on extreme environment physics, and Earth and planetary life science, high-energy astrophysics, and star and planet formation research, reaffirming that the Pioneering Research Institute’s free interdisciplinary exchange and research environment provides fertile ground for generating new ideas, technological developments, and breakthroughs that may completely transform our view of the universe and life.

Approaches to studying the universe

　───First, please tell us about the research you are each involved in.

　Nagataki: I conduct theoretical research on the large explosions (supernova) that occur at the end of lives of massive stars, and on gamma-ray bursts, which are said to be the most gigantic explosions in the universe. We use computer simulations in an attempt to reproduce these explosions and solve a fundamental cosmic mystery: “How do stellar explosions occur?” Regarding SN 1987A, a typical supernova, we made a theoretical prediction that the explosion was not spherically symmetric, but rather shaped like a rugby ball, with slightly uneven intensity between the upper and lower regions. Our theoretical prediction was unique, and there was considerable skepticism toward our theoretical conclusions. However, in recent years, several observational results supporting our theoretical predictions have been reported, which we find very encouraging. That said, this doesn’t mean that our theory has been completely proven. Further theoretical research, as well as supporting observations and analyses, are needed.

　Suzuki: My research is on the metabolism and ecology of microorganisms living in the Earth’s subterranean biosphere. The Earth is a part of the universe. Understanding how life can exist in an environment of rock, water, and air is important for considering the universality of life. Although life has not yet been found outside the Earth, extremely unique metabolic mechanisms exist in subterranean environments, such as microorganisms that depend on hydrogen produced by reactions between rocks and water and those that capture external electrons using the electrical properties of rocks.
　I conduct multifaceted investigations to find out how these microorganisms convert the energy contained in rocks and water into the energy of life. I believe that the insights gained from this research will lead to an understanding of how life emerged and evolved on the early Earth, which may also contribute to the development of astrobiology (a study exploring the potential life in space).

　Tamagawa: I am conducting research to elucidate extreme physical phenomena occurring in celestial bodies by observing the universe using high-energy electromagnetic waves, such as X-rays and gamma rays. One of our major research themes is to clarify observationally where, through what processes, and in what quantities the elements in the universe were produced. Most elements heavier than iron are thought to be produced during dramatic astronomical phenomena, such as supernova explosions and the merger of neutron stars. We seek to directly observe the site where such elements are created through satellite-based X-ray and gamma-ray observations. Furthermore, if a neutrino observatory detects any signs of an explosion, hopefully we can immediately point an X-ray observation satellite, such as XRISM, in that direction to make detailed follow-up observations of the early stages of the explosion.
　In the future, we will seek to establish observational technology that enables the direct detection of gamma rays emitted during the decay of unstable atomic nuclei and the in situ confirmation of the elements that are synthesized there. Through these efforts, we aim to obtain a comprehensive picture of nucleosynthesis in the universe through observations.

　Sakai: My research aims to clarify the process of planetary system formation, including its chemical environment. Specifically, it involves how elements produced in stars and dispersed into space, which Dr. Tamagawa is exploring, subsequently form molecules, then solid particles (dust), and become the origin of rocky planets to ultimately constitute planetary systems like our solar system. A comprehensive understanding of the physical and chemical evolution of star and planet formation is essential.
　To address this question, we use state-of-the-art observational instruments, such as the JWST and ALMA to investigate in detail the properties of molecules and solid materials, including dust grains and icy mantles, in regions where stars and planetary systems form. However, accurately interpreting the observed spectra requires comprehensive spectroscopic reference data , a kind of “dictionary of the spectral fingerprints of individual species derived from laboratory spectroscopy”, and such data are still severely lacking.
　To address this challenge, we are also developing molecular spectroscopy instruments and performing precise laboratory measurements of spectral lines to provide the fundamental reference data required for astronomical observations. Observational data, however, represent only snapshots in time. Therefore, it is equally important to use simulations that combine star and planet formation models with chemical reaction network calculations to understand how these systems evolve over time. Such theoretical approaches also require key physicochemical parameters, including the rate coefficients and branching ratios of individual chemical reactions, as well as the evaporation temperature of molecules. Addressing this requires close collaboration with experts in quantum chemistry, laboratory reaction experiments, and surface science, playing a bridging role that connects observations, experiments, and theory.

Inspiration born from heterogeneous connections

　───Please tell us about the research environment unique to the Pioneering Research Institute and any experiences you have in relationships with fellow scientists.

　Tamagawa: The Pioneering Research Institute brings together experts in a wide range of fields, and I feel the breadth of coverage every day. Scientists with different backgrounds often come together in the same place for discussions, which inspires new ideas in everyday meetings or casual conversations. I have seen many instances where such serendipitous interactions have led to new research developments.
　RIKEN has multiple research centers, in each of which scientists are likely working on relatively similar themes. The Pioneering Research Institute, however, deliberately recruited scientists with different specialties to work in the same group, creating a highly interdisciplinary environment. This makes it easier to engage in cross-disciplinary discussions, fostering new perspectives and new possibilities for collaboration that are not bound by conventional thinking. I believe this represents a major feature of the Pioneering Research Institute.

　Sakai: That’s right. For example, when we once needed to carry out spectroscopic measurements of a rather unusual molecule, I wasn’t sure how I could obtain it for the analysis. As it happened, an organic chemist was working in the neighboring laboratory. When I asked for advice, he kindly explained not only where such molecules could be purchased but also how they could be synthesized. On another occasion, he even said, “Let me ask my previous mentor about this,” and consulted a leading figure in organic chemistry. I was also able to use part of their equipment. These are the kinds of questions one might normally hesitate to ask, but here there is a very open atmosphere where it feels natural to seek advice. There’s a very open atmosphere where it feels easy to ask questions, even ones I might normally hesitate to raise. In fact, the Chief scientists themselves often show genuine interest and ask questions such as “What are you planning to use that molecule for?” Conversations like this frequently grow into broader discussions. I feel that one of the distinctive strengths of the Pioneering Research Institute is this culture in which people genuinely enjoy exciting ideas, whether they are asking questions or being asked.
　The very fact that the four of us are able to sit together like this and exchange ideas is, in itself, a good example of that. Researchers in the biological scientists, such as Dr. Suzuki, are not people I would normally interact with on a daily basis. Yet whenever I speak with her, I find her perspectives extremely interesting. The conversations naturally lead to opportunities to ask each other questions and deepen our understanding, and everyone is eager to engage. Being in such an environment is something I truly appreciate.

　Suzuki: I remember the conversation I had with Dr. Sakai that made a lasting impression on me. She said, “If the microorganism is about 100 nanometers in size, perhaps we can observe all their elements.” That kind of thinking had never occurred in biology. Because microorganisms are living organisms, we tend to focus on analyzing them at the genetic level. But she said, “At that size, it seems possible to analyze them on an elemental level and identify all the elements, right?” I was surprised at such a fresh idea.
　To understand the origin and evolution of life through the study of subterranean microorganisms, it is essential to clarify the relationship between matter and life. Progress of science is driven by the understanding of how the evolution of matter and the evolution of life are linked. I believe that the core of our research is to explore processes through which molecules are created, then more complex molecules and structures, and finally living bodies and components formed from them.

　Sakai: In space, the conditions rarely settle into equilibrium. Due to constantly changing temperatures and densities, chemical reactions do not proceed uniformly, leading to the composition of molecules and materials varying from place to place with inherently different gradients. For astrochemists like me, this is, in a sense, the normal state of affairs. Precisely because systems remain far from equilibrium, abrupt physical and chemical transitions can occur, and sharp interfaces often emerge between regions with very different physical conditions.. These phenomena are, in many ways, signature of nonequilibrium processes.

　Suzuki: We can say that living organisms cleverly make use of nonequilibrium environments similar to those found in space, in order to extract energy. Living organisms today convert and consume the energy obtained from their environment into a molecule called adenosine triphosphate (ATP). They luckily have acquired such a mechanism. I believe that the evolution of matter, in which matter evolves through repeated reactions in its environment, and the evolution of life, in which living organisms evolve by acquiring mechanisms for utilizing energy, are essentially very similar processes. In terms of energy flow, it is obvious that the two evolutions are linked.

Interdisciplinary research program and specific joint research

　───What kind of joint research are you currently working on?

　Sakai: In collaboration with Yousoo Kim, the chief scientist at the Surface and Interface Science Laboratory, we carried out experiments in which individual atoms or molecules are placed on surfaces that mimic interstellar dust grains and energy is supplied from a probe to investigate how they diffuse, react, desorb, or evaporate from the surface. These processes closely resemble the reactions that occur on the surface of interstellar dust and provide valuable insights for understanding the chemical evolution of the universe.
　We are also collaborating with scientists at the Astro-Glaciology Laboratory (Director: Yuko Motizuki) at the Nishina Center for Accelerator-Based Science to perform reaction experiments on ice surfaces. Ice surface reactions are critically important in astrochemistry, particularly for the formation of interstellar organic molecules. Studying these processes is essential for understanding the molecular evolution of the universe.

　Tamagawa: Our laboratory also conducts research on space utilization. X-rays emitted in space are absorbed by the Earth’s atmosphere and cannot be observed on the ground. For this reason, X-ray telescopes must be placed in space. We conduct research on such space utilization technologies and the framework for space observations. For this research, we are working in collaboration with various scientists at RIKEN, not just researchers at the Pioneering Research Institute, to discuss and pursue joint research on how to realize the technologies necessary for scientific observations in space.
　We would like to have more opportunities to collaborate with scientists fascinated by possible outcomes of scientific research in space (with a space theme), like you, Dr. Suzuki, expert at research on microorganisms in the subterranean biosphere.

　Suzuki: I participate in many joint research projects in biology. For example, I am collaborating with Shintaro Iwasaki, the chief scientist at the RNA Systems Biochemistry Laboratory, on the precise analysis of RNA and molecular-level reactions. Current research focuses on macroscopic studies, such as the behavior of life as a whole and biological systems, but ultimately, I want to understand them in detail, right down to the constituent level. By collaborating with Dr. Iwasaki, who has deep expertise in RNA, we’re making progress in analyzing biological phenomena at high resolution.

　Tamagawa: We normally observe materials on distant celestial bodies with remote sensing, using various electromagnetic waves. However, another approach is to dispatch sensors to planets or asteroids and make direct measurements there. Dr. Suzuki’s laboratory has extremely high-precision measurement technology. We began a joint research program with the idea that this technology, developed on the ground, could be applied to space missions. In order to install sensors on human-made satellites or probes and operate them in space, we need compactification of sensor systems. If it succeeds, I believe it would hugely benefit not only space observations but also analyses on the ground. For example, scientists would be able to carry compact instruments with them to conduct material analysis on site in a wide range of environments.

　Nagataki: Within the Pioneering Research Institute, we often collaborate with Dr. Tamagawa’s laboratory. Even if I am absent, members of our lab team sometimes work together with scientists in Dr. Tamagawa’s laboratory.

　Tamagawa: We conduct joint research in an unconstrained manner. Even when I’m not co-author of a paper, Dr. Nagataki works with scientists in my laboratory, or even when he is not involved, we work with scientists in his laboratory.

　Nagataki: As for neutron research, we work on the expression of properties unique to neutron stars together with scientists in the Nonequilibrium Quantum Statistical Mechanics RIKEN Hakubi Research Team (matter research/nonequilibrium physics). We have actively interacted with those scientists through regular study meetings and joint paper writing. Thanks to a joint research project emerged from such interaction, I had an opportunity to be an author of my first paper on condensed matter physics.
　Furthermore, the RIKEN Pioneering Projects was launched in 2013. The first program adopted in the project was iTHES in which many members of Ils (Chief Scientist Laboratories), predecessor of the Pioneering Research Institute, participated. iTHES has now been succeeded by the RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS). iTHEMS is a theoretical research group, but represents an initiative to gather scientists from a wide range of fields, including astronomy, atomic nuclei, material science, and life science, for working in close relationships under one roof. It has an atmosphere of positive interdisciplinary exchange enabled by shared themes of interest and common mathematical knowledges.
　To give a recent example, inspired by a leading scientist in Dr. Tamagawa’s laboratory, we launched joint research on a method to detect sudden astronomical phenomena, such as supernovae, based on observational data. We investigated the method using quantum machine learning techniques, which scientists in iTHEMS are also working on. This resulted in the publication of a fairly ambitious paper.

A shared focus on the evolution of matter and a culture of free thinking

　───What kind of results have you produced in such a free environment?

　Tamagawa: For example, Dr. Sakai, Dr. Nagataki, and I worked together on the RIKEN Pioneering Research Project “Evolution of Matter in the Universe (r-EMU).” At that time, Dr. Suzuki had not yet joined RIKEN, but the project addressed themes that connect physics and atomic nuclei to chemistry, and we hoped that, in the future, it could also incorporate the perspectives from the biological sciences. The project aimed to view the large flow from atomic nuclei to life as one continuous stream of science.

　Sakai: When we look at the evolution of matter, from elementary particles and atomic nuclei to atoms and molecules, and ultimately to prebiotic molecules at the boundary between chemistry and biology, we find that everything forms a hierarchical structure. Although each stage may appear to belong to a different research field, they are essentially part of a single continuous chain.

　Nagataki: The r-EMU was an incredibly stimulating initiative. Contrary to theoretical frameworks like iTHEMS, the r-EMU provided an environment that allowed us to engage in daily discussions with experimental scientists, which was a valuable learning opportunity for me. Although r-EMU activities ended after five years, the relationships fostered there continue to this day. Among the research projects, especially those focusing on collaboration, the most impressive one was an attempt to theoretically explain how molecules were formed in the bipolar explosion in the supernova SN 1987A. Laboratory scientists played a leading role in establishing a numerical simulation incorporating highly complex reaction rates to identify reaction pathways through which molecules, such as CO and SiO, were formed. The result was a belt-shaped distribution of CO, reflecting the asymmetry of the explosion. Around the same time, ALMA telescope observations suggested a ring-shaped CO structure. I was surprised to find that our model reproduced this characteristic. That was a moment when I realized how much observations could align with a theory.

　Suzuki: I am currently working on a planetary life science project from the perspective of how CO can contribute to the formation of polymers, which are building blocks of life. In addition, from the perspective of life itself, I believe that the CO molecule plays a very important role in generating precursors to polymeric substances. Recently, I have come to feel a strong connection with the research results of Dr. Nagataki and Dr. Sakai.

　Sakai: From the perspective of molecular evolution, CO molecules adsorb onto the surfaces of interstellar dust, where reactions lead to formation of molecules such as methanol. These molecules can react with one another to form larger organic molecules. Because the timescale of these reactions can be constrained, CO serves as a particularly “clean” reference molecule in astrochemistry.

　Suzuki: In our field of life science, we are also exploring what kind of diverse substances are produced from CO and how such process resembles chemical reactions of life. My major theme is exploring how lifeless chemical reactions lead to biocatalysis processes emerged later in living organisms. Listening to your stories today, I feel that the connection between the evolution of matter and the evolution of life is becoming stronger in my mind.

Open environment and interaction take research to the next stage

　───Please tell us once again about attractive points of the Pioneering Research Institute.

　Tamagawa: I believe that among many organizations within RIKEN, the Pioneering Research Institute provides the best environment for scientists who want to deepen their research from their own unique perspectives. You can not only pursue your own themes to your heart’s content but also, thanks to daily discussions and interactions, you may see your themes expand in a direction you never imagined before. I feel that the Pioneering Research Institute is a place filled with such possibilities.

　Nagataki: The Pioneering Research Institute is an organization that values freedom above all else. Scientists can continue to pursue their dreams or advance their research in new directions through interactions with those around them. The choice of which path to take is up to each scientist. We are colleagues respecting each other’s will and ambition. That’s the atmosphere we have here. Looking around, you will find many scientists who are willing to help you. Some have specialties similar to yours, while others are experts in completely different fields. Because they are all highly skilled professionals, I’m sure this is a truly reliable environment if you want to pursue the research you have cherished.

　Suzuki: I believe that if young scientists with an open mind seriously tackle their themes for a few years, some kind of breakthrough is sure to occur. RIKEN is truly the best environment for this.
　As you work on your research, there will be times when you feel skeptical and wonder, “Is my perspective valid?” But even at such times, there is always someone to talk to. Just ask him or her , “What do you think from the perspective of physics or chemistry?” Discussions from completely different perspectives will make you aware of different visions of the same phenomenon. You can think freely based on your own curiosity, talk to a variety of scientists, and generate breakthroughs. I think accumulation of such efforts will shape research that leads to the future.

　Sakai: Rather than having a particular institutional “framework”, what makes the Pioneering Research Institute special is that there are always people who are willing to work with you to figure out how to pursue your ideas. In that sense, I believe this is its real strength. You can naturally engage in discussions not only with researchers in closely related fields but also with those from quite different disciplines. There is no need to formally arrange a collaboration, new ideas often emerge simply from casual conversations, for example when you happen to meet someone in the cafeteria. This is a place where collaborations naturally arise in daily interactions.

Truth of the universe... and towards the possibility of life

　───How do you think your research will develop over the next 10 to 20 years? And what kind of research do you want to pursue in the future?

　Nagataki: I think the landscape 10 years from now will be slightly different from the one 20 years from now. In 10 years, gravitational wave astronomy, particularly multi-messenger astronomy centered on gravitational waves, will make great advances, further expanding the scope of the universe that can be captured by gravitational waves. Certain phenomena, such as how the merger of neutron stars and black holes emits light (or not), should be more systematically understood.
　Furthermore, given a vast amount of accumulated data, including galaxy observations, and advances in AI technology, we will be hopefully able to paint a more detailed picture of the universe based on statistical evidence. Decreasing density of dark energy over time may definitely cause expansion of the universe to slow down, which will help us further deepen our understanding of the universe.
　In 20 years, I’m very intrigued by outcome of the mission to find definitive evidence of the inflationary period, which is believed to have occurred immediately after the birth of the universe. Furthermore, if quantum computers have made great advances, we may be able to perform calculations that are not feasible with the current classical computers, potentially bringing about major breakthroughs in theoretical research. Personally, I strongly hope that the day will come when supernova explosions are observed once again in the Milky Way, allowing us to compare our theoretical models in detail with observations of gravitational waves, neutrinos, and electromagnetic waves, such as X-rays.

　Tamagawa: While some space observations can only be conducted using large satellites, I believe that the use of small satellites will rapidly expand. Our laboratory aims to launch multiple small satellites to continuously monitor the universe, combining results obtained with high-sensitivity observations by large satellites, thereby creating a new observation system. Thanks to growing space development activities driven by private companies, now it’s possible to promptly deploy small instruments into space. This change is greatly expanding the scope of space utilization overall.
　There are some areas of basic science not fully connected to the space environment. Linking extreme environments, such as zero gravity and intense radiation, to basic science will pave the way for new fields of research.
　At the Pioneering Research Institute, seeds of research in diverse fields are sown through daily discussions. By utilizing these seeds, we hope to propose a continuous monitoring system using a small satellite network and create a new way to observe space.

　Sakai: Given the dramatic growth of observational data, we are entering an era in which AI technologies are increasingly used to extract information from these vast datasets. Against this backdrop, I believe the more important question is how reliable the data themselves are that AI is analyzing. Only scientists who understand both observational data and theoretical calculations can make this judgment. While technology to send observational instruments into space is certainly important, the ability to interpret the data correctly is just as crucial. For this reason, I believe the field will move toward developing internationally shared databases through global collaboration.
　In my own research, for example, there is a severe shortage of the “dictionaries” needed to identify molecules (i.e., molecular spectral data). To maintain global leadership in astronomical observations, it is essential to continuously refine, maintain, and update these foundational datasets.

　Suzuki: It’s not easy to say with certainty that we will find living organisms in space. However, I believe one of our ultimate goals is to find a planet that supports life. Previously, there were only two options: life does exist or not. Thanks to the improvement in observational technology, we are gradually looking into details between the two options at a higher resolution. For example, we will be able to see even a very fine sign of life, such as a formation of functional molecules like enzymes.
　There may exist completely different types of life that rely on something other than well-known DNA, RNA, and proteins. Exploring possibilities in the environment of space completely different on Earth may reveal an unimaginable picture of life .
　My research deals with large-scale themes, such as life as a whole and biological systems, but ultimately, I hope to meticulously break down each of constituents and understand them at a high resolution.

　There is little doubt that bringing together insight from different fields will deepen our understanding of the structure of the universe and the origin of life. The challenge of exploring the universe will continue to inspire researchers in the years ahead.