Departmental Overviews (Astronomy): Where Tradition and Innovation Meet ― Challenging the Unexplored Mysteries of the Universe

-The Department of Astronomy-

Professor Motohide Tamura (Head of the Department of Astronomy)

Preface

About 30 years ago, I lived in America for four and a half years. At the time, reruns of the original Star Trek series were airing on television and in every episode the narrator would say the following classic lines: “Space: the final frontier. These are the voyages of the starship Enterprise. Its five-year mission: to explore strange new worlds. To seek out new life and new civilizations. To boldly go where no man has gone before!”¹

When I heard these words, especially at times when I was exhausted from conducting observations, running experiments and analyzing data, I would be reminded anew of the allure of the universe.

Of course, this show is science fiction set in space and the frontiers of science are not limited to the universe. However, the universe is indeed filled with mysteries and humankind’s desire to challenge the unknown, which has existed since long ago, will likely not change in the future. Astronomers are fascinated by space and like Galileo when he wrote about the first observations of the universe through a telescope in Sidereal Message, they want to share their discoveries with the public. Here in the Department of Astronomy, our members also work to approach these mysteries in an attempt to solve them.

¹Star Trek is a story about the starship U.S.S. Enterprise, which is on a five-year mission to explore the universe, last remaining frontier for humankind where new life that has never been imagined by mankind awaits. (Reference: Star Trek Universe page)

Departmental Overview

The Department of Astronomy at the University of Tokyo (which was founded in 1878 as the Department of Astrology) is said to go all the way back to the Edo Period (around 1684). In present day, when looking from the Main Gate of the University of Tokyo, the Department of Astronomy can be found right behind Yasuda Auditorium on the 10th and 11th floors of the School of Science Building 1.

Our Department has 11 faculty members, which is small for the School of Science; however, we play a central role in astronomy education and research at the University of Tokyo through our collaborations with over 20 faculty members from the Institute of Astronomy (located in Mitaka), Research Center for the Early Universe, Graduate School of Arts and Sciences, Institute for Cosmic Ray Research, as well as the National Astronomical Observatory of Japan and Institute of Space and Astronautical Science.

As our Department only admits 10 undergraduate students every year, students enjoy a tight-knit atmosphere that makes them feel at home. The Graduate School accepts about 23 students into the Master’s program each year while more than 10 students acquire Doctoral degrees. Within the few undergraduate departments at Japanese universities that specialize in astronomy education, our Department is considered to be of the highest standard both domestically and internationally due to our collaboration with numerous faculty members at various institutions and our numerous research themes. Furthermore, through our cooperation with the National Astronomical Observatory of Japan and Astrobiology Center, we provide an environment where students are able to readily obtain training in developing astronomical instruments, observation, data analysis, and so forth.

Education and Career Paths

Astronomy is based on physics and mathematics, which is why our initial lectures emphasize both. From the latter half of second year, students concurrently attend lectures that provide them with a basic foundation in astronomy. In their third year, students gain experience in not only observational training using visible light or radio telescopes but also in experimentation and data analysis.

Students conduct research in their fourth year, which allows them to experience cutting-edge research first-hand by working with a supervisor who provides them with one-on-one training in areas such as observations, analysis, and simulation. Those continuing on to graduate school may be able to publish their research results in an academic journal. There are also support systems in place for undergraduate students who are interested in studying abroad. Furthermore, all students are required to take a course on research ethnics in their third or fourth year.

In the Graduate Department of Astronomy, students are able to advance their research by utilizing telescopes in both Japan and overseas and spending extensive time abroad. We have many students who use data obtained from the Subaru Telescope in Hawaii or the ALMA Telescope in Chile for their Master’s theses or Doctoral dissertations. Additionally, some students not only use the Subaru Telescope for observations but are also in engaged in developing observational instruments (Figure 1). Furthermore, the TAO Telescope, which is currently under construction in Chile by the Institute of Astronomy, is scheduled to have its first light in 2019 and will become an invaluable telescope for educating our graduate students and conducting world-class research.

On average, over 80% of our undergraduate student advance to graduate school with their sights set on becoming researchers. However, career paths have been broadening recently, which means that students have more diverse career options, ranging from fields related to computing and optics to government agencies and finance.

Figure 1. IRD is an infrared spectrograph that was developed for the Subaru telescope in order to find Earth-like exoplanets. ① Light from astronomical bodies is collected at the telescope’s Nasmyth focus and then injected into the spectrometer system through optical fibers. ② It then passes through the mode scrambler, which reduces light disturbance. ③ The light from the laser frequency comb, which becomes the wavelength standard, also enters the spectrometer system by the same route as the light from astronomical bodies. （© Astrobiology Center, The University of Tokyo）

Research

Astronomy is a discipline with one of the longest histories alongside that of medicine, and like the multitude of mysteries in the universe, a variety of fields have been established over its history. Similar to other scientific disciplines, astronomy has trends in each field; however, there is no excitement in simply following a current trend. The Department of Astronomy has adopted a faculty system that covers as many diverse fields as possible and has become a world leader in research on topics such as distant galaxies, high energy phenomena, supernovae, interstellar matter and chemistry, asteroseismology, and exoplanets. The aforementioned fields are listed in descending order according to their scale of research as our Department does not rank nor promote one particular field in astronomy. Furthermore, although there is a so-called distinction between observation and theory, our Department places an equal emphasis on both, which allows us to meet students’ wide range of interests. Below are a few examples of research findings from our Department. If you’re interested in any of this research or would like to find out more, please visit our homepage where you can browse through the laboratory pages of our faculty members.

There are hundreds of billions of stars within a galaxy and within the infinite number of galaxies that exist in the universe, we live in one: the Milky Way. A supermassive black hole lies at the center of our galaxy, which has a beautiful connection with the mass of the galaxy despite the ten-digit difference in scale. There is also a mysterious substance known as dark matter, which surrounds the galaxy in huge quantities and cannot be seen by light. On the other hand, galaxies in the present universe are not uniformly distributed and form a massive network known as the large-scale structure of the universe. When looking at the universe from the most macro-perspective, a galaxy is considered to be the smallest unit that contains knowledge about the history and structure of the universe.

As shown in Figure 2, Galactic Astronomy is a field of study that examines the space and time of a large part of the universe. Professor Kashikawa’s research group investigates the formation and evolution of galaxies over the 13.8 million year history of the universe and aims to understand how galaxies took on their present form. In particular, his group focuses on the observation of distant galaxies, which reveal the state of the early universe. By gathering as many photons as possible that have travelled for 13 billion years through the universe, they aim to unravel how galaxies formed and the reionization of the universe.

Figure 2. A conceptual diagram of the history of the universe, from its birth 13.8 billion years ago after the Big Bang (left) to the present day (right).

More precise observations in recent years have shed light on how dark energy, which is accelerating the expansion of the universe, is a main component of the universe. The true nature of dark energy is one of the biggest mysteries in modern cosmology and various astronomical observations are being conducted in order to approach it. One of these is the FastSound Project, which is led by Professor Totani. Using the Subaru Telescope, they created an innovative 3D map of the universe at around 4.7 billion years after its birth, the furthest distance in history (Figure 3). Furthermore, phenomena such as supernovae or gamma ray bursts, which is caused by the massive explosion of a star, is not only a fascinating research topic but also a tool to explore the distant universe. The Graduate Department of Astronomy investigates these kinds of phenomenon by using computer simulation to derive information about the physical state of the early universe from these observational data. The discovery of mysterious astronomical objects is another appealing aspect of this field. For instance, a mysterious phenomenon known as fast radio bursts was discovered several years ago yet to this day remain a complete mystery, perplexing astronomers around the world.

Figure 3. The FastSound Project’s illustration of the large-scale structure of the universe around 4.7 billion years after its origin （© The University of Tokyo）

Within a galaxy, interstellar space is filled with thin plasma or neutral gas; however, one part of the gas forms a low temperature and high density interstellar cloud called a molecular cloud. When the gas within the molecular cloud contracts under its own gravity, it creates a new star or a cluster of new stars. A protoplanetary disk then forms around each newborn star and a new planetary system is born (Figure 4). Professor Aikawa’s group conducts research on the process of how stars and planetary systems are formed, in particular the evolution of interstellar matter. The composition of gas or solid matter (such as dust or ice) varies according to the physical environment and in many cases, the chemical reaction proceeds more slowly than the dynamical evolution of the system, which makes it possible to obtain information from the chemical composition such as the change in temperature of the gas. In fact, high-spatial-resolution observations using telescopes such as ALMA revealed the accretion of gas around young stars, disk formation and so forth, through various molecular spectra. Since these gases are taken in the disk and become materials of planetary systems, we are able to use it as a clue to explore the materials science-based origin and evolution of the planetary system.

Figure 4. An illustration of the evolution of young stars and planetary systems from a molecular cloud. (Reference: Inoue & Inutsuka, 2008; Jorgensen et al., 2012 © NAOJ)

The observation of planets that orbit around stars other than the Sun (exoplanets) is currently one of the hottest research fields in astronomy. Since the first discovery of an exoplanet 23 years ago, more than 5000 exoplanets, including planetary candidates, have been detected. To date, the primary method to search for exoplanets was an indirect method and did not capture images of primary stars and planets separately. However, it has now become possible to conduct direct imaging and spectroscopy of exoplanets due to the advancement of astronomical observational methods in recent years, such as large telescopes and adaptive optics that corrects for the atmosphere disturbance in real time and sharpens the images of stars, as well as technology such as coronagraphy, which suppresses light from overly bright primary stars. In 2009, I led an observational project called SEEDS, which used the Subaru Telescope to directly image exoplanets and protoplanetary disks. The main survey was completed in 2015 and had impressive findings, including the world’s first direct detection of a giant exoplanet around a Sun-like star (Figure 5) and the first discovery of large gaps and spiral-shaped structures of the solar-system scale within a number of planetary nurseries or protoplanetary disks. The data from these discoveries have resulted in numerous refereed papers and led to the development of next generation equipments.

Figure 5. An infrared image taken by the Subaru Telescope’s high-contrast coronagraph (HiCIAO) of planet GJ504b (point-like object located on the upper right) around the Sun-like star GJ504. The bright light of the primary star (indicated with the + symbol) spreads outward from the center. （© Astrobiology Center, National Astronomical Observatory of Japan）

In the near future we will search for life in the universe and look for not only exoplanets but also small Earth-like planets. The NASA Kepler space telescope, which was launched in 2009, has contributed to the discovery of thousands of exoplanets and numerous Earth-like exoplanets that may inhabit life (habitable planets); however, these exoplanets are too far from Earth for present-day telescopes to detect signs of life. Therefore, an innovative infrared spectroscope (IRD) was developed for the Subaru Telescope in order to explore Earth-like planets (Figure 1: Motohide Tamura, Takayuki Kotani from the Astrobiology Center, etc.). This instrument is expected to advance the discovery of habitable planets around various fixed stars (such as red dwarfs) that are near Earth. Additionally, the TESS satellite, which successfully launched in April 2018, is also anticipated to discover many transit stars around nearby fixed stars.

The examples provided above are only a few but I hope it gives you an idea about the state-of-the-art research being conducted in our Department. When looking at the development of the telescope, the so-called tools-of-the-trade in astronomy, over the span of 400 years since Galileo conducted his observations in 1609, the caliber of telescopes has surpassed the generation of 2 meter class space-based telescopes and 8 meter ground-based telescopes in terms of visible light and infrared wavelengths, and the next generation of telescopes such as 6 m space-based telescopes (JWST) and 30 m ground-based telescopes (TMT, ELT, GMT) will emerge within the next ten years. I hope that those of you who are considering studying astronomy will make full use of this perfect timing to discover uncharted knowledge in the field.

To boldly go where no man has gone before!

▶︎ Faculty Members (Left: Department of Astronomy, Hongo Campus; Right: Institute of Astronomy, Mitaka)

▶︎ For more information, please visit the Department of Astronomy homepage:
　http://www.astron.s.u-tokyo.ac.jp/en/

※ I would like to thank Professor Emeritus Takashi Onaka, Professor Tomonori Totani, Professor Nobunari Kashikawa and Professor Yuri Aikawa for their contributions to this piece.

― This article is from the 2018 "Departmental Overviews in the School of Science" series in The Rigakubu News ―

Translated by Kristina Awatsu, Office of Communication

― Office of Communication ―