今回観測された132億光年

Universe Observed through Visual Acuity of 120,000/20 [vol.2] Searching First Galaxy in the Universe

When and how were galaxies with a hundred billion stars born in the universe?
This is one of the biggest mysteries that remain unsolved in modern astronomy. The ALMA telescope took on such a difficult challenge with unprecedented high sensitivity and resolution. How close can ALMA get to the beginning of the universe? What would the first galaxy look like?
Searching for the answer, we interviewed Dr. Yoshiaki Taniguchi, a professor at the Open University of Japan. He is a specialist of galaxy research who has dedicated himself to this field of study for many years. He explained the research about the galaxy formation using ALMA.

Beauty of Spiral Galaxy Sparked Interest in Becoming Astronomer

— Can you tell me about your encounter with a spiral galaxy that led you into the path to astronomy?

Taniguchi: In my childhood, I liked to catch and collect butterflies. Maybe it came from my longing for beautiful things. When I was a junior high school student, I found a picture of a spiral galaxy in an astronomy magazine that I borrowed from a classmate. It made me wonder how the universe can create such a beautiful thing. Then I got a small telescope from my parents and joined in an astronomy club at high school and started observing stars and galaxies with fellow club members. When entering Tohoku University, I decided to study galaxies further.

 

— What kind of galaxies are there in the universe, other than spiral galaxies?

Taniguchi: Spiral galaxies have spiral structures, as suggested by its name, like the famous Andromeda Galaxy. Although our Milky Way Galaxy also looks like a spiral galaxy, it actually is categorized as a barred spiral galaxy that has a bar-shaped structure in the galactic disk. Elliptical galaxies are another type of galaxies that have round and elliptical shapes with no spiral structure. They actually have a spheroid structure that is an approximately ellipsoid shape. There are other types of galaxies such as lenticular galaxies that have an intermediate shape between a spiral galaxy and elliptical galaxy, as well as irregular galaxies that have no regular shape. All of these galaxies are categorized by their shapes.

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Upper left: Spiral galaxy Credit: NAOJ
Lower left: Barred spiral galaxy Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA); Acknowledgment: P. Knezek (WIYN)
Right: Elliptical galaxy Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration; Acknowledgment: M. West (ESO, Chile)

 

— Among them, you were particularly fascinated by the beauty of spiral galaxies.

Taniguchi: Initially I was. But as I learned more about the galaxies, I started to feel a little bit differently. Spiral and barred spiral shapes are physically beautiful. But from the viewpoint of property analysis, there is no difference between these types of galaxies. One of the major galaxy properties is the component of a galaxy; for example, what kind of stars consist of a galaxy. In this sense, I started to think the difference of galaxies in terms of shape may not be so important for the “evolution” of galaxies, no matter being a spiral or barred spiral.

 

— You mean, physical beauty of a spiral galaxy turned out to be less interesting to you as a researcher.

Taniguchi: Right. My academic curiosity moved to the galaxies that have unique properties, such as a starburst galaxy where stars are being formed at an exceptionally high rate, and an active galactic nucleus (AGN) that has a supermassive black hole at the galactic center as a source of high luminosity. Then I started working on the research of starburst galaxies. Nowadays, the word “starburst” is familiar to most people, but it was quite a new term at the time. So I was sometimes feeling small while working on my research.

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Yoshiaki Taniguchi (Professor in the Faculty of Liberal Arts at the Open University of Japan)

Dreaming to See the First Galaxy in the Universe

— You mentioned the “evolution” of a galaxy earlier. Could you explain it in more detail?

Taniguchi: In astronomy, “birth” and “evolution” are two key words in every field of research. In the field of galaxies, astronomers are aiming to find out how galaxies were formed in the history of the universe over 13.8 billion years. In other words, the goal is to solve the mystery of the birth of galaxies and furthermore the evolution process of galaxies, which has yet to be solved.

 

— The word “evolution” is familiar to us as a term of biology, but it is used in astronomy too.

Taniguchi: That’s right. For example, chemical composition of a galaxy constantly changes. At the time of the Big Bang, the universe was simply made of hydrogen and helium. Building blocks of our body such as carbon and iron are generated by fusion reaction inside stars and scattered around the space at their death, or generated by collision of neutron stars (which was in the news recently). And as a result, these materials are deposited in galactic gas. We astronomers are theoretically studying the birth and evolution of galaxies and investigating it by observations.

 

— When is it thought that the first galaxy was formed?

Taniguchi: It is thought that the first star was born in the universe when the universe was only 200 million years. Since the universe is now about 13.8 billion years, it dates back 13.6 billion years. As the first stars become the “seeds” of a galaxy, it is thought that the first galaxy was born around the same period of time. But this is only a theoretical thought because the first galaxy has not ever been observed in the universe.

 

— How can we see the birth of the first galaxy with a telescope?

Taniguchi: We need to see the farthest region of the universe. Since the speed of light has a limit (300,000 km/sec), seeing an object farther away means seeing an older picture of the object. In other words, by observing distant galaxies, we can study new-born galaxies at the early stage of the universe.

 

— A telescope is a time machine that makes it possible to go back in time and see the universe in the past.

Taniguchi: Indeed. Although no telescopes have yet to successfully observe the first galaxy in the universe, I believe ALMA can make it happen.

Yoshiaki Taniguchi (Professor in the Faculty of Liberal Arts at the Open University of Japan)

Yoshiaki Taniguchi (Professor in the Faculty of Liberal Arts at the Open University of Japan)

Born in Hokkaido in 1954. Doctor of Science. Obtained his Ph.D. in astronomy at Tohoku University. Appointed to the present post after served as a research associate at the Tokyo Astronomical Observatory of the University of Tokyo (the precursor of the National Astronomical Observatory of Japan); research associate at the Institute of Astronomy, School of Science, the University of Tokyo; associate professor of astronomy at the Graduate School of Science, Tohoku University; professor at the Graduate School of Science and Engineering at Ehime University; and director of Research Center for Space and Cosmic Evolution at Ehime University. Discovered many young galaxies surrounded by dust in the world’s first mid-infrared deep survey with ESA’s Infrared Space Observatory (ISO). Continuously playing active roles in deep surveys at far-infrared, submillimeter, and optical wavelengths as well as in exploration of distant galaxies.

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