Our story takes place in the northern part of Chile in South America, where the Atacama Highlands stretch 160 kilometers from east to west and 1,000 kilometers from north to south, sandwiched between the Andes Mountains and the Pacific coast. With its barren deserts that resemble the landscape of Mars, it’s known as the driest part of the world. Here, on the summit of the 5,640-meter high Cerro Chajnantor, construction of the University of Tokyo Atacama Observatory (TAO) is underway. Professor Takashi Miyata is one of the long-time leaders of this project and is responsible for the fabrication of the primary mirror and observation instruments.
“We’re aiming for completion in 2023, but we’ve already been certified by Guinness World Records as the world’s highest observatory,” says Professor Miyata with a smile.
The TAO telescope’s primary mirror (the main concave mirror that collects light in a reflecting telescope) is huge, with an aperture of 6.5 meters and a weight of 8.3 tonnes. The incident beam from the telescope can be switched into three different foci, at which separate, large instruments are mounted. It is one of the best observatories in the world in both scale and observation technology.
But why build this observatory on at the top of a high mountain, anyway? And on the other side of the world, in Chile?
“The atmosphere gets in the way of ground-based observations. Light from celestial objects hundreds of millions of light years away comes all the way to Earth, but is absorbed by our atmosphere and disappears a few tenths of a second before it reaches us on the ground. That’s a waste. So we wanted the observatory to be as high as practicable and to collect the maximum amount of light with a large aperture telescope. To do this, we needed to build the observatory in as high a location as possible where the air is thin.”
In the electromagnetic spectrum, infrared rays in particular are readily absorbed by water vapor. For this reason, it is important not only for the telescope site to be at a high altitude, but also to be dry and without rain. The Atacama Highlands satisfy all these conditions.
“Our first task was to go to the summit of Cerro Chajnantor to see if it was really a suitable place for our observatory. When I joined the project in 2000, no-one had climbed the mountain before. On the first-ever ascent in 2002, in which I participated, we drove up the mountain to 5,000 meters and walked from there. Standing at the summit, I was convinced that this location was as good as I thought it would be. Having said that, the climb was very tough. There’s very little oxygen in the air at that altitude, only half that available at sea level. I was in such excruciating pain that I wanted to go home right then and there (laughs)! But the thin air means that the infrared rays from space aren’t lost, so in that sense, the more uncomfortable it is, the more suitable the location.”
If that’s the case, why not just make observations from satellites like the James Webb Space Telescope (JWST)? There are some things that only ground-based telescopes can do, counters Professor Miyata.
“For example, when it comes to searching for distant faint objects, ground-based observatories are no match for the JWST. On the other hand, ground-based observatories are clearly superior when it comes to observing the same star for a long time, or quickly pointing the telescope at a suddenly developing event in the universe. It’s also easier to use a ground-based observatory for high-risk and challenging projects.”
Space telescopes and ground-based observatories share roles and complement each other’s work. However, there is something that only a ground-based observatory can offer, and that is, provide observing opportunities to students. Professor Miyata stresses the importance of this role, pointing to why universities build observatories. That’s the reason he’s willing to go to all this effort.
“The construction of the TAO began with the building of a road to the top of the mountain. In the beginning, the road was barely wide enough for one car, and of course there were no guardrails, so we had to navigate many switchbacks to reach the summit. It was pretty hair-raising (laughs). I’ve been to Cerro Chajnantor as many as 10 times a year. The flights alone took three days for the round trip, so I hate to think that I spent a month out of the year on a plane (laughs).”
Mid-infrared imaging captures gas and dust in space
MIMIZUKU—an abbreviation for Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe—is one of the observation instruments that Professor Miyata has developed and built. Officially, it is a mid-infrared imager and spectrograph located at the Cassegrain focus of the TAO telescope, but put simply, it is a huge, two-meter-high, ultra-sensitive infrared camera. MIMIZUKU covers the mid-infrared wavelength range of 2 to 38 micrometers (µm), and has the world’s highest resolution of 1 arcsecond (1,296,000th of 360 degrees) at 30 µm.
Infrared radiation is familiar to us from heaters and remote controls for home appliances. Infrared wavelengths range from 0.7 to 1000 μm: the band close to visible light is near-infrared, the band close to radio waves is far-infrared, and the band between the two is known as mid-infrared. So why does MIMIZUKU focus on this mid-infrared band? This is because it can capture matter — gases and dust — in the universe at temperatures as low as 100 to 1000 K (about -173°C to 726°C), which are difficult to observe with visible light.
“We already know much about the lifespan of a star, from its birth to just before it dies. However, a dying star expels gas into its surrounds, and that gas circulates to become a new star again, or forms a planet around a star, a process that we are yet to completely figure out. For example, we have no idea from where in the universe the gas that created our solar system and the dust that formed the Earth came. Investigating these questions with visible light instruments from the ground is difficult because the temperatures are low and the particles of matter are fluffy and minuscule. This is where infrared comes into play. In the mid-infrared band, we can see the gas and dust spreading outwards, and the fine particles of matter gathering around a star as it is born. If we can fill in the pieces of the unsolved mystery from here, we will be able to understand how matter moves around the universe.”
MIMIZUKU features a newly developed system called a simultaneous two-field observation mechanism. This enables simultaneous high-precision monitoring and precision spectroscopy for two different observation targets, allowing accurate observations to be made along the time axis: the long-awaited realization of “time-domain astronomy.”
“The starry sky looks the same every night. But sometimes, the stars suddenly glow or change in brightness. In fact, there is a great deal of information that can be gleaned from phenomena associated with these changes. For example, if you compare a normal still photo with a video, you can see from the latter that a tree is swaying in the wind, and many other things. In one sense, astronomy has always been done with still images, something that is gradually changing, and there is now a worldwide effort to observe developing astronomical phenomena on video. This is called time-domain astronomy. However, time-domain astronomical video observations in the infrared wavelengths, especially in the mid-infrared band, have rarely been attempted due to technical problems. Once we can do this, we will be able to observe, for example, the changes in the formation of a disk around a star, and we may be able to understand how planets form and how stars die, which we can’t learn from still photographs alone. This is what we’re aiming to do with TAO.”
There’s a different kind of fun in making things in astronomy
Professor Miyata is now at the forefront of trying to solve the mysteries of the universe, but surprisingly, he chose astronomy not because of his interest in distant stars, but because of his fascination with making things here on Earth.
“I had to take a practical course in my third year of studies in the Faculty of Science at Kyoto University, so I chose astronomy at the urging of a friend. As it happened, the course was in an infrared astronomy research laboratory. What we made there was a simple infrared sensor that received light collected by a small telescope, and it was a lot of fun. I was astonished by the fact that something I had created could receive light from a distant star, and that was my initiation into astronomy.”
He wants to not only look at the stars with observation equipment, but also wants to build the equipment himself. This desire from his student days still pervades Professor Miyata’s work today. In this sense, the TAO project, which involves building the world’s most advanced telescope and observation equipment, may be a crucial project for Professor Miyata.
“We astronomers really don’t want to miss a single speck of light that comes from the stars. So when I think about the TAO lenses, I know that silicon is a good material but half of the light is reflected, and I can’t bear to let it escape. Various technologies such as anti-reflection coatings have been developed for silicon lenses for visible light applications, but no anti-reflection technology had been created for the mid-infrared 30 μm band. Our solution was to fabricate fine cone-shaped structures on the surface of the lens that are smaller than the mid-infrared wavelength. Thanks to this technique, we were able to prevent reflections, allowing more light to pass through the lens. The last and most important part of the telescope contains just one of those lenses. All the other parts were made by combining mirrors. This made the design a lot more complicated.”
Professor Miyata says that he had to overcome a series of challenges like this one at a time, leading him to the following thoughts about his colleagues and students.
“I wanted to complete the telescope sooner, but it took much longer than expected. The longer the research goes on, the more graduate students who strived so hard together will graduate without being able to witness the most moving moment of receiving starlight for the first time. That’s really upsetting to me. I deeply value the fact that TAO was created with the help of so many, including our past students.”
Professor Miyata looks back fondly on the days when the road leading to the top of Cerro Chajnantor was still narrow, and he and his students took turns cooking meals in the town at the base of the mountain, living together as if it were a camping trip. He also has this message for students.
“There’s a different kind of fun in making things in astronomy than in other fields. You never know how to make something until you try it. So don’t ever think that you’re not good at making things, or limit your possibilities. Just give it a try. New experiences are exciting. I look forward to us working together.”
The world’s highest astronomical observatory is waiting for you, not wanting to miss even a single speck of light coming from the stars.”
※Year of interview:2022
Interview/Text: Minoru Ota
Photography: Junichi Kaizuka