JAXA Japan Aerospace Exploration Agency

Q. Do you think X-rays are effective for research on supernova remnants?

An image of the supernova remnant SNR 0540-69.3 in the Large Magellanic Cloud, observed by the Chandra X-ray Observatory. The white objects twinkling in the middle are high-energy particles. A cloud of high-temperature gas about 40 light years in diameter spreads around the remnant. (courtesy: NASA/CXC/SAO)

Yes. I’d say that observations to investigate the nature of supernova remnants can only be performed with X-rays. That’s because these supernova remnants have ultra-high temperatures of 10 to 100 million degrees Celsius. The rays emitted from such high temperatures are X-rays, so they can be observed only with X-ray satellites. A feature of X-ray devices is that they can see particles at ultra-high temperatures. In supernova remnants, the generation of cosmic rays can also be clearly viewed because of X-rays.

Q. What do you look forward to the most for the new ASTRO-H satellite?

ASTRO-H will be equipped with observation devices with the most advanced technologies ever. So, if these are operated as planned, it is certain that ASTRO-H will achieve results that will go down in history.
Anything could happen in space, as its environment is completely different from that of the Earth, but the world is expecting us to operate all of the devices without any problems. Personally, I strongly hope that we will succeed in this goal.
X-ray astronomy started with the X-ray astronomy satellite HAKUCHO, launched in 1979.
It achieved many excellent results, so X-ray astronomy became a Japanese specialty. Since ASTRO-H is the culmination of Japanese satellite research, I think it will present a very big opportunity for Japan to show our true abilities to the international community.

Q. Can you tell us about your major research achievements so far?

Images of the supernova remnant RX J1713.7-394. The image on the right shows a close-up image of (b) and (c) from the image on the left. The four-digit numbers are the year of observation. The X-rays that the yellow arrow points to change over time. This indicates that cosmic rays accelerate into high energy. (courtesy: Uchiyama et al. Nature 2007)

With the Japanese X-ray astronomy satellite Suzaku and the American Chandra X-ray Observatory, we observed shockwaves from a supernova remnant and captured the moment when the nonthermal particles were accelerated for the very first time.
This observation was made on supernova remnant RX J1713.7-3946, located toward the constellation of Scorpio, about 3,000 light years away. As this celestial object releases X-rays and ultra-high-energy gamma rays, which indicate the existence of cosmic rays, it was thought to be a good object to watch for potential variable X-ray emissions.
After annually researching the distribution of these ultra-high-energy particles from the supernova remnant, we noted that some X-rays have changed in images captured in the years 2000, 2005 and 2006. These changes indicate the process of nonthermal particles getting accelerated into a high-energy regime. In other words, we captured a scene of the acceleration of cosmic rays.
The main component of cosmic rays is protons, but in past supernova remnant observations, we only found electrons. However, we knew that nonthermal particles from a supernova remnant consist of protons, just like cosmic rays. Due to this, the theory suggesting that the origin of cosmic rays lies in supernova explosions has become more compelling.

Q. What is the most impressive result from Japanese X-ray astronomy satellites to date?

Through observations with the X-ray Astronomy Satellite ASCA, a group of researchers discovered the existence of nonthermal particles from a supernova remnant in the year 1995. It was concluded that these particles have very high energy. This was a world-renowned achievement. I was fascinated by it when I was a postgraduate student, and this led me to my current research.

Q. You do research overseas, Dr. Uchiyama. Can you tell us what international researchers think about ASTRO-H?

Anticipation is high among international researchers, with good reason. The Chandra X-ray Observatory and the European satellite XMM-Newton were launched in 1999. Japan’s Suzaku was launched in 2005. It has been more than ten years since the launch of the U.S. and European satellites, so we need a follow-up mission.
ASTRO-H will be the biggest X-ray astronomy mission in the world in the next decade. Scientists from the United States and Europe are part of the ASTRO-H research group, and X-ray astronomers from all over the world hold high hopes for ASTRO-H.

Q. What is the charm of astronomy for you?

It’s the endlessness of the mysteries. There are extraordinary mysteries in front of my eyes, so I feel like I’d like to solve them. There are a lot of things unknown about supernova explosions and cosmic rays, and many of these mysterious phenomena do not seem like they will be solved very easily! Because I am young I have a lot of years ahead to enjoy trying to solve this treasure box of mysteries.