For Koichi Itagaki, it was just another evening of supernova hunting. After his usual 7 p.m. dinner with his wife, he drove to his private observatory in the hills above his home in Yamagata, Japan, 290 kilometers north of Tokyo. He set out treats for the only visitors he allows on his celestial patrols: a stray cat he calls Nora and the raccoon dogs that warily approach from the surrounding forest. He then took a seat within his “headquarters,” a cozy hut equipped with a bed, minifridge, microwave—and a dozen monitors used to control seven telescopes at three locations across Japan.
On clear nights, each telescope runs through a routine, focusing on one of the approximately 1000 galaxies Itagaki monitors for two 15-second exposures before swiveling to the next target. On this night, clouds blanketed most of the country, leaving a clear view only for his two telescopes in Okayama, 700 kilometers to the southwest. But as the clock ticked into the early morning of 20 May, clouds drifted over Okayama, too. Itagaki called it a night and drove home, leaving the telescopes on automatic in case the weather cleared.
It did. The next morning he had scanned the night’s images for just 5 minutes when he spotted a new, bright object in a spiral arm of the Pinwheel galaxy, 21 million light-years away. “It was so bright, I thought there was no way this object could have been missed,” he says. To his surprise, he was the first to post the news to the Transient Name Server (TNS), the International Astronomical Union’s database of new celestial objects. As word spread on TNS and the Astronomer’s Telegram, an email alert service, professionals and amateurs alike began pointing their instruments toward SN 2023ixf, the universe’s newest exploding star and the closest to Earth in a decade. It was growing brighter by the minute.
For Itagaki, an amateur astronomer and semiretired snack food executive, such discoveries are routine. SN 2023ixf is his 172nd supernova, a total topped only by U.S.-based Tim Puckett, whose private observatory in Georgia has bagged at least 360 supernovae with the help of a worldwide network of volunteers who manually examine his images. Itagaki, by contrast, works alone. He “is one of the most prolific supernova observers in the world,” says Andrew Howell, an astronomer at the University of California (UC), Santa Barbara.
But his achievement goes beyond numbers, Howell says. “The really special thing is that so many of the supernovae he finds turn out to be interesting.” Although his formal education ended with high school, Itagaki has also co-authored a couple dozen scientific papers. “He’s self-trained, so that’s really incredible,” says Daichi Hiramatsu, an astronomer at the Center for Astrophysics | Harvard & Smithsonian.
Amateurs have a long tradition of contributing to astronomy. Before the advent of large survey telescopes, they discovered many of the asteroids and comets that swing close to Earth. They have discovered galaxies and nebulae too dim and diffuse for large telescopes to notice. And they are now discovering planets outside the Solar System. But even among this storied population of hobbyists, Itagaki stands out “not only for his success, but also for his dedication,” says Jeremy Shears, former president of the British Astronomical Association, which supports amateurs.
CHEERFUL, FRIENDLY, and easy-going, Itagaki is a trim 75-year-old with wisps of white hair, wire-rimmed bifocals, and a self-effacing sense of humor. “I am not an astronomer,” Itagaki says, smiling broadly while waving his left hand dismissively, as if shooing away a fly. “I’m looking for new celestial bodies as a hobby.” He traces his path into astronomy to a boyhood fascination with lenses. “I used to play with lenses, using sunlight to burn paper,” he says. In junior high, he spent his allowance on a DIY telescope kit and studied the Moon a bit. “I also used it to spy on the neighbors,” he says, smiling and waving.
Then in 1963, a 19-year-old Japanese amateur named Kaoru Ikeya grabbed national headlines when he discovered a comet with a more substantial homemade telescope. “It amazed me that you could search the stars like this,” Itagaki says. Within Itagaki’s hut, a framed 1963 newspaper clipping of Ikeya’s achievement hangs in homage.
After high school, Itagaki went to work at a local confectionary company, saving up to buy a 15-centimeter telescope with which he discovered his first comet at age 20. He joined Itagaki Peanuts, a snack food company started by his father, and eventually became its CEO. He is credited with being the first in Japan to sell snack “minipacks” that provide just a mouthful of peanuts, cashews, or candy-coated almonds. As the business prospered, Itagaki says he “invested a lot” in his passion—perhaps as much as the cost of typical Japanese house, he estimates. At age 60, he turned over operations of the 30-employee firm to his sons so he could devote himself to astronomy.
Like Ikeya and many other amateurs, Itagaki started out watching for comets. But in 1998, NASA set up a near-Earth object program, which enlisted major observatories to detect and track threatening celestial bodies. It left little room for amateur discoveries. So in 2000, “I gave up on comets and started searching for supernovae,” Itagaki says.
To escape Yamagata’s lights, Itagaki rented a plot in the hills above the city, and over time added the stainless-steel domes that now house his 60-, 50-, and 11-centimeter telescopes. About 8 years ago he set up the second observatory in Okayama, and 5 years ago he added a third observatory with another two telescopes in Kochi, 800 kilometers away on Shikoku, the smallest of Japan’s four main islands.
The geographic distribution means at least one of the observatories is in the clear almost every night. “I don’t think there’s anyone else in the world who has a network of telescopes operated in such a way,” says Hiramatsu, who adds that Itagaki also has an advantage in spotting supernovae that first appear during Japan’s nighttime because Asia lacks a big survey. And whereas the big observatories tend to watch distant galaxies, Itagaki concentrates on nearby ones, where any supernovae can be studied when they are intrinsically fainter, says Azalee Bostroem, an astronomer at the University of Arizona. “This means they are discovered younger and can be observed later, sometimes years after the explosion,” she says.
SN 2023IXF SHOWS how Itagaki gets the jump on other observers. Monika Soraisam, an astronomer at the Gemini Observatory, had written a program to automatically alert her to supernova candidates caught by the Zwicky Transient Facility, a survey using the 48-inch telescope at the Palomar Observatory in California. “I had the alert in my inbox the same night that Itagaki made his observations but did not have the time to follow up until later,” she says.
Alex Filippenko, an astronomer at UC Berkeley, also missed the discovery. During a backyard star-viewing party the night of 18 May, he says he imaged the Pinwheel galaxy with an 11-centimeter telescope “just for fun.” After hearing of SN 2023ixf’s discovery, Filippenko found that he had serendipitously captured the supernova 11 hours before Itagaki. “Had I closely examined my images, I would have discovered it even earlier than Itagaki!” he says.
There is more at stake than bragging rights. “The sooner after the explosion that a supernova is detected, the more we can potentially learn about the exploding star and the explosion itself,” Filippenko says. Four days after its discovery, SN 2023ixf peaked in brightness at about magnitude 11—still too faint to be seen with the naked eye but as bright as Proxima Centauri, the Sun’s nearest neighbor. By then, numerous telescopes had tuned into the spectacle—including giants such as the 8.1-meter Gemini North telescope in Hawaii. NASA’s Hubble and JWST space telescopes are also observing the supernova, which will fade over the course of many months.
Analysis of the light curve suggests the exploding star was a red supergiant hundreds of times bigger than the Sun. Having exhausted its nuclear fuel, the star’s core collapsed, launching a shock wave that blew apart the star and produced a cosmic light show. In 2002 images from the Hubble telescope, Soraisam and her colleagues found what they believe is the progenitor. But she says they won’t know for sure until “after the supernova has faded and we see that the star has vanished.”
Howell says the critical data from Itagaki and other amateurs indicate an early, extra brightening of SN 2023ixf that supernova models don’t predict. He points to three possible explanations for the excess light: a precursor explosion or eruption; dense shells of material around the star, lit up by the emerging shock wave; or unusual emissions from a nonspherical progenitor star. It is unlike anything seen before, “probably because we almost never catch supernovae this early,” Howell says.
Itagaki’s previous discoveries suggested it might be possible to see signs of unrest on a massive star even before it explodes. In 2004, he spotted a bright object in a spiral galaxy 77 million light-years away from Earth. No professionals verified his sighting before it disappeared 10 days later. Following a hunch it could be important, Itagaki periodically checked the location. In 2006, he (and two other amateur astronomers all working independently) discovered supernova 2006jc.
The explosion produced unexpected x-rays that Andrea Pastorello, an astronomer at Italy’s Astronomical Observatory of Padova, thought were a clue to the 2004 outburst. Pastorello and his team concluded that what Itagaki saw was the progenitor star shedding its outer layers in a burst of light. Those layers lit up again with x-rays 2 years later when the supernova ejecta caught up and collided with the shed material.
It was previously thought that stars were quiet before going supernova. Itagaki’s glimpse of that 2004 precursor event along with other observations is “really causing a big shift in our understanding of supernovae,” Howell says.
FOR DISCOVERING and explaining the never-before-seen phenomenon, Pastorello’s team and Itagaki were rewarded with a paper in Nature in 2007. It was Itagaki’s first scientific publication, and supernova 2006jc remains his most memorable discovery. “But I had absolutely nothing to do with the paper; it just has my name on it,” he says with that smile and self-deprecating wave.
Since then, Pastorello has worked with Itagaki on five other papers. “He is very collaborative, and his archive is a precious source of pre-explosion data,” Pastorello says. That collaborative spirit has earned Itagaki co-authorship on what he estimates are “a lot” of papers, though he doesn’t know how many. The Astrophysics Data System, operated by the Smithsonian Astrophysical Observatory, credits Itagaki as a co-author on 23 refereed publications and identifies scores more that cite his data. Papers from SN 2023ixf are likely to add to the tally.
SN 2023ixf has started its long fade out, but Itagaki’s passion isn’t dimming. Although already “superaged” by Japan’s definition, he sees no reason to alter his routine. He’s determined to catch a supernova going off in the Andromeda galaxy, the Milky Way’s nearest neighbor, one that by cosmic averages is long overdue. He returned to his headquarters the night after finding SN 2023ixf for another solitary vigil.
“When I was in junior high school, I dreamed of building a hut, putting a big telescope in it, and having this life,” he says. “That dream has come true.”
