On May 19, the amateur Japanese astronomer Koichi Itagaki discovered a supernova in the Spiral Galaxy M101, 21 million light-years away. The event, named SN2023ixf, is the closest to Earth in five years and the second found in M101 in the past fifteen years. Mr. Itagaki alerted his professional colleagues, who immediately trained telescopes on the event. Dr. Andy Howell of Las Cumbres Observatory, who is the head of the Global Supernova Project, has directed LCO’s network of telescopes to image SN2023ixf as its light continues to fade. The story of how Koichi Itagaki discovered the supernova and the response of the astronomical community was beautifully described by this article in the journal Science.
The Global Supernova Project was designed by Dr. Howell for exactly this situation. With early and continuous data from the event, members of the Global Supernova Project have already made interesting discoveries about SN2023ixf. Dr. Howell started Tweeting about the supernova soon after discovery, causing many amateur astronomers to analyze their data and notice they had images of the supernova exploding even before it was discovered.
Three recent publications detail unusual features of the supernova:
Dr. Griffin Hosseinzadeh of the University of Arizona, who was a graduate student with Dr. Howell, published a paper in the Astrophysical Journal Letters examining the early light curve of the supernova, bringing together amateur and professional data. His group found that the Type II supernova is consistent with the explosion of a red giant star. They also found that the supernova behaved like none ever seen during the earliest observations. “We either caught the star in the act of losing its outer layers, or we saw the explosion running through material that the star lost earlier,” says Dr. Hosseinzadeh. “We’re still not sure!”
Dr. Azalee Bostroem, also of the University of Arizona, has submitted a paper to the Astrophysical Journal Letters with early results for SN2023ixf. While the previous paper examined the light emitted by the supernova, this paper considers the evolution of the spectrum of that light. “We called in every favor that we had to obtain over four spectra per night for the first five nights,” remembers Dr. Bostroem. This group has found that the composition of the light changed rapidly by the day as the supernova continued. This led to the finding that the mass around the star that exploded was distributed asymmetrically, and not smoothly. “Never before have we obtained such a detailed picture of the supernova and the material surrounding it,” notes Dr. Bostroem. “It is really testing our understanding of how stars lose mass and how we interpret observations of other supernovae.”
Dr. Daichi Hiramatsu of Harvard University, who was also a graduate student of Dr. Howell, has had a paper published in the Astrophysical Journal Letters that has the supernova’s discoverer, Koichi Itagaki, as a coauthor. This paper is the official discovery paper of the supernovae. "On Friday evening at a brewery, I got an email from Koichi Itagaki about this discovery. I immediately opened up my laptop and triggered the LCO network and the Swift UV space telescope to capture its early evolution,” Dr. Hiramatsu describes the excitement of the moment. “These observations have revealed peculiar increasing temperature evolution indicating the SN light emerging from the dense circumstellar material from very recent mass loss.” The authors also looked at the data that existed prior to the supernova explosion and were able to quantify that the star lost as much as the mass of our sun in the year or two leading up to the explosion.
Together, these and other papers are causing scientists to rethink what happens in the final days of a star’s life. The exploding star is so far away that astronomers can’t make out its details in photographs. And it has long been a mystery what happens just before a star explodes, because there is rarely preexisting data on a star to examine, and astronomers almost never catch a supernova within hours of explosion as they did this time.
The founder of the Global Supernova project, Dr. Howell says, “In the last few years there’s been a revolution in understanding what happens to stars as they die. They don’t just go quietly – they convulse in violent fits and starts, nearly shaking apart the star, before it ultimately goes out in one giant explosion. We still don’t know why they do that, but this is our best look yet at the process.”
The scientists add that these types of supernovae are important because they help us probe the limits of physics. In the explosion, while most of the outer layers of the star are flung off into space, the core of the star collapses, and leaves behind either a neutron star or a black hole. A neutron star is a star composed almost entirely of neutrons – more than the mass of our Sun, but packed into the size of a city. It is the most extreme form of matter we can study since we can’t see inside a black hole.
“In this stellar death there is new life – a new star is born“ adds Dr. Howell. “We don’t know exactly why some supernovae lose their outer layers millions of years before they explode, and some keep them right up until the years before they die. But in studying those death throes we can learn more about the extreme stellar birth that occurs too – the creation of a neutron star or black hole.”
Overall, a dozen of the authors of these papers are scientists who trained at Las Cumbres Observatory.
The vision of the Global Supernova Project - building a world-wide community of scientists specializing in supernovae - is proven to be a tremendous success with events such as SN2023ixf. The sharing and rapid communication among members of the scientific community can generate research results in real-time that lead to greater discoveries in astronomy.
“We built Las Cumbres Observatory, and the Global Supernova Project, precisely to study supernovae at a moment’s notice, and to be able to study them around the clock,” adds Dr. Howell. “It is incredibly rewarding to see it all pay off with observations we could not have obtained at a more traditional facility of a single telescope at a single location. I’m also very happy that we could work together with fellow amateur astronomers to piece together the puzzle. People, around the world, no matter their cultural background, appreciate the night sky. Yet we can all come together to find out new things about the lives and deaths of stars.