“Not Our Everyday Supernova”: Superluminous Supernova Brings Together Collaborators Across the World
A global team of researchers has coalesced around the discovery of one of the most distant, extremely bright supernovae ever found, highlighting the collaborative nature of modern astronomy. The unique benefits of Maunakea as a site for cosmos exploration and the unparalleled power of W.M. Keck Observatory’s instruments made this discovery possible. The results have been published in the Astrophysical Journal Letters.
A supernova is an extremely powerful, bright explosion of a dying star. When a massive star dies, it creates a supernova that can be as bright as an entire galaxy, lasting weeks to months, before it collapses and forms a black hole or a neutron star, or completely dissolves into a diffuse nebula. A superluminous supernova is an exceptionally bright star explosion event, a rare subclass of supernovae.
For lead researcher Joel Johansson of Stockholm University in Sweden, supernovae are a crucial tool to understanding the universe. “We can use supernovae like rulers to measure the distance and speed of expansion of the universe,” he said. This discovery fits into a wider debate in astronomy right now — trying to nail down the expansion rate of the universe, known as the Hubble constant — and provides a new method of quantifying it.
Space’s Magnifying Glass
This new superluminous supernova called SN 2025wny was magnified, or gravitationally lensed, by two galaxies. Gravitational lensing, one of the fundamental predictions of Einstein’s theory of relativity, happens when a distant object is closely aligned with a nearer galaxy — or in this case, two — in our line of sight. The light emitted from the distant supernova SN 2025wny was magnified and distorted by the gravity of the foreground galaxies, allowing us to see something much farther away than would normally be visible with current technology. Observatories on Maunakea have had great success in imaging distant objects recently thanks to gravitational lensing, like the James Clerk Maxwell Telescope’s discovery of 13 distant, dusty galaxies.
So how can gravitational lensing help us find how fast the universe is expanding? When you have a foreground galaxy as a lens, the light emitted from the supernova takes the shortest paths around the galaxy — but each path takes a different amount of time. “So in this case, we ended up with four images of the same supernova that reached us at slightly different times,” explained Joel. (These four are the bright dots A, B, C, and D in the figures, while Gal 1/Gal 2 are the foreground galaxies.) Those time delays give us a direct measure of how much the universe grew during the time it took the light to reach Earth.
In the case of SN 2025wny, the images arrived with a 10-30 day delay between them — ideal timing for the research team. “What made us really excited was that here, finally, we found something that was bright enough for us to observe with small- to modest-sized ground telescopes, and the images were separated further in time. You don’t have to go to space or use adaptive optics to see it,” said Joel, because the time delay is large enough.
The Search for the Supernova
The journey to finding SN 2025wny began in a tiny 1-meter telescope in California, and ultimately many different ground-based telescopes around the world came together to image and categorize the supernova. “Early on, Shri Kulkarni [former head of the Caltech Optical Observatory (COO), which oversees Keck and Palomar] made a point that in astronomy, you need to have a logical chain of discovery.” Joel elaborated. SN 2025wny was first detected by the Zwicky Transient Facility at Palomar Observatory in California during a routine monitoring of the night sky. While small, Zwicky finds around 100 new supernovae each night.
SN 2025wny was of interest, so the next step in the chain was to observe in more detail, which requires a bigger telescope. If that turns out to be interesting, you get an even bigger telescope, Joel explained. This brought SN 2025wny to two different telescopes on La Palma in the Canary Islands — the Nordic Optical Telescope and Liverpool Telescope — who provided early measurements and images of the supernova. From the early data from La Palma, Joel’s team could say it was probably a supernova, but it was really odd — “it was not our everyday supernova we see.”
This intrigue brought them to the next step in the chain of discovery: “If it’s really, really interesting, then you go after it with Keck!” said Joel. Finally, Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS) nailed down the final measurements of the supernova, where researchers discovered that SN 2025wny was indeed unlike your regular supernova. Not only is SN 2025wny the first gravitationally-lensed Type I superluminous supernova, it’s one of the most distant supernovae ever seen — 10 billion light-years away. This provides us a look back in time to some of the earliest days of the universe, when it was only four billion years old. Researchers hope to find supernovae of all ages in order to splice together how the Hubble constant has changed over time.
Now, SN 2025wny has captured the attention of both Keck researchers and other astronomers worldwide. Keck has continued observing SN 2025wny every night since the team discovered it in September, and will do so for many months. Joel explained that this paper is just the tip of the iceberg — SN 2025wny’s time in the spotlight is just beginning. “Even just ten minutes observing with Keck is mind-blowing,” said Joel, and now with months of continuous data collection, the work soon to come is sure to be thrilling. “In some sense it’s kind of bizarre that despite being one of the most distant supernovae found, thanks to the magnification boost it will be one of the most well-studied supernova ever,” Joel laughed.
Many Hands make Supernovae Visible
This was all made possible through the wide web of global connections that astronomy brings together. “For us in Stockholm, it’s such a blessing to have these friends on Maunakea and Caltech,” Joel said. While the Swedish team of researchers could call on telescopes elsewhere in the world, like the European Southern Observatory’s Very Large Telescope (VLT) in Chile, many of them are difficult to access, with formal applications and long wait times.
This discovery is thanks to Keck Observatory’s Target of Opportunity (ToO) policy, which allows scientists to request immediate access to the telescope for a short-lived cosmic opportunity, like a comet or a supernova. Without the ToO policy, many more brief events like this supernova would pass us by before scientists got the opportunity to image or measure them.
The connection between many telescopes allowed lots of astronomers to work on this discovery. The great thing about collaborating with such a large team is that there is a huge diversity of interests, said Joel, which means that “there’s goodies for everyone” in the spectra produced at Keck. One dataset provides endless opportunities to explore, whether you’re interested in cosmology like Joel, or the exact physics of star explosions, or even if you aren’t crazy about supernovae but instead curious about the lens and host galaxies. “A big team of people who are nerdy about different things is awesome,” he said. “Everyone gets to chip in.”
For Joel, one of the main reasons he was motivated to pursue astronomy was a visit to the Nordic Optical Telescope at La Palma as a graduate student. “You can feel the whole building vibrate as the telescope starts moving,” he described. “And then when you go outside — you will never see the night sky like that from anywhere else.” Maunakea Observatories know how transformative in-person opportunities are for our relationships to astronomy. Maunakea Scholars connects local high school students with observing time at the telescopes, and Akamai Scholars is a paid summer internship where local college students work directly with a mentor on a project at one of the observatories. And for kamaʻāina of all ages, the Kamaʻāina Observatory Experience is a free all-inclusive tour of the telescopes on Maunakea on the first Saturday of each month. These opportunities can transform how we view and engage with astronomy — academically, culturally, and on a deep personal level. “Opportunities for future astronomy students to get up there in person are so important,” Joel described, that we should strive to provide for future generations.
2026: Year of the Supernova?
This collaboration will only grow bigger with the Legacy Survey of Space and Time (LSST) commencing this year, centered at the Vera C. Rubin Observatory in Chile. This telescope will do the same type of sky survey as the Zwicky one that first detected SN 2025wny, but much, much larger. With an 8-meter mirror, LSST will be able to see much deeper in time to the earliest days after the Big Bang. Now that they have a method for systematically finding these lensed supernovae, Joel and his team predict a large leap in supernovae discovered from the LSST in Chile. “In 2026,” Joel said, “we think this stuff is going to totally explode” — both figuratively, and literally.
