U-M technology is helping astronomers open new windows into novae, stellar explosions that can act as 'laboratories for extreme physics'
Study: Multiple outflows and delayed ejections revealed by early imaging of novae (DOI: 10.1038/s41550-025-02725-1)
An international team of astronomers, including researchers from the University of Michigan, has captured unprecedented images of two stellar explosions-known as novae-within days of their eruption.
Catching these novae so early in the act provides new evidence that such explosions are more complex than previously thought.
The study, published in the journal Nature Astronomy, used a technique called interferometry at the Center for High Angular Resolution Astronomy, or CHARA, Array in California. This approach allowed scientists to combine the light from multiple telescopes, achieving the sharp resolution needed to directly image the rapidly evolving explosions.
"These aren't the first novae to be imaged, but there haven't been very many," said John Monnier, a co-author of the new study and U-M professor of astronomy. "We're showing that we're getting better at taking these images and making it easier to do so."
The study was funded by NASA, and the CHARA Array was created with support from the U.S. National Science Foundation. Instruments used on the study-namely, the MIRC-X and MYSTIC beam combiners-were also created with support from the NSF and the European Research Council in collaboration with the University of Exeter.
Novae occur in systems with two large celestial bodies: a "regular" star and a white dwarf, which is the hot, compact core of a previously much larger star. The white dwarf steals material from its companion star until it accrues enough to detonate a runaway nuclear reaction on its surface. Until recently, astronomers could only infer the early stages of these eruptions indirectly, because the expanding material appeared as a single unresolved point of light.
"Instead of seeing just a simple flash of light, we're now uncovering the true complexity of how these explosions unfold. It's like going from a grainy black-and-white photo to high-definition video," said Elias Aydi, lead author of the study and assistant professor of physics and astronomy at Texas Tech University. "These observations allow us to watch a stellar explosion in real time, something that is very complicated and has long been thought to be extremely challenging."
The best there is at what they do
The U-M contingent of the team helped develop the software and hardware to combine light from the multiple telescopes in the array. The resolution of the image produced by the array is determined by the separation between its constituent telescopes, compared with more conventional telescopes that have a resolution determined by the size of their mirrors.
For comparison, the JWST space telescope uses a 20-foot-plus mirror to produce its stunning images. Meanwhile, CHARA's telescopes are separated by 300 yards.
"In terms of resolution, we have the imaging ability of a telescope that's three football fields across," Monnier said. "It's the world's highest resolution in that regard, so we're making the best images you can make using these facilities."
The team used this technique to image two different novae that erupted in 2021. One, Nova V1674 Herculis, was among the fastest on record, brightening and fading in just days. Images revealed two distinct, perpendicular outflows of gas-evidence that the explosion was powered by multiple interacting ejections.
The second, Nova V1405 Cassiopeiae, evolved much more slowly. It held onto its outer layers for more than 50 days before finally ejecting them, providing the first clear evidence of a delayed expulsion. When the material was finally expelled, new shocks were triggered.
The team was able to develop and verify these interpretations using data from other observatories, including the International Gemini Observatory and NASA's Fermi Large Area Telescope.
"Novae are more than fireworks in our galaxy-they are laboratories for extreme physics," said Laura Chomiuk, a co-author from Michigan State University and an expert on stellar explosions. "By seeing how and when the material is ejected, we can finally connect the dots between the nuclear reactions on the star's surface, the geometry of the ejected material and the high-energy radiation we detect from space."
The findings challenge the long-held view that nova eruptions are single, impulsive events. Instead, they point to a variety of ejection pathways, including multiple outflows and delayed envelope release, reshaping our understanding of these cosmic blasts.
"This is just the beginning," Aydi said. "With more observations like these, we can finally start answering big questions about how stars live, die and affect their surroundings. Novae, once seen as simple explosions, are turning out to be much richer and more fascinating than we imagined."
