An international group of astronomers, including researchers from the University of Michigan, has obtained detailed images of two novae within days of their eruption. These early observations provide new insights into the complexity of such stellar explosions.
The research, published in Nature Astronomy, used interferometry at the Center for High Angular Resolution Astronomy (CHARA) Array in California. By combining light from several telescopes, scientists achieved high-resolution images that captured the rapid changes during these events.
“These aren’t the first novae to be imaged, but there haven’t been very many,” said John Monnier, a co-author and professor of astronomy at the University of Michigan. “We’re showing that we’re getting better at taking these images and making it easier to do so.”
Funding for the study came from NASA and the U.S. National Science Foundation (NSF). The CHARA Array’s development was supported by NSF, while instruments like MIRC-X and MYSTIC were created with help from both NSF and the European Research Council in partnership with the University of Exeter.
Novae occur when a white dwarf star collects material from a companion star until a nuclear reaction erupts on its surface. In previous studies, astronomers could only infer early stages indirectly because expanding material appeared as an 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 and assistant professor 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.”
Researchers at the University of Michigan contributed by developing software and hardware for combining telescope data within CHARA’s array. The resolution depends on telescope separation; CHARA’s telescopes are spaced 300 yards apart—equivalent to having an imaging capability similar to a telescope three football fields wide.
“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 imaged two novae from 2021: Nova V1674 Herculis brightened and faded quickly and showed two perpendicular gas outflows—evidence for multiple interacting ejections. Nova V1405 Cassiopeiae evolved more slowly; it retained its outer layers for over 50 days before ejecting them in what researchers identified as delayed expulsion.
Other observatories contributed data used to verify interpretations, including those from 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, co-author from Michigan State University. “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 results challenge previous views that nova eruptions are single events; instead they suggest varied pathways including multiple outflows or delayed release.
“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.”
