Twin White Dwarf Eruptions Reveal Staged, Multi-Phase Novae — Challenging Long-Held Models

Two recent eruptions from white dwarf stars have forced astronomers to rethink a simple, single-blast model for classical novae. High-resolution observations captured striking, staged behavior in two systems—V1674 Herculis and V1405 Cassiopeiae—revealing multiple ejections and a delayed expulsion of outer layers that contradict the long-standing view of novae as instantaneous explosions.

“The fact that we can now watch stars explode and immediately see the structure of the material being blasted into space is remarkable,”

said University of Michigan astronomer John Monnier, co-author of the study published on December 5 in Nature Astronomy.

“It opens a new window into some of the most dramatic events in the universe.”

What astronomers observed

In 2021 the Center for High Angular Resolution Astronomy (CHARA) Array in California produced interferometric images of two novae in unprecedented detail. V1674 Herculis brightened and faded within days—one of the fastest novae on record—yet its ejecta showed two perpendicular gas outflows (jets), implying the nova was powered by multiple, overlapping ejections rather than a single instantaneous burst.

By contrast, V1405 Cassiopeiae evolved much more slowly: it retained its outermost layers for more than 50 days before those layers were expelled. This provided the first direct evidence for a delayed, staged ejection in a nova event. Both systems were also detected in gamma rays by NASA’s Fermi Gamma-ray Space Telescope, confirming a connection between the geometric complexity of the ejecta and high-energy emission.

“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,”

said Texas Tech astrophysicist Elias Aydi, a co-author on the study.

“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.”

How this was possible

The breakthrough came from interferometry, which combines light from multiple telescopes to achieve far higher resolution than a single instrument can provide. Interferometric imaging made it possible to resolve rapidly changing geometry in the ejected gas and directly observe jets and layered expulsions. The same technique has been used to image the Milky Way’s central black hole and other compact, dynamic sources.

Implications for nova theory and astrophysics

These results challenge decades-old assumptions that novae are single, brief explosions. Instead, novae can be multi-stage, with both rapid and delayed mass-loss episodes. That complexity affects how we interpret gamma-ray production, the link between surface nuclear burning and mass ejection, and the binary interactions that drive these outbursts. Researchers say the new observations will help refine theoretical models of white-dwarf accretion, thermonuclear ignition, and shock-driven high-energy emission.

“Novae are more than fireworks in our galaxy—they are laboratories for extreme physics,”

said Michigan State University astronomer Laura Chomiuk.

“By seeing how and when material is ejected, we can connect the dots between nuclear reactions on the star’s surface, the geometry of the ejected material, and the high-energy radiation we detect from space.”

Who was involved

The findings, published December 5 in Nature Astronomy, result from a collaboration of multiple institutions including the University of Michigan, Texas Tech University, Michigan State University, and the CHARA Array team. The combined interferometric and gamma-ray data give a richer, multiwavelength picture of how novae unfold in real time.