💥 Two nova explosions "photographed" with exceptional resolution

Nova explosions, which were thought until now to be relatively simple, are actually turning out to be very different. An international team has published in Nature Astronomy images with unprecedented detail, revealing multiple ejections of matter and unexpected delays.

These phenomena occur when a white dwarf, the remnant of a star, accumulates gas from a stellar companion. The resulting thermonuclear explosion was, however, difficult to examine directly, as conventional telescopes only perceived it as a bright point. Consequently, astronomers had to deduce the mechanisms from indirect signals, which limited their understanding of the initial phases of these eruptions.


To overcome this difficulty, the CHARA Array in California used interferometry. This technique combines light from six telescopes, simulating a giant instrument with exceptional resolution. In this way, researchers were able to image the novae shortly after their triggering, following the evolution of these structures in real time.

The first nova studied, V1674 Herculis, exploded in 2021 and faded within a few days, a record for speed. The images reveal two perpendicular gas flows, indicating multiple explosions. Significantly, these structures coincide with the detection of gamma rays by NASA's Fermi telescope, directly linking matter collisions to high-energy emissions.

For its part, the second nova, V1405 Cassiopeiae, also dates from 2021. It exhibits different behavior with a slow evolution. Surprisingly, it retained its outer layers for more than 50 days before ejecting them. This observation provides the clearest evidence to date of delays in matter expulsion. During the final ejection, new shock waves formed, once again producing gamma rays detected by Fermi.


These discoveries help explain the powerful shock waves in novae, which are sources of gamma-ray radiation. The Fermi telescope played a key role in establishing this link, making novae laboratories for studying shock physics. Laura Chomiuk of Michigan State University notes that seeing how matter is ejected makes it possible to articulate nuclear reactions, flow geometry, and high-energy radiation.

The ability to resolve such details comes from interferometry, complemented by spectra from observatories like Gemini. John Monnier of the University of Michigan calls this advance extraordinary, opening a new window on these types of cosmic events. Elias Aydi, the lead author, compares it to going from a grainy photo to a high-definition video.