Hidden within the star-rich fields of Cassiopeia, the HB3 supernova remnant spans an immense 1.5° × 2° region of the sky. Estimated to have formed around 40,000 years ago, this ancient stellar explosion has left behind an intricate web of diffuse shockwaves and ionized gas. Situated near the more prominent IC 1705 (the Fish Nebula) and IC 1805 (the Heart Nebula), HB3 remains a challenging target due to its extremely faint emission.

Captured from Ager, Lleida, Spain, this deep exposure also reveals two planetary nebulae—PN G132.8+02.0 and PK131+02.1 (Abell 3)—delicate reminders of the quieter stellar deaths that contrast with HB3’s violent past. The image highlights the complexity of the interstellar medium, where remnants of stellar life cycles blend into the cosmic landscape, shaping the future of star formation.

SNR G132.7+1.3, known as HB3, stretches across a massive 1.5° x 2.0° in the sky as one of the largest supernova remnants in our galaxy. Despite its size, this remnant is faint in the OIII wavelength, demanding a dedicated 140 hours of exposure to bring out its delicate structure. Captured in LRGB-HOO, this image is our most ambitious project yet, completed in collaboration with the AAA team.