Mosaic image of M31 generated using SWarp. The locations of all the novae detected in the archival images are marked in the figure. Credit: Basu, J. et al 2024 ApJ 971/ CC BY 4.0
New insights into ‘novae’, stars that run out of fuel and explode violently, show that some are 10,000 times brighter than the Sun1.
Located at the centre of the Andromeda galaxy, the stars plunge into a dormant stage before and after such intense activity and emit ultraviolet light.
Analysis of novae is important because they churn out life-brewing elements heavier than hydrogen and spill them into star-forming regions in space, says a team of astronomers at the Indian Institute of Astrophysics in Bengaluru.
Previous studies have explored novae at visible wavelengths but not when they emit ultraviolet light. This survey analysed archival ultraviolet radiation data of novae captured by the Ultraviolet Imaging Telescope onboard the AstroSat, an Indian space-based observatory in low-earth orbit.
The researchers considered 42 novae detected within 20 days before eruption in the outburst phase and at the quiescence or dormant stage. Almost 90% are around the centre of the Andromeda galaxy. This region is shrouded by galactic light that can hide such stars.
Two specific methods were used to remove light contamination, exposing 23 dormant novae, 21 at post-outburst and 4 during both the dormant and outburst phases.
Most novae are white dwarfs that accrete matter from companion stars. The researchers say the majority of ultraviolet radiation originates from the stars’ accretion disk in quiescence.
