NOIRLab Nuggets

Gemini Observes Ultra-Hot Nova Eruption

4 April 2025

Astronomers have made a new discovery in the world of novae: a phenomenon that can be thought of as erupting “zombie stars.” High-mass stars end their lives in an explosive event called a supernova, while low-mass stars typically fade into white dwarfs. However, a white dwarf in a binary system, gravitationally bound to another star still fusing elements in its core, can also experience a dramatic end-of-life event called a nova. 

White dwarfs bound to living stars can accrete mass from their partners. This process creates an atmosphere on the white dwarf and can eventually generate enough heat to reignite the fusion process in the once-dead star, creating a sort of “zombie star.” However, the star’s return to life does not last forever. This reignition expels the new atmosphere in an extremely bright event known as a nova.

Almost all known novae have erupted only once. However, a small group of novae, less than a dozen, have been discovered to erupt periodically — a strange phenomenon known as recurrent novae. These novae are not well understood, and astronomers continue to gather data to create a clearer picture of what is physically happening in these stellar systems. 

Recently, astronomers have gathered more information about these peculiar events by studying a system named LMC 1968-12a (LMC68) located in the Large Magellanic Cloud. Astronomers have observed a recurrent nova explosion in this system every 4 years since its discovery in 1990.

In August 2024, astronomers completed the first near-infrared spectroscopic observation of a recurrent nova outside the Milky Way on LMC68. Follow-up observations were conducted nine days after the initial outburst with the Carnegie Institution’s Magellan Baade Telescope, and 22 days after the initial outburst with the Gemini South telescope, one half of the International Gemini Observatory, funded in part by the U.S. National Science Foundation and operated by NSF NOIRLab.

Spectroscopy is a technique in which light is captured and spread into a spectrum. This allows scientists to identify the chemical elements present in the light through a unique pattern of gaps in the spectrum called absorption lines. Here, researchers specifically looked at the near-infrared region of the electromagnetic spectrum to glimpse into the nova’s ultra-hot phase, during which many elements were highly energized. 

From this study, researchers found that ionized silicon, in particular, dominated the material from the eruption, emitting light almost 100 times brighter than the Sun. The temperature detected from the eruption was extreme, one of the hottest ever recorded, at 3 million degrees Celsius (5.4 million degrees Fahrenheit). The current understanding is that white dwarfs accreting lighter elements in their environment, like the ones that exist in the Large Magellanic Cloud, need to collect large amounts of matter before becoming hot enough to explode. This creates a far greater outburst than other novae previously observed.

Studies will continue to investigate how chemical elements in a white dwarf’s environment affect its behavior in novae and the overall process that leads to recurrent novae. 

You can read the NOIRLab press release here.

To learn more about white dwarfs, including what happens when they become structurally unstable and explode entirely, visit Vera C. Rubin Observatory’s Exploding Stars investigation. The activity introduces students to supernova light curves and how Type Ia supernovae, which also occur in white dwarf binary systems, can be used to measure cosmic distances in the universe. 

Contacts

Nicole Kuchta
Communications Intern 
NSF NOIRLab
Email: nicole.kuchta@noirlab.edu

Phoebe Dubisch
Communications Intern
NSF NOIRLab
Email: phoebe.dubisch@noirlab.edu