Credit: NASA, ESA, H. Bond (STScI) and M. Barstow (University of Leicester
Researchers have discovered the most richly pulsating ultra-massive white dwarf to date — a crystallized stellar remnant that vibrates with 19 distinct modes. This discovery paves the way for future studies of the white dwarf’s interior structure and composition.
Stellar Remnants in the Instability Strip
When a star less massive than about eight times the mass of the Sun dies, it leaves behind a white dwarf: a crystallized stellar core roughly the size of Earth. With initial temperatures often higher than 105K, white dwarfs slowly cool as they age. When white dwarfs cool to a temperature around 13000K, they may enter the instability strip: a sweet spot of temperature and luminosity that causes pulsations.
Observing a white dwarf’s pulsations allows researchers to peer inside the star, precisely measuring its mass and determining its composition and interior structure. These measurements are critical for understanding the origins of ultra-massive white dwarfs — those at least 10% more massive than the Sun. Ultra-massive white dwarfs might form through the evolution of the most massive white-dwarf progenitor stars, or they might be the result of a merger of two lower-mass white dwarfs.
A Search for Massive Pulsators To date, researchers have detected pulsations from just a handful of ultra-massive white dwarfs. Of these known pulsators, only one, with eight pulsation modes detected, has provided data detailed enough to allow researchers to investigate the white dwarf’s interior. Francisco De Gerónimo (Astrophysics Institute of La Plata, Argentina) and collaborators aimed to increase those statistics with a search for pulsations in ultra-massive white dwarfs.
De Gerónimo and collaborators began their search with a list of more than 12,000 white dwarfs within 326 light-years of the Sun. To find ultra-massive white dwarfs that are likely to be pulsating, the team selected from this list white dwarfs that are at least as massive as the Sun and have temperatures that should place them in the instability strip.
Observing a white dwarf’s pulsations allows researchers to peer inside the star, precisely measuring its mass and determining its composition and interior structure. These measurements are critical for understanding the origins of ultra-massive white dwarfs — those at least 10% more massive than the Sun. Ultra-massive white dwarfs might form through the evolution of the most massive white-dwarf progenitor stars, or they might be the result of a merger of two lower-mass white dwarfs.
A Search for Massive Pulsators To date, researchers have detected pulsations from just a handful of ultra-massive white dwarfs. Of these known pulsators, only one, with eight pulsation modes detected, has provided data detailed enough to allow researchers to investigate the white dwarf’s interior. Francisco De Gerónimo (Astrophysics Institute of La Plata, Argentina) and collaborators aimed to increase those statistics with a search for pulsations in ultra-massive white dwarfs.
De Gerónimo and collaborators began their search with a list of more than 12,000 white dwarfs within 326 light-years of the Sun. To find ultra-massive white dwarfs that are likely to be pulsating, the team selected from this list white dwarfs that are at least as massive as the Sun and have temperatures that should place them in the instability strip.
De Gerónimo et al. 2025
Fuel for Future Findings
This article focuses on one white dwarf in the team’s sample, WD J0135+5722, which De Gerónimo and coauthors observed with the 10.4-meter Gran Telescopio Canarias and the 3.5-meter Astrophysical Research Consortium telescope at Apache Point Observatory. Applying Fourier transforms to the hours of observations, the team extracted the periods and amplitudes of the white dwarf’s pulsations.
In total, they detected 19 distinct pulsation modes in WD J0135+5722, with periods ranging from 137 to 1,345 seconds. This is by far the most pulsation modes detected in an ultra-massive white dwarf to date, opening the door for a detailed investigation of its composition and interior.
While that investigation is still pending future work, De Gerónimo’s team was able to estimate the white dwarf’s mass from the existing data. Since the composition of WD J0135+5722’s core is unknown, the team used several models to estimate the mass. If the white dwarf’s core is composed of oxygen and neon, as is expected for an ultra-massive white dwarf, its mass is 1.118 solar masses. If instead the core is carbon and oxygen — possible, but less likely — its mass is larger, 1.135 solar masses. Be on the lookout for more information about this pulsating white dwarf in the future!
In total, they detected 19 distinct pulsation modes in WD J0135+5722, with periods ranging from 137 to 1,345 seconds. This is by far the most pulsation modes detected in an ultra-massive white dwarf to date, opening the door for a detailed investigation of its composition and interior.
While that investigation is still pending future work, De Gerónimo’s team was able to estimate the white dwarf’s mass from the existing data. Since the composition of WD J0135+5722’s core is unknown, the team used several models to estimate the mass. If the white dwarf’s core is composed of oxygen and neon, as is expected for an ultra-massive white dwarf, its mass is 1.118 solar masses. If instead the core is carbon and oxygen — possible, but less likely — its mass is larger, 1.135 solar masses. Be on the lookout for more information about this pulsating white dwarf in the future!
By Kerry Hensley
Citation
“Discovery of the Richest Pulsating Ultramassive White Dwarf,” Francisco C. De Gerónimo et al 2025 ApJL 980 L9. doi:10.3847/2041-8213/adad73
