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Research Unveils Negative Superhump in Binary Stars
UNLV-led study offers new explanation for mysterious brightness variations in cataclysmic variable star systems
Mar. 24, 2026 at 4:21am
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New research from the University of Nevada, Las Vegas (UNLV) is helping to unravel the mystery behind a cosmic phenomenon known as negative superhumps in cataclysmic variable (CV) binary star systems. The study proposes that the accretion disk around the white dwarf primary star can become eccentric, or elongated, rather than circular, causing the disk to gradually rotate in a retrograde motion and produce the negative superhumps without requiring a tilted disk.
Why it matters
Cataclysmic variables have been observed for centuries, and the periodic brightness variations known as superhumps have puzzled astronomers for decades. This new model provides a more satisfactory explanation for the prevalence of negative superhumps across a wide range of CV binary star masses, clearing up issues with the previous tilted disk theory.
The details
The research team found that the eccentric accretion disk undergoes a process called retrograde apsidal precession, where the elongated disk gradually rotates its orbit over time. This natural disk eccentricity, driven by pressure, can produce negative superhumps without requiring the disk to be tilted. The model also suggests that in certain systems, disk expansion may allow for the temporary coexistence of positive and negative superhumps, and could explain how positive superhumps can occur in high mass ratio systems.
- The research paper was published on March 23, 2026 in The Astrophysical Journal Letters.
- The phenomenon of superhumps in cataclysmic variables was first identified roughly 50 years ago.
The players
David Vallet
The lead author of the study and a postdoctoral researcher in the Department of Physics and Astronomy at UNLV.
Rebecca Martin
A professor in the UNLV Department of Physics and Astronomy and a co-author of the study.
Stephen Lepp
A professor in the UNLV Department of Physics and Astronomy and a co-author of the study.
Stephen Lubow
A co-author of the study from the Space Telescope Science Institute in Baltimore.
University of Nevada, Las Vegas (UNLV)
The institution where the research was conducted and the home department of the lead author and co-authors.
What they’re saying
“Cataclysmic variables have been visible to the human eye for hundreds of years, and what began as observations of a blinking light in the sky were later revealed to be one star eating another star.”
— David Vallet, Study lead author and postdoctoral researcher
“Every piece of this puzzle increases our knowledge of mechanisms that drive the evolution of our universe.”
— David Vallet, Study lead author and postdoctoral researcher
What’s next
The research team plans to focus future work on using large numerical simulations to model an evolving accretion disk and match the predicted light curve to observations, in order to further validate the eccentric disk model and explore the potential coexistence of positive and negative superhumps.
The takeaway
This new model for the formation of negative superhumps in cataclysmic variable binary star systems provides a more satisfactory explanation than the previous tilted disk theory, advancing our understanding of the mechanisms driving the evolution of the universe.
