Astronomers solve decades-old mystery of flickering binary stars

Faint flickers in the night sky have puzzled astronomers for decades. These subtle changes in brightness come from violent star systems, where one star feeds on another. Now, new research from the University of Nevada, Las Vegas, offers a clearer explanation for one of the most confusing signals these systems produce.

The study challenges a long-standing idea about how certain brightness patterns form. By rethinking the shape of matter swirling around dead stars, scientists may have solved a mystery that has lingered for nearly 50 years.

Some stars do not shine steadily. Instead, they pulse, flicker, and flare. In certain cases, that rhythm comes from a pair of stars locked in a tight orbit.

These systems, called cataclysmic variables, involve a dense white dwarf pulling material from a nearby companion star. The stolen gas spirals inward, forming a glowing disk around the white dwarf. As this material heats up, it emits light that can be seen from Earth.

At times, these systems produce dramatic bursts known as classical novae. For a brief moment, they appear as bright new stars before fading again.

But even outside these bursts, astronomers have noticed smaller, repeating changes in brightness. These patterns, known as superhumps, do not match the simple rhythm of the stars’ orbit. Instead, they appear slightly longer or shorter than the orbital cycle.

For decades, scientists have struggled to explain why.

“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,” said David Vallet, lead author and postdoctoral researcher at UNLV.

There are two types of these brightness shifts. Positive superhumps last a bit longer than the orbital period. Negative superhumps, however, occur slightly faster than the orbit.

The second type has proven especially difficult to understand.

For years, the leading explanation suggested that the disk of material around the white dwarf tilts at an angle. Like a spinning top, this tilted disk would wobble backward over time. That motion, called retrograde precession, could explain the shorter brightness cycles.

But there was a problem. Scientists could not explain how the disk became tilted or how it stayed that way.

The physics did not fully support the idea. Forces inside the disk should quickly flatten it out. Without a clear mechanism to maintain the tilt, the theory remained incomplete.

This gap pushed researchers to search for a better explanation.

The new study proposes a different view. Instead of tilting, the disk may stretch into an elongated shape.

In this model, the disk becomes slightly oval rather than perfectly circular. Over time, this stretched shape slowly rotates backward in space. This motion is known as retrograde apsidal precession.

As the disk rotates, it changes how light is emitted. That shifting pattern creates the observed brightness variations.

The key insight is simple. The disk does not need to tilt at all.

“While observations of superhumps date back to the 1970s, we believe the eccentric disk model clears up prevailing concerns of the tilted disk model and explains the prevalence of negative superhumps across a wide range of binary star masses,” Vallet said.

This idea resolves a major weakness in earlier theories. It relies on known physical processes, rather than requiring a tilt that is difficult to sustain.

The shape of the disk plays a powerful role in how these systems behave. Even a slight stretch can change how gravity and pressure act within the disk.

As material moves through this uneven structure, it creates repeating patterns in brightness. These patterns match what astronomers observe as negative superhumps.

The model also explains why these signals appear across many different systems. Because the mechanism depends on disk shape and internal forces, it can occur under a wide range of conditions.

In some cases, the disk may even support two behaviors at once.

The researchers found that in certain systems, both positive and negative superhumps can appear at the same time. This has puzzled astronomers for years.

The new model offers a possible answer.

As the disk grows, its inner and outer regions can behave differently. One part may rotate in one direction, while another region moves in the opposite direction. This split can produce two distinct brightness patterns at once.

These overlapping signals tend to be temporary, which matches what astronomers see in observations.

The findings suggest that small changes in disk structure can lead to complex, shifting patterns of light.

The research team plans to test their model further using large computer simulations. These simulations will track how disks evolve over time and how their light patterns compare with real observations.

By matching predicted brightness curves to telescope data, scientists hope to confirm the theory.

“Every piece of this puzzle increases our knowledge of mechanisms that drive the evolution of our universe,” Vallet said.

The work represents a step toward understanding not just these systems, but the broader physics of how matter behaves in extreme environments.

At first glance, these flickering signals may seem small. But they reveal powerful processes unfolding far beyond Earth.

In these systems, gravity pulls matter into violent motion. Heat builds, light bursts outward, and structures form and shift in ways that challenge simple models.

By refining how scientists understand these disks, the study helps clarify how energy and matter move in binary star systems.

It also shows how long-standing mysteries can sometimes be solved by changing perspective. Instead of asking how a disk tilts, the researchers asked how it might stretch.

That shift in thinking opened a new path forward.

This discovery helps scientists better understand how matter behaves in extreme cosmic environments. By explaining how brightness patterns form, the research improves how astronomers interpret signals from distant star systems. This can lead to more accurate models of binary stars and how they evolve over time.

The findings may also support future studies of accretion disks in other contexts, including systems involving black holes and neutron stars. These disks play a central role in how energy is released across the universe. Understanding their structure and motion can improve predictions about cosmic events.

In the long term, clearer models can guide how telescopes are used to study variable stars. Researchers can better identify patterns, classify systems, and track changes across time. This strengthens the broader effort to map how the universe changes and evolves.

Research findings are available online in The Astrophysical Journal Letters.

The original story "Astronomers solve decades-old mystery of flickering binary stars" is published in The Brighter Side of News.

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