Buzz
In this artist's depiction, a deceased star is accompanied by a fragmenting asteroid. Stocktrek ImagesIn approximately 5 billion years, when our sun exhausts its hydrogen fuel, it will expand into a massive red giant, violently ejecting hot plasma layers and scorching the inner planets. The aftermath will be an expanding shell of cooling gas, forming a stunning planetary nebula with a luminous white dwarf at its core, gleaming like a stellar diamond. While this destiny is certain for our sun, the fate of its planets, particularly Earth, remains uncertain.
Researchers from the University of Warwick, U.K., have attempted to address this question, developing a basic "survival guide" for planets in such dire circumstances. Although Earth's future remains unclear, the study, featured in the Monthly Notices of the Royal Astronomical Society, suggests that smaller planets are more likely to endure the harsh conditions near a white dwarf.
What’s the reason behind this? Observations reveal that numerous white dwarf star systems are surrounded by dust, and spectroscopic analysis confirms that this dust contaminates the stars' atmospheres. The conclusion is evident: These systems once hosted rocky planets, along with asteroids and comets, which were ripped apart and pulverized into dust due to intense tidal forces exerted by the white dwarf.
Radius of Destruction
Why do planetary bodies disintegrate in white dwarf orbits? These dense stellar remnants pack nearly the entire mass of their progenitor stars into a compact Earth-sized sphere of degenerate matter. This extreme density generates an immensely strong gravitational field and tidal forces. If a planet ventures too close, the tidal force on the side facing the white dwarf becomes far stronger than on the opposite side. Beyond a critical distance—marked by a foreboding dusty ring called the "destruction radius"—the tidal forces overwhelm the planet's structure, tearing it apart.
To determine the destruction radius for planets of varying sizes, the researchers simulated the dynamics of different planets orbiting a sun-like star as it evolves into a red giant and eventually becomes a white dwarf. This chaotic phase disrupts planetary orbits, either dragging them into the white dwarf’s destructive grasp or ejecting them into wider orbits.
Viscosity Is Everything
The researchers discovered that a planet’s vulnerability to tidal forces isn’t solely determined by its mass and composition but also by its viscosity—the resistance to deformation. Low-viscosity exoplanets, similar in consistency to Saturn’s moon Enceladus, would be destroyed if they orbit within five times the white dwarf’s destruction radius.
On the other hand, high-viscosity planets could survive if they orbit at least twice the destruction radius. Astronomers recently identified a dense heavy metal object near a white dwarf, embedded in a dusty disk. This object, likely the metallic core of a larger planet, survived the tidal destruction of its outer layers.
As exoplanet detection methods advance, more planets in white dwarf systems will be discovered. The researchers aim for these simulations to serve as a framework for understanding the composition and behavior of such exoplanets.
But What of Earth?
While the simulations offer valuable insights into planetary survival near white dwarfs, they focus on homogeneous objects. Earth’s complex structure presents a more intricate scenario, making its fate harder to predict.
"While our study is advanced in many ways, it focuses solely on homogeneous rocky planets with uniform internal structures," explained lead author Dimitri Veras in the University of Warwick's accompanying press release. "Calculating the behavior of a multi-layered planet, such as Earth, is far more complex, but we are exploring the possibility of tackling this challenge as well."
In short, to survive in a close orbit around a white dwarf, it’s best to be small, dense, and composed of heavy metals. As for Earth’s ultimate fate, it remains uncertain—though it’s safe to say you wouldn’t want to be around when our sun transforms into a red giant and turns up the heat.
Discover more about the cosmos in Sara Gillingham’s illustrated book "Seeing Stars: A Complete Guide to the 88 Constellations." At Mytour, we recommend titles we believe you’ll enjoy, based on the stories you read. If you decide to purchase, we may earn a share of the sale.
Long before the sun exhausts its hydrogen and expands into a red giant, it will grow significantly hotter, bombarding the inner planets with intense radiation. Combined with powerful solar winds, this will likely strip away Earth’s atmosphere, eradicating any remaining life in the process.
