New Caltech Model Reveals Asymmetric Mass Ejection in Dying Sun-like Stars

Jim Fuller’s Caltech Model Reveals Asymmetric Mass Ejection in Dying Stars

The transformation of a star like our Sun into a white dwarf has long been viewed as a relatively orderly process. As these stars exhaust their fuel, they swell into red giants and gradually drift off their outer layers, leaving behind a dense, cooling core. Because this is the fate of most stars, white dwarfs are among the most common stellar remnants in the universe. However, a new model presented at the 248th meeting of the American Astronomical Society in Pasadena suggests that this transition is, in fact, a chaotic, violent affair.

The 248th American Astronomical Society Meeting Highlights Chaotic Red Giant Ejections

The Mechanism of ‘Stellar Kicks’

Jim Fuller, a professor of theoretical astrophysics at the California Institute of Technology, proposes that the mass loss during the red giant phase is not a smooth, symmetrical flow. Instead, the star ejects blobs of material in random, asymmetric bursts. Each ejection acts as a propulsion event, pushing the star in the opposite direction. The study has been submitted to the Publications of the Astronomical Society of the Pacific.

In this model, blobs of matter are chaotically being ejected from the surface of the bloated stars in an asymmetric fashion, Fuller said in a press release. And every time that happens, the star gets a little kick in the opposite direction. Like Newton said, for every action there is an equal and opposite reaction.

According to Fuller’s calculations, a star in the final stages of its life could experience roughly 10,000 of these small kicks over several hundred thousand years. Each individual push would move the star at only a few meters per second. That’s a slow jogging pace for humans, Fuller said. However, because the kicks occur repeatedly, they add up over time through a mathematical process known as a random walk. Much like a person wandering in random directions eventually ends up far from where they started, the star gradually begins to move in one direction. Researchers estimate the final velocity of the resulting white dwarf could reach roughly 1 kilometer per second.

Kareem El-Badry’s Observations of Widely Separated Binary Star Systems

Impact on Binary Star Systems

This model offers a possible explanation for a long-standing mystery surrounding white dwarfs: why widely separated binary star systems appear to be less common once one of the stars evolves into a white dwarf. Previous research by Kareem El-Badry, an assistant professor of astronomy at Caltech, found that widely separated pairs of stars are less common after one member of the pair becomes a white dwarf. His observation suggested white dwarfs receive a kick strong enough to disrupt their orbits.

Fuller’s model suggests the white dwarf receives a net velocity boost that can have major consequences for some binary star systems. If the orbital speed of the binaries is less than the kick speed, the wide binaries will become gravitationally unbound, Fuller said. This displacement is sufficient to disrupt the delicate gravitational balance holding wide binary pairs together, causing them to drift apart.

Publications of the Astronomical Society of the Pacific Reviewing Potential Stellar Collisions

Future Observations and Stellar Collisions

Beyond explaining the separation of binary stars, the model indicates that the process is much gentler than the blast of a supernova, which can launch a stellar remnant in one direction at high speed. However, the accumulation of smaller kicks still carries weight. In some cases, the repeated kicks could even lead to stellar collisions, resulting in explosive events that astronomers might observe. While this model provides a physical explanation for observed phenomena, future studies could further test these theories. Searching for evidence of stellar collisions and other predicted signatures could validate or refine this model, offering a clearer view into the chaotic final moments of Sun-like stars.

Sources: Sciencedaily, Tasnimnews.