Six Red Dwarfs Caught Swallowing Rocky Planets, Scientists Say
A study published in the Monthly Notices of the Royal Astronomical Society has identified six red dwarf stars with anomalously high levels of lithium in their atmospheres. Researchers propose that the most likely explanation is that these stars have recently consumed rocky planets.
Key Findings
The research team, from the University of Exeter and Keele University, analyzed data from the Gaia-ESO Spectroscopic Survey. Among thousands of stars studied, six red dwarfs in three young open star clusters—NGC 2451a, Blanco 1, and NGC 2516—were found to contain lithium levels far exceeding expected values.
- Star Clusters: The six stars are located in clusters with ages between 50 and 200 million years.
- Lithium Anomaly: These stars are otherwise indistinguishable from their cluster siblings in terms of position, parallax, and kinematics.
- Mass Estimate: Using evolutionary models, researchers estimate the lithium signal is consistent with the ingestion of between three and ten Earth masses of rocky planetary material.
Background
Red dwarf stars (M dwarfs) are common in the galaxy. Their hot interiors should rapidly destroy lithium shortly after formation. The presence of lithium indicates an external source, which researchers attribute to planet-swallowing events predicted during the early stages of planetary system formation.
"The process of finding evidence of planetary consumption is termed necroplanetology."
Alternative Explanations Considered
The study also considered other possible causes for the elevated lithium levels:
- Magnetic Activity or Fast Rotation: These factors could inhibit lithium depletion. However, the six stars are slow rotators, making this explanation unlikely.
- Long-Lived Accretion Disk: A disk could deliver lithium later, but planetary engulfment is deemed the most plausible explanation.
Significance
The findings suggest that 2–3% of early M dwarfs and late K dwarfs may have engulfed a planet. Researchers note this could be a lower limit, as lithium may be quickly destroyed after an engulfment event.