Impression of a comet-like object falling towards a white dwarf
Australian scientists have found further evidence of stars swallowing planets or planetary material. Image by EPA PHOTO
  • science and technology

Planet-eating twins revealed by Australian astronomers

John Kidman March 24, 2024

At least one in a dozen stars show evidence of planetary ingestion, according to Australian scientists. 

That might not sound earth-shattering in itself but literally could be, with a capital “e”.

Much of the research into the concept of planet-eating has focused on the formation of Jupiter and the discovery that beneath the swirling vortex clouds in its upper atmosphere lie the remnants of countless baby planets.

Had these so called planetesimals not been gobbled up by the gas giant, as astronomers believe, some may eventually have become proper planets just like Earth.

But the scenario doesn’t stop there, with some experts suggesting Earth may yet suffer a similar fate billions of years down the track as the Sun runs out of fuel, expands and similarly devours everything within its reach.

Until now, it’s just been a theory.

However, an international team led by Australia’s ASTRO 3D project has placed planetary ingestion a step closer to reality by studying apparent differences in the make-up of twin stars, which should, by definition, exhibit the same composition.

“They are born of the same molecular clouds and so should be identical,” Monash University research fellow and lead author Fan Liu explained.

“(But) thanks to very high precision analysis, we can see chemical differences … this provides very strong evidence one of the stars has swallowed planets or planetary material and changed its composition.”

ASTRO 3D research associate, Professor Fan Liu
 Fan Liu says there’s strong evidence of stars consuming planets or planetary material. Image by HANDOUT/MONASH UNIVERSITY 

The phenomenon appeared in about eight per cent of the 91 pairs of twin stars examined.

What makes the study compelling is that the stars were in their prime of life – so-called main sequence stars, rather than final phase red giants, as the Sun is eventually expected to become.

There is room for doubt as to whether the stars are swallowing planets whole or engulfing protoplanetary material but Dr Liu suspects both are possible.

“It’s complicated,” he said.

“The ingestion of the whole planet is our favoured scenario but of course we can also not rule out that these stars have ingested a lot of material from a protoplanetary disk.”

The findings have wide-ranging implications for the study of the long-term evolution of planetary systems.

“Astronomers used to believe these kinds of events were not possible but from the observations in our study, we can see that, while the occurrence is not high, it is actually possible,” according to ANU professor and co-author Yuan-Sen Ting.

“This opens a new window for planet evolution theorists to study.”

ASTRO 3D director Professor Emma Ryan-Webber says the findings contribute to the big-picture quest to determine the chemical evolution of the universe.

“Specifically, they shed light on the distribution of chemical elements and their subsequent journey, which includes being consumed by stars,” she said.

The team’s dataset was collected using the 6.5-metre Magellan Telescope, the European Southern Observatory’s Very Large Telescope in Chile and Hawaii’s Keck Telescope.