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Stellar cannibalism: Scientists find the remnants of devoured stars

A team of astronomers has made a significant breakthrough in understanding the life cycle of close binary star systems. 

Using the advanced capabilities of Georgia State’s Center for High Angular Resolution Astronomy (CHARA) Array, the experts detected the dim glow of stellar remnants that have been devoured by companion stars, a phenomenon known as stellar cannibalism.

The CHARA Array

The CHARA Array, which is located in Mount Wilson, California, employs six telescopes spread across its summit to function as a single colossal telescope with a diameter of 330 meters. This unique setup allows astronomers to observe stars with very small angular separations – a task that is impossible with conventional telescopes. 

This technique, along with the use of sophisticated MIRC-X and MYSTIC cameras developed at the University of Michigan and Exeter University, respectively, enabled the researchers to detect the faint light of stripped stars next to their brighter, predatory companions.

Rapidly rotating stars

The research was led by postdoctoral research associate Robert Klement. It was focused on a collection of “Be stars” – rapidly rotating stars that are thought to have unusual orbiting companions. 

Be stars are among the fastest rotating stars in the universe, spinning so quickly that they eject gas from their equatorial regions, forming a distinctive orbiting gas ring. 

The origin of these Be stars has long intrigued astronomers, with prevailing theories suggesting that they are the result of intense interactions and mass transfer between close binary stars.

Observing a stellar corpse

Binary star systems, especially those with small separations, experience a complex evolution. As these stars age and expand, the gas from one star can start to flow to its companion, effectively feeding the latter and causing it to spin faster. This mass transfer can strip the donor star of nearly all its gas, leaving behind a hot, dense core – what Klement and his team refer to as the “stellar corpse.”

Until now, the existence of these stripped stars was largely theoretical, as detection proved elusive due to their faintness and close proximity to their bright companions. However, the precision of the CHARA Array has enabled astronomers to directly observe the remnants of stellar cannibalism for the first time. 

Stripped stars

In his two-year observation program, Klement discovered faint light from stripped companions in nine out of 37 surveyed Be stars, focusing on seven targets to track the orbital motion around the Be stars. 

“The orbits are important because they allow us to determine the masses of stellar pairs,” explained Klement. “Our mass measurements indicate that stripped stars lost almost everything. In the case of the star HR2142, the stripped star probably went from 10 times the mass of the Sun down to about one solar mass.”

Broader implications 

The findings from this survey not only confirm the cannibalistic nature of some binary star systems, but also open new avenues for understanding more about star evolution. 

“This survey of Be stars – and the discovery of nine faint companion stars – truly demonstrates the power of CHARA,” said Alison Peck, a program director in the National Science Foundation’s Astronomical Sciences Division. “Using the array’s exceptional angular resolution and high dynamic range allows us to answer questions about star formation and evolution that have never been possible to answer before.”

Douglas Gies, director of the CHARA Array, noted that the research has finally uncovered a key hidden stage in the lives of close stellar pairs.

“The CHARA Array survey of the Be stars has revealed directly that these stars were created through a wholesale transformation by mass transfer,” said Gies. “We are now seeing, for the first time, the result of the stellar feast that led to the stripped stars.”

The study is published in The Astrophysical Journal.

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