Scientists discover that massive be stars could be “triples”

University of Leeds scientists have unveiled a groundbreaking revelation that challenges conventional wisdom about massive Be stars. In a paper titled “Gaia uncovers difference in B and Be star binarity at small scales: evidence for mass transfer causing the Be phenomenon,” Ph.D. student Jonathan Dodd and Professor René Oudmaijer present compelling evidence suggesting that these stars, previously believed to be mainly in double star systems, might actually be “triples.”

This discovery has the potential to reshape astronomers’ understanding of Be stars, a subset of B stars crucial for developing theories on stellar evolution. Characterized by a gas disk akin to Saturn’s rings, Be stars have puzzled scientists for 150 years since Italian astronomer Angelo Secchi first identified them in 1866. The prevailing view linked the disk formation to rapid star rotation induced by interactions in binary systems. However, this newfound evidence introduces a transformative perspective on the formation of these enigmatic celestial bodies.

Triple systems

In a notable twist, Mr. Dodd, the corresponding author of the study, drew an intriguing parallel, likening the discovery to the dual suns seen in Star Wars planets. Leveraging data from the European Space Agency’s Gaia satellite, the researchers assert that these massive Be stars may actually exist in triple systems, challenging the previously held belief in binary arrangements.

New research using data from ESO’s Very Large Telescope and Very Large Telescope Interferometer has revealed that HR 6819, previously believed to be a triple system with a black hole, is in fact a system of two stars with no black hole. The scientists, a KU Leuven-ESO team, believe they have observed this binary system in a brief moment after one of the stars sucked the atmosphere off its companion, a phenomenon often referred to as “stellar vampirism”. This artist’s animation shows what the system might look like; it’s composed of an oblate star with a disc around it (a Be “vampire” star; foreground) and B-type star that has been stripped of its atmosphere (background). Credit: ESO/L. Calçada.

Mr. Dodd elucidated, “Our observation method involved tracking star movements over extended periods, about 10 years and shorter spans like six months. A straight trajectory indicates a lone star, while a subtle wobble or, optimally, a spiral suggests multiple bodies. Surprisingly, when comparing B stars and Be stars, it initially seems that Be stars have fewer companions, defying expectations.”

However, Principal Investigator Prof Oudmaijer interjected, suggesting, “The absence of apparent companions might stem from their current faintness, eluding our detection capabilities.”

Mass transfer

Turning to an alternative dataset, the researchers delved into the realm of more distant companion stars. Strikingly, they unearthed a convergence in the rates of companion stars at these extended separations, bridging the gap between B and Be stars.

This revelation led to the inference that a third star often enters the cosmic stage, coercing the companion closer to the Be star. This proximity facilitates mass transfer, giving rise to the distinctive Be star disk. The vanishing act of these companions, obscured by the voracious appetite of the “vampire” Be star, renders them too diminutive and faint for detection.

Artist’s impression of a vampire star (left) stealing material from its victim: New research using data from ESO’s Very Large Telescope has revealed that the hottest and brightest stars, which are known as O stars, are often found in close pairs. Many of such binaries will at some point transfer mass from one star to another, a kind of stellar vampirism depicted in this artist’s impression. Credit: Pic credit: ESO/M. Kornmesser/S.E. de Mink

This groundbreaking insight not only challenges our comprehension of massive stars but also ripples across various astronomical domains. Prof Oudmaijer noted, “A revolution is unfolding in physics with gravitational waves, and our findings offer a key to deciphering these enigmatic sources. As we explore the cosmos, the intricate dance of triple stars emerges as a pivotal aspect, reshaping our understanding beyond the realm of binaries. Triples, it seems, have become the new binaries.”

Source: University of Leeds

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