The Hubble Space Telescope has identified an uncommon “blue lurker” star that has been consuming material from its two linked sibling stars.
This rapidly rotating star offers an intricate glimpse into the complex family interactions of multiple-star systems.
“It’s an excellent mid-evolution snapshot of this system, and hopefully, it will assist us in assembling a more distinct understanding of the overall development of triple systems,” Eric Sandquist, an astronomer at San Diego State University who was not part of the study, explained to Live Science.
Despite the blue lurker resembling a classic sun-like star, it rotates at a much higher speed due to the combined energy exerted by three stars. Therefore, it is “lurking” among a collection of much slower stars. The term “blue” relates to how hotter stars such as this one typically appear bluer.
The lurker belongs to the open cluster M67, also referred to as the “King Cobra Cluster.” This group of 500 stars, approximately 4 billion years old and situated 2,800 light-years away, is loosely held together by gravity. Given that all these stars share the same age, they tend to rotate at roughly the same speed — with the exception of a few surprisingly quick stars.
“A standard star in the cluster completes a rotation approximately every 25 days,” Emily Leiner, an astronomer at the Illinois Institute of Technology, stated at a Jan. 13 press conference during the 245th American Astronomical Society meeting in National Harbor, Maryland. “That’s comparable to our own sun… [The blue lurkers] were spinning around every few days.”
Consequently, Leiner and her team directed Hubble’s focus on one of these lurkers to examine what might clarify its abnormalities. They discovered that it was partnered with a white dwarf, which is the remnants of a deceased star. However, this stellar remnant was so substantial that it couldn’t have possibly originated from merely one star.
These observations narrate a tale of a challenging triplet relationship: The lurker initiated its journey by revolving around two binary stars entwined in a do-si-do pattern. Ultimately, the binary stars coalesced to form a massive star, which expanded later in its life. The lurker then extracted material from the swollen star, leading to an increase in its spin speed as the white dwarf faced its end.
“It’s not unusual for stars to undergo this mass-transfer process; what’s more challenging is discovering them,” Leiner told Live Science. Nearly 10% of stars are part of triple-star systems similar to this one, she mentioned, but it’s relatively rare for astronomers to delineate their evolutionary paths so distinctly. While the life cycle of an individual star can be predicted easily through models, multiple-star systems involve greater complexities and thus necessitate in-depth observations to begin uncovering their past.
Sandquist is keen on investigating the prevalence of blue lurkers and whether they are associated with other astronomical events, such as Type Ia supernovas — a prominent type of explosion utilized to assess the universe’s expansion rate. If lurkers of this nature are commonly responsible for Type Ia supernovae, they could not only aid in comprehending triple-star systems but also provide insights into the evolution of the universe.