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| The Evolution of a "Blue Lurker" Star in a Triple System. Panel 1: A triple star system with two Sun-like stars in a close orbit, and a third star in a wider orbit. Panel 2: The close pair spirals together and merges into a single, more massive star. Panel 3: The merged star becomes a giant, expanding and transferring material to the outer companion, causing it to grow and spin faster. Panels 4-5: The central star burns out, forming a white dwarf, while the outer companion spirals inward, forming a tighter binary system. Panel 6: The surviving companion, a "blue lurker," appears like a normal Sun-like star but with subtle signs of its turbulent past: it’s slightly brighter, bluer, and spins rapidly. |
The name "blue lurker" might evoke images of a shadowy villain in a superhero tale, but in reality, it refers to a rare and fascinating class of star. NASA's Hubble Space Telescope recently delved into this cosmic mystery by studying the open star cluster M67, located about 2,800 light-years from Earth. Here, Hubble uncovered the secrets of the blue lurker, a star that has led a tumultuous life and reveals unexpected characteristics.
The blue lurker shares similarities with "blue stragglers," stars that are hotter, brighter, and bluer than expected. These stars are often the result of stellar mergers, and the blue lurker appears to have undergone a similar transformation. This particular star's behavior is unusual in that it spins much faster than typical stars of its kind. While most Sun-like stars take about 30 days to rotate once, the blue lurker completes a full rotation in just four days. This accelerated spin suggests that the star has siphoned material from a companion, triggering its rapid rotation.
Emily Leiner, from the Illinois Institute of Technology, explains that the blue lurker’s existence is the result of a complex evolutionary history. Initially, the star orbited a binary system with two other Sun-like stars. However, around 500 million years ago, these two stars merged, creating a massive star. This giant then expelled material that was absorbed by the blue lurker, causing it to spin faster. Today, the blue lurker is part of a triple-star system, orbiting a white dwarf—the remnant of the merged massive star.
The study of the blue lurker's spin and its connection to the white dwarf provides a rare glimpse into the evolution of multiple star systems. These triple-star systems, while not uncommon, can lead to fascinating and explosive outcomes. However, understanding their full evolutionary paths remains challenging for astronomers, as no model yet exists that can accurately map these complex processes.
Through ultraviolet spectroscopy, Hubble also observed the white dwarf companion orbiting the blue lurker. The data revealed that the white dwarf is unexpectedly hot, reaching temperatures as high as 23,000 degrees Fahrenheit—about three times that of the Sun’s surface. Additionally, it is heavier than anticipated, weighing in at 0.72 solar masses instead of the expected 0.5 solar masses. This supports the theory that the white dwarf resulted from the merger of two stars in the original triple system.
"This is one of the only triple systems where we can tell a story this detailed about how it evolved," Leiner noted. "Triple systems are emerging as a key player in producing interesting and potentially explosive stellar phenomena."
These groundbreaking discoveries were presented by Leiner at the 245th meeting of the American Astronomical Society in Washington, D.C.
NASA's Hubble Space Telescope continues to provide invaluable insights into the universe. After more than three decades of operation, it remains a crucial tool in expanding our understanding of stellar life cycles, cosmic interactions, and the vast mysteries of the cosmos. The telescope is a collaboration between NASA and the European Space Agency (ESA), with operations managed by NASA's Goddard Space Flight Center and support from Lockheed Martin Space and the Space Telescope Science Institute.
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