Evolution of a Blue Lurker Star – NASA
The name “blue lurker” might conjure images of a sinister comic book villain, but in reality, it refers to an extraordinary and rare type of star. NASA’s Hubble Space Telescope recently uncovered one of these enigmatic stars in the ancient open star cluster M67, located 2,800 light-years away.
Hubble’s forensic investigation reveals a star with a chaotic past—entwined in a dramatic dance with two other stars in a gravitationally bound triple-star system. This star shares a lineage with the mysterious “blue stragglers,” which defy expectations by burning hotter, shining brighter, and appearing bluer than their counterparts. Scientists believe these stellar anomalies are born from the spectacular mergers of stars, creating a cosmic tale of destruction and rebirth written across the heavens.
“We know these multiple star systems are fairly common and are going to lead to really interesting outcomes,” Leiner explained. “We just don’t yet have a model that can reliably connect through all of those stages of evolution. Triple-star systems are about 10 percent of the Sun-like star population. But being able to put together this evolutionary history is challenging.”
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Hubble observed the white dwarf companion star that the lurker orbits. Using ultraviolet spectroscopy, Hubble found the white dwarf is very hot (as high as 23,000 degrees Fahrenheit, or roughly three times the Sun’s surface temperature) and a heavyweight at 0.72 solar masses. According to theory, hot white dwarfs in M67 should be only about 0.5 solar masses. This is evidence that the white dwarf is the byproduct of the merger of two stars that once were part of a triple-star system.
“This is one of the only triple systems where we can tell a story this detailed about how it evolved,” said Leiner. “Triples are emerging as potentially very important to creating interesting, explosive end products. It’s really unusual to be able to put constraints on such a system as we are exploring.”
The “blue lurker” stands out not for its appearance but for its extraordinary behavior—spinning far faster than expected. At first glance, it resembles an ordinary Sun-like star. The term “blue” is misleading, as its color blends seamlessly with the other solar-mass stars in its cluster. This makes it a hidden anomaly, “lurking” unnoticed among the stellar crowd.
Its rapid spin, however, reveals a dramatic past. Evidence suggests the star siphoned material from a companion, accelerating its rotation to a remarkable speed. While typical Sun-like stars take around 30 days to complete a rotation, this enigmatic star whirls through one in just four days. Its unusual spin rate was uncovered using data from NASA’s now-retired Kepler space telescope, adding yet another chapter to the fascinating story of this stellar outlier.
