Hubble Reveals Distinct Origins of Rare Star from Stellar Collision

Astronomers utilizing the Hubble Space Telescope have made a significant discovery, revealing that a seemingly ordinary white dwarf star, identified as WD 0525+526, is actually the product of a dramatic stellar merger. This breakthrough, detailed in a study led by Snehalata Sahu and Boris Gaensicke from the University of Warwick in the U.K., challenges previous assumptions about the origins of white dwarfs scattered throughout the universe.

Located approximately 128 light-years from Earth, WD 0525+526 initially appeared conventional when observed through visible light. However, subsequent analysis with Hubble’s ultraviolet instruments uncovered signs of a more turbulent formation history. Gaensicke, a professor of physics at the University of Warwick and principal investigator of the Hubble program, emphasized the importance of this finding, stating, “It’s a discovery that underlines things may be different from what they appear to us at first glance.”

Insights into Stellar Evolution

White dwarfs are the dense remnants of stars similar to our sun that have exhausted their nuclear fuel and collapsed into objects roughly the size of Earth. Typically, these stars evolve predictably during their final life cycle. WD 0525+526, however, deviated from this norm, emerging from the violent merger of two stars rather than the conventional pathway of a single star’s demise.

The study indicates that this merger event resulted in significant alterations to the star’s atmospheric composition, revealing subtle but detectable traces of its explosive origins. Analysis of WD 0525+526 uncovered an unusual abundance of carbon in its atmosphere, a hallmark of stars formed through such collisions. In typical white dwarfs, hydrogen and helium layers obscure carbon-rich cores, making this discovery particularly notable.

Gaensicke and his team found that during the merger, the intense forces stripped away the outer layers of the star, allowing carbon to rise to the surface. While such signals are elusive in visible light, they become pronounced in ultraviolet wavelengths, where Hubble excels.

Significance of the Discovery

WD 0525+526 stands out even among the limited number of known merger remnants. With a surface temperature nearing 21,000 Kelvin (approximately 37,000 degrees Fahrenheit) and a mass 1.2 times that of the sun, it is both hotter and more massive than other stars in this rare category. The study’s findings suggest that many more white dwarfs may harbor similar explosive origins.

Antoine Bedrad, a researcher at the University of Warwick who co-led the study, expressed a desire to extend this research further. “We would like to explore how common carbon white dwarfs are among similar stars and how many stellar mergers are hiding among the normal white dwarf family,” he stated. This research could significantly advance our understanding of white dwarf binaries and their pathways to supernova explosions.

The findings were published on August 6, 2023, in the journal Nature Astronomy. As astronomers continue to analyze these cosmic phenomena, the implications of such discoveries may reshape our understanding of stellar evolution and the lifecycle of stars in our universe.