Scientists have discovered a rare object called the Blue Ring Nebula, a hydrogen gas ring with a star in the center. The properties of this system suggest that this is the remnant of two stars that met their final death: an internal orbital dance that led to the merging of the two stars. The result offers a new window to the fate of many densely orbital binary star systems.
In 2004, scientists from NASAGalaxy Evolution Explorer spotted an object unlike anyone they’ve seen in ours Milky Way Galaxy: Large, faint patches of gas that appear to have a star in its center. In the ultraviolet wavelengths used by the satellite, the spot looked blue — though it didn’t actually emit light visible to the human eye — and careful observation identified two thick rings in it, so the team nicknamed it the Blue Ring Nebula. For the next 16 years, they studied it with numerous telescopes on Earth and in space, but the more they learned about it, the more mysterious it seemed.
A team of scientists, including Princeton UniversityGuðmundur Stefánsson, PhD student in astrophysical science Henry Norris Russell, combines ground-based observations with detailed theoretical modeling to study the properties of the object. The report describing their findings appeared in the November 19, 2020 issue. Nature.
“We were in the middle of an observation one night with a new spectrograph we had built recently when we received a message from our colleagues about a special object made up of nebulous gas that is rapidly expanding away from a central star,” Stephenson said. “How is it formed?” What are the properties of the central star? We were immediately excited to help solve the mystery! “
Most stars in the Milky Way are in binary systems – pairs of stars orbiting each other. If they are close enough to each other, such systems can meet their doom in a stellar merging event: As stars develop, they expand, and if they are close enough, one of the stars can swallow its orbital satellite, causing the satellite to rotate inward. until the two stars collide. As the satellite loses its orbital energy, it can eject the material away at high speeds.
Could this explain the mysterious Blue Ring Nebula?
Additional evidence to support this hypothesis comes from observations with two different spectrographs on large telescopes on Earth: the HIRES optical spectrograph of the 10-meter Keck telescope at the top of Maunakea, Hawaii, and the nearby infrared instrument for finding the planet, the 10-meter Hobby-Eberly telescope. at the McDonald Observatory in Texas, a new near-infrared spectrography that Stephenson helped design, build, and commission to detect planets around nearby stars.
The Blue Ring Nebula consists of two expanding cones of debris. The base of a cone moves towards the Earth. Both bases are outlined in purple, revealing shock waves created as the debris moves into space. Blue is the material behind the shock wave and is only visible where the cones overlap. Credit: NASA /JPL-Caltech / R. Pain
“Spectroscopic observations were key to allow us to understand the object further, from which we can see that the central star is inflated and we see signals of accumulation, probably from the surrounding disk of debris,” said Stephenson.
“In fact, spectroscopic data combined with theoretical modeling show that the Blue Ring Nebula matches the picture of a merging binary star system, suggesting that the inward-facing satellite is likely a low-mass star,” said Kerry Hodley, a postdoctoral fellow at Caltech and lead author of the article.
Although relics of several similar double fusion events have been observed before, all such objects have been shrouded in opaque dust and clouds that interfere with the appearance of the properties of the central stellar remnant. The Blue Ring Nebula is the only object that allows an unobstructed view of the central stellar remnant, offering a clear window in its properties and giving clues to the merging process.
“The Blue Ring Nebula is rare,” Hodley said. “As such, it is really exciting that we were able to find it and we are excited to be able to find more such objects in the future. If so, this will allow us to gain further insight into the remnants of stellar mergers and the processes that govern them. “
Read The Misleading 16-Year Space Mystery Revealed a Star Missing Link for more information on this study.
Reference: “Blue Ring Nebula from a Star Fusion Several Thousand Years Ago” by Carrie Hodley, D. Christopher Martin, Brian D. Metzger, Mark Seibert, Andrew McWilliam, Ken J. Shen, James D. Neal, Goodmundur Stephenson, Andrew Monson and Bradley E. Schaefer, November 18, 2020, Nature.
DOI: 10.1038 / s41586-020-2893-5