Nov 19 2020
Earlier in 2004, researchers from NASA’s Galaxy Evolution Explorer detected a huge, faint blob of gas that appeared to have a star at its core. This object was completely different from any other they had seen in the Milky Way Galaxy.
Geometry of the Blue Ring Nebula
The Blue Ring Nebula consists of two expanding cones of debris. The base of one cone is moving toward Earth. Both bases are outlined in magenta, revealing shockwaves created as the debris races through space. Blue represents the material behind the shockwave and is visible only where the cones overlap. Video Credit: NASA/JPL-Caltech/R. Hurt.
Although the blob does not actually produce any light that is perceptible to the human eye, it still appeared blue in the ultraviolet wavelengths utilized by the satellite, and meticulous observations revealed a pair of thick rings inside this object. This made the researchers name it the Blue Ring Nebula.
In the last 16 years, the team has analyzed this object with numerous space- and Earth-based telescopes; however, the more they came learned about this object, the more enigmatic it appeared.
Now, a group of researchers, including Guðmundur Stefánsson, the Henry Norris Russell Postdoctoral Fellow in astrophysical sciences from Princeton University, integrated ground-based observations with comprehensive and theoretical modeling to study the properties of the object.
The article explaining the team’s findings appeared in the Nature journal on November 19th, 2020.
We were in the middle of observing one night, with a new spectrograph that we had recently built, when we received a message from our colleagues about a peculiar object composed of a nebulous gas expanding rapidly away from a central star. How did it form? What are the properties of the central star? We were immediately excited to help solve the mystery!
Guðmundur Stefánsson, Henry Norris Russell Postdoctoral Fellow, Department of Astrophysical Sciences, Princeton University
A majority of the stars in the Milky Way galaxy are in binary systems—that is, two stars circling one another. If these stars get sufficiently close together, such binary systems will meet their end in the form of a stellar merging event—as stars emerge, they tend to expand, and if they are sufficiently close together, one of them can swallow up its orbiting companion, forcing the companion to spiral inward until a collision occurs between the two stars. When the companion star loses its orbital energy, it can emit material away at maximum speeds.
Could that phenomenon shed light on the enigmatic Blue Ring Nebula?
This theory was supported by additional evidence that came from observations made with two varied spectrographs on huge telescopes on the ground—the HIRES optical spectrograph on the 10-m Keck Telescope installed on the summit of Maunakea in Hawaii, as well as the near-infrared Habitable-zone Planet Finder on the 10-m Hobby-Eberly Telescope installed at McDonald Observatory in Texas; Stefánsson contributed in designing, building, and commissioning this new near-infrared spectrograph to identify planets around neighboring stars.
“The spectroscopic observations were key in allowing us to understand the object further, from which we see that the central star is inflated, and we see signatures of accretion likely from a surrounding disk of debris,” added Stefánsson.
Indeed, the spectroscopic data coupled with theoretical modeling shows that the Blue Ring Nebula is consistent with the picture of a merging binary star system, suggesting that the inwards spiraling companion was likely a low-mass star.
Keri Hoadley, Study Lead Author and Postdoctoral Fellow, California Institute of Technology
While scientists have observed the remnants of a few such binary merging events before, all these objects have been obscured by opaque clouds and dust, blocking the view of the characteristics of the central stellar remnant.
The Blue Ring Nebula is the only object to offer an unhindered view of the central stellar remnant, providing a clear window into its characteristics and offering clues about the merging event.
The Blue Ring Nebula is rare. As such, it is really exciting that we were able to find it, and we are excited about the possibility of finding more such objects in the future. If so, that would allow us to gain further insights into the remnants of stellar mergers and the processes that govern them.
Keri Hoadley, Study Lead Author and Postdoctoral Fellow, California Institute of Technology
The article titled, “A blue ring nebula from a stellar merger several thousand years old,” was penned by Keri Hoadley, Christopher Martin, Brian Metzger, Mark Seibert, Andrew McWilliam, Ken Shen, James Neill, Guðmundur Stefánsson, Andrew Monson, and Bradley Schaefer.
The study was funded by Princeton University, California Institute of Technology, the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium.
The study’s authors wish to recognize and acknowledge the highly important cultural role and respect that the summit of Maunakea has always had within the indigenous community in Hawaii. “We are most fortunate to have the opportunity to conduct observations from this mountain,” concluded the authors.
Journal Reference:
Hoadley; K., et al. (2020) A blue ring nebula from a stellar merger several thousand years ago. Nature. doi.org/10.1038/s41586-020-2893-5.
Source: https://www.princeton.edu/